information copyright of respective sources and contributors. by Kd. last updated 8.25.05

1. What Calcium Does in the Body
2. Calcium Deficiency
3. How Much Calcium Do You Need
4. Enzymes and Calcium
5. Calcium Content in Foods
6. Calcium Supplements - General
7. Solubility, Absorption and Bioavailability
8. Reading the Label – How much calcium are you getting
9. Relative Calcium Content of Different Forms
10. Should the Supplement Contain Vitamin D
11. Side Effects with Calcium Supplements
12. Which Form of Calcium is Best
13. Sources of Calcium Supplements from Parents
14. Timing – When to give Calcium Supplements
15. Recommendations for Calcium Supplements – Best Bets
16. Calcium Citrate Stops Bone Loss

17. References

1. What Calcium Does in the Body

The majority (99%) of the body’s calcium is found in the skeletal system. However, a very small amount (1%) circulates in the bloodstream where it is vital to internal biochemistry.

The main function of calcium is in the structural development and maintenance of healthy bones and teeth. Calcium in the bone is in two forms, one bound tightly and the other more easily removed. Calcium is removed from the tightly bound part of the bone to maintain blood levels only when dietary intake is inadequate and the more mobile stores are exhausted. Bone undergoes a constant remodeling process with 20 per cent of an adult’s bone calcium re-absorbed and replaced every year.

Calcium is used in many functions: muscle contraction, heartbeat regulation, nerve impulse conduction, neurotransmitters, cardiovascular system, cell division, healthy immune function, the production of saliva, and enzyme activity and for the production and activity of hormones involved in digestion, energy and fat metabolism. It is also involved in the transport of nutrients and other substances across cell membranes. Calcium interacts with sodium, potassium and magnesium to regulate blood pressure and water balance.

A major class of drugs used to lower high blood pressure blocks the channels which transport calcium across muscle cell membranes. Anyone taking calcium-channel blockers should check with their doctor before taking calcium supplements.

When calcium intake is less than optimal the body’s equilibrium mechanisms will pull calcium from the bones to maintain adequate calcium in the blood - thus furthering chances of osteoporosis. Research proves calcium supplements can decrease the risk of bone loss and fractures due to osteoporosis.

2. Calcium Deficiency

Mild calcium deficiency can cause nerve sensitivity, muscle twitching, brittle nails, irritability, palpitations and insomnia. Signs of severe deficiency include abnormal heartbeat, muscle pains and cramps, numbness, stiffness and tingling of the hands and feet, and depression. Children can suffer from rickets, a disease characterized by excessive sweating of the head; slowness in sitting, crawling and walking; insomnia; bone deformities; and growth retardation. In adults, deficiency can lead to osteomalacia with symptoms of bone pain, muscle weakness and delayed healing of fractures.

Those at risk of calcium deficiency include the elderly, people who don’t eat dairy products or other high calcium foods, athletes, those on high protein or high fiber diets, and those who drink a lot of alcohol. High dietary levels of phosphorus cause calcium to be removed from bone and excreted. Phosphorus is found in many common foods such as meat, cheese, processed foods and soda drinks, and people who consume large amount of these foods are at increased risk of calcium deficiency. People on weight-reducing diets are also at risk as they may avoid high calorie foods, which are often good sources of calcium.

Green leafy vegetables such as spinach contain large amounts of calcium but also contain oxalic acid which binds calcium and prevents it from being absorbed. Insoluble fiber, such as that found in wheat bran, reduces calcium absorption; but soluble fiber, such as that found in psyllium and fruit pectins, does not seem to affect absorption.

3. How Much Calcium Do You Need
Although there are some variations between recommendations issued by different groups, the official U.S. and Canadian recommendations for daily intake of elemental calcium are as follows:
Infants 0–6 months = 210 mg
7–12 months = 270 mg
Children 1–3 years = 500 mg
4–8 years = 800 mg
Males and females 9–18 years = 1,300 mg
19–50 years = 1,000 mg
51 years and older = 1,200 mg
Pregnant women 1,000 mg (1,300 mg if under 19 years old)
Nursing women 1,000 mg (1,300 mg if under 19 years old)
Calcium needs to be balanced with magnesium. Most sources say the calcium:magnesium ratio should be 2:1 for most healthy people. Other sources recommend 1:1 for those trying to correct a magnesium deficiency and/or for overall health. Other nutrients are also needed for good calcium uptake, such as vitamin D and K and potassium, but these usually do not need to be supplemented in addition to a regular diet. Sometimes not having enough magnesium will cause calcium to be deficient because there is not enough magnesium for the body to adequately use all the calcium available.

4. Enzymes and Calcium

Gastro intestinal problems interfere with calcium uptake. Certain digestive enzymes have been observed to aid in gut healing which should improve calcium uptake among other nutrients. Taking enzymes with calcium containing foods will facilitate breakdown of the food and improve nutrient release to the body.

Food is the best source of calcium and certain enzymes have been shown to allow intake of more varied foods, including calcium rich dairy, vegetables, and others. This should improve overall “natural” mineral nutritional and calcium availability. Depending on how many foods are returned to the diet, you may not need as much calcium supplements, or even any supplementation at all. Obtaining more calcium through food due to use of enzymes should at least decrease the amount and intensity of any due to the calcium supplement. Gut healing will no doubt improve the effectiveness of any supplements taken.

5. Calcium Content in Foods

Milk (skim), 8 ounces-302 mg Ca
Milk (whole), 8 ounces-291 mg Ca
Low-fat chocolate milk-287 mg Ca
Buttermilk, 8 ounces-285 mg Ca
Breast milk, 8 ounces-79 mg Ca

Nonfat yogurt, 8 ounces-452 mg Ca
Low-fat yogurt, 8 ounces-415 mg Ca
Low-fat yogurt, 8 ounces-314 mg Ca
Frozen yogurt, 1 cup-90 mg Ca

Goat cheese (hard), 1 ounce-254 mg Ca
Part-skim mozzarella, 1 ounce-183 mg Ca
American cheese, 1 ounce –174 mg Ca
Low-fat cottage cheese, 1 cup –155 mg Ca
Feta cheese, 1 ounce-140 mg Ca
Grated Parmesan cheese, tablespoon-69 mg Ca

Sardines with bones, 3 ounces-370 mg Ca
Canned salmon with bones, 3 ounces-180 mg Ca

Collards (frozen, chopped), 1 cup-357 mg Ca
Turnip greens, 1 cup-200 mg Ca
Kale (frozen, chopped), 1 cup-179 mg Ca
Broccoli (cooked), 1 cup-178 mg Ca
Okra (cooked), 1 cup-176 mg Ca
Dandelion greens (chopped, cooked) 1 cup-147 mg Ca
Mustard greens (chopped, cooked), 1 cup-103 mg Ca

Nonfat yogurt, 8 ounces-452
Low-fat yogurt, 8 ounces-415
Low-fat yogurt, 8 ounces-314
Frozen yogurt, 1 cup-90

Goat cheese (hard), 1 ounce-254 mg Ca
Part-skim mozzarella, 1 ounce-183 mg Ca
American cheese, 1 ounce –174 mg Ca
Low-fat cottage cheese, 1 cup –155 mg Ca
Feta cheese, 1 ounce-140 mg Ca
Grated Parmesan cheese, tablespoon-69 mg Ca

Sardines with bones, 3 ounces-370 mg Ca
Canned salmon with bones, 3 ounces-180 mg Ca

Nonfat yogurt, 8 ounces-452 mg Ca
Low-fat yogurt, 8 ounces-415 mg Ca
Low-fat yogurt, 8 ounces-314 mg Ca
Frozen yogurt, 1 cup-90 mg Ca

Vegetable lasagna, 1 piece-450 mg Ca
Calcium-fortified orange juice, 1 cup-300 mg Ca
Cheese pizza, 1 slice –290 mg Ca
Chocolate pudding, 1/2 cup –161 mg Ca
Rice pudding, 1/2 cup-152 mg Ca
Vanilla soft-serve ice cream, 1/2 cup-113 mg Ca
Cheese pizza, 1 slice –290 mg Ca
Chocolate pudding, 1/2 cup –161 mg Ca
Rice pudding, 1/2 cup-152 mg Ca
Vanilla soft-serve ice cream, 1/2 cup-113 mg Ca
Chocolate soft-serve ice cream, 1/2 cup-106 mg Ca
Vanilla ice cream, 1/2 cup-85 mg Ca

6. Calcium Supplements - General

In general, getting nutrition from food is much better than from supplements. A balanced diet is the best way to get calcium because food contains additional nutrients important for absorption and overall health. Studies showing on this are found at:

Supplementing with calcium is often necessary in addition to food intake. There are several issues involved here which complicate the matter. There is no 100% consensus on any part of calcium supplementation and so the consumer needs to be very informed in order to find a product that meets their needs, and educated in knowing how to interpret the mountain of literature available.

- Marketing of Minerals
Selling mineral supplements has become a large, thriving business. This link goes to an article on the marketing of minerals – a nice description of the tactics and considerations involved in selling mineral supplements including calcium. Generally, a company will sell on price, source of calcium form, quality, performance, or service - trying to convince you any of these is the most important thing.

- Scientific, Clinical and Published Studies
In the area of calcium, you can find at least a few studies to support whatever position you want to take. I found a Pubmed journal article saying that with low stomach acid they found no calcium carbonate absorption but good calcium citrate absorption. This was right by another Pubmed journal article saying that with low stomach acid, both carbonate and citrate were absorbed the same. There were studies saying to take calcium with food and without food. Studies saying to take calcium at a different time than magnesium and others saying to take calcium with magnesium. Studies saying it is best taken in the morning and others at night. Studies saying that carbonate is just as absorbable as other forms and dozens saying it wasn’t. So whatever someone’s particular point of view is, they can find a scientific published study – or perhaps a couple dozen - to support that. The information presented here reflects what the majority of the references I found state, and some of the counter arguments as well.

7. Solubility, Absorption and Bioavailability

These are several issues that determine which products will ultimately be beneficial to the body.

- Solubility means the ability of a product to go into solution. The body can only use elemental calcium and so the compound must break up into the individual parts. A product must dissolve first before it can be absorbed.

A supplement should disintegrate in your stomach in an adequate amount of time for it to be useful to your body. To see if your calcium supplement disintegrates easily, place it in a bowl or glass in about 6 oz of vinegar or warm water. Stir occasionally for 30 minutes. It should be completely dissolved. If not, it is likely that this is how it will remain in your body and you should look for a different supplement. Many of the brands containing calcium carbonate in tablet or caplet form will have a note on the bottle saying it dissolved completely within 30 minutes. This test us only appropriate for the actual calcium salt, not multi-vitamins. Most water-soluble forms of calcium dissolve readily in the gut, just make sure it is not in tablet form which could inhibit this reaction. The powdered products usually dissolve quickly, and the liquid supplements already have the compound in solution.

- Absorption means the ability of the elemental calcium in the product to be taken into the body in an acceptable form. Many manufacturers claim their minerals are easily absorbed. There can be two different interpretations of this:

Absorbed into the system - Anything that is one micron or smaller will pass through the stomach wall and go into the blood stream. One could say the product has been "absorbed". Most absorption occurs in the small intestine.
Absorbed into the cells - Just because something passes through the stomach wall into the blood does not necessarily mean it is useable. To be used by the body the minerals must be able to enter individual cells. Micron-sized minerals are too large. The mineral needs to be angstrom size. An angstrom is one million times smaller than a micron. Ionic forms are readily available. Other forms may or may not reach this size.

Factors Improving Calcium Absorption:
1. Small doses – low intake
2. Moderate weight-bearing exercise
3. Lactose
4. Vitamins D and K
5. Adequate, but not excessive, protein
6. Adequate or higher stomach acid - the acid environment of the stomach makes calcium salts more soluble, and therefore easier to absorb
7. Certain nutrients that enhance the absorption and retention of calcium are: potassium, magnesium, zinc, manganese, copper and boron. These nutrients assist in the assimilation of calcium so it can work to help stop bone loss and improve electrolyte balance.

Factors Inhibiting Calcium Absorption:
1. High levels of fat
2. Compounds known as phytates (in dietary fiber) and oxalates (in leafy greens)
3. Low stomach acid
4. Smoking, high refined sugar intake, caffeine, alcohol and excess salt promote calcium excretion
5. High protein diets increase calcium excretion, particularly if the protein comes from meat.

- Bioavailability refers to how well the elemental calcium is used by the body in a desirable way, not just taken into the blood stream and floating around. Even if a particle is small enough to be absorbed into the blood stream, it may not be small enough, or in the right form to be used at the cell level; therefore it cannot meet the body's requirement for calcium. When calcium intake is inadequate to maintain blood levels and other functions, calcium is removed from storage sites in bone. Osteoporosis may develop. It is also possible to have toxicity from too much unusable calcium in the body. At the same time the body may have a calcium deficiency because there is not enough calcium that is in usable form.
Some large mineral forms will simply move through the digestive tract and exit the body. Nothing is gained and nothing is lost except the cost of purchase. At other times the consequences are much more serious. Certain minerals, including calcium, tend to build up in the body and become toxic. When the calcium supplied through dietary intake is too large to go into the cells, some of it gets lodged between cells. That leads to calcium deposits associated with certain types of arthritis. Sometimes it shows up as kidney stones. Other large calcium molecules float around in the blood ready to become plaque inside the arteries. Unusable calcium is also responsible for a number of other disease conditions.

Bioavailability - Metallic Minerals
Some examples of metallic calcium are eggshell, oyster shell, calcium carbonate, dolomite, calcium salts and certain antacids such as Rolaids and Tums. The bioavailability (usability) of metallic minerals is approximately 8-12% in young people. After the age of 35-40 years, usability of the forms of calcium within the human body drops to 3-5%.

Bioavailability - Chelated Minerals
During the chelation process an enzyme, protein or amino acid gets wrapped around a mineral. When a cell is in need of one of those nutrients, the mineral wrapped in that nutrient is taken into the cell. The outer coating gets digested and guess what! There was a mineral hidden in the center! The body was tricked but our goal was achieved; the mineral was taken into the cell. Chelation sometimes increases the bioavailability to 30 or 40%. The usable portion still remains a small percentage of the total intake.

When taking calcium in a usable form, the first thing that happens is the calcium goes for immediate use where it is most needed at the moment. That probably means it will be used by the cells. After the cells have been satisfied, then the extra calcium goes into bone storage. Low bone density starts increasing. When there is not enough calcium to satisfy the cell need, calcium is taken from the bone.

8. Reading the Label – How much calcium are you getting

The FDA says the amount of the element needs to be listed of the label by weight. The form that the calcium comes in is listed in parenthesis beside the weight. So if the label says Calcium 600 mg (as calcium malate), then you know that in each serving you are getting 600 mg of elemental calcium from the compound calcium malate. The weight of the compound form is irrelevant here and maybe much more. You are only interested in the weight of the elemental calcium because that is what your body needs and uses.

If the label does not use this format (then they are in violation of the FDA guidelines for one thing) and just uses the form of calcium and then the weight, such as Calcium Carbonate 1000 mg, then the weight listed is the weight of the entire compound and not the weight of just elemental calcium. In this example, you would need to multiple the weight by the percent of calcium in the compound, so 1000 x 40% = 400 mg of elemental calcium is the elemental calcium you would really be getting.

If one bottle says each serving contains Calcium 250 mg (calcium carbonate),
and another bottle says each serving contains Calcium 250 mg (calcium citrate),
you are getting 250 mg of elemental calcium from either bottle. At this point, look at the form of the calcium and whether it is tablet, capsule, powder or liquid, if this makes a difference to you. The carbonate form, in general, is not very absorbable and some sources put it between 4 and 20%. The citrate form is more absorbable and some sources say from 20-66% more than the carbonate. A chelated or ionic form would also be highly absorbable. See the section on Which Form of Calcium is Best.

Look for supplements that say "purified" or have the USP (U.S. Pharmacopoeia) symbol. The USP symbol, which is voluntary among vitamin and minerals manufacturers, means that the supplement meets certain criteria for quality, strength, and purity.

9. Relative Calcium Content of Different Forms

Calcium Carbonate = 40% calcium
the rest is carbonate. Of that 40% calcium, some sources say only between 4 and 20% of this is usable in the body.
Calcium Citrate = 21% calcium
a chelated mineral, basically calcium wrapped with a covering derived from citric acid. Chelated minerals are generally said to be better absorbed than other forms.
Calcium Lactate = 14% calcium
about 10% of this form is usable. It is the calcium found in dairy products.
Calcium Gluconate = 9.3% calcium
calcium combined with glucose or blood sugar
Calcium Phosphate = 8% calcium and 92% phosphate
Calcium Acetate = 23% calcium

10. Should the Supplement Contain Vitamin D

The calcium supplements on the market come with and without a vitamin D supplement. The reason that vitamin D is often put in calcium supplements is because vitamin D is needed for absorption of calcium from the intestine.

What you need to consider in deciding whether you need a vitamin D supplement with your calcium supplement is if you get enough vitamin D from other sources. Humans can get vitamin D from 2 sources - the action of sunlight on skin, and milk, cereals, and other foods fortified with vitamin D.

Daily exposure of skin (on hands, arms and face) to sunlight as little as 15 minutes per day provides sufficient vitamin D to prevent the bone disease rickets. Vitamin D is also found in milk fortified with vitamin D. In the U.S., 98% of fluid milk is fortified with vitamin D at the level of 100 I.U. per cup. Supplementation with vitamin D is probably not necessary except for people chronically shielded from sunlight and those who do not drink milk daily. However, the amount of the vitamin D supplement in most calcium supplements is at a safe level.

11. Side Effects with Calcium Supplements

Possible side effects of calcium supplements include gas, bloating, constipation, and headache. Excess calcium not used at the cell level can contribute to kidney stones, gallstones, and calcium deposits on joins (arthritis). Taking magnesium will reverse these last problems. Magnesium will dissolve any excess calcium from the body, while helping any needed calcium to assimilate. Citrate does not produce the side effects that carbonate does. Also, taking calcium in smaller doses, less than 500 mg at a time, has been shown to reduce side effects.

12. Which Form of Calcium is Best

There is a fair amount of conflicting information in the area of calcium sources. Most of the studies, literature and references indicated the ionic, chelated or water-soluble forms such as citrate were far more bioavailable and better to use whenever possible (about 85% of sources). Some other studies and sources say that there is no difference in the availability of any form as long as they were pure and refined (about 15%) and even if there is, the carbonate form gives you more for your money. No sources were found that said carbonate was more available than other forms of calcium.

"Although calcium carbonate has the highest concentration of calcium by weight, this form of calcium is relatively insoluble, especially at a neutral pH. In contrast, calcium citrate, although containing about half as much calcium by weight, is a more soluble form of calcium."

Just as with magnesium and most other minerals, most sources all highly recommended an ionic or chelate form such as citrate, malate, fumarate, succinate, or lactate among others. A few studies showed carbonate may be equally absorbable, but not more absorbable. Three sources said under certain conditions of a person being in very good health, no malabsorption, no gastritis or other stomach conditions and having a lot of stomach acid (which is not the norm) then the carbonate may be equally absorbable. Most agreed that carbonate was a benefit over taking nothing, but that other sources were much better. Several of these studies are cited in the reference section.

Completely avoid calcium supplements that are made from bone meal, dolomite, or unrefined oyster shell. These sources may be contaminated with of lead, aluminum, arsenic, mercury, and cadmium.

Every source agreed that calcium carbonate is the lowest cost source of calcium, in general. However, this may be more from the manufacturers point of view than the consumers. I went to 2 health food stores, 3 pharmacies and 1 grocery-drug store doing cost comparisons on brand after brand of calcium supplements (November 2001). I studied at least 20 bottles in each place. I did not find any trend in cost based on the form of calcium. The carbonate containing products were just as expensive or just as cheap as the citrate and other forms. Some brands used just one form calcium and others used a mixture of forms. Costs ranged from $5-10 for a months supply to over $20 for a months supply. In fact, the cheapest source found was a brand of pure calcium citrate. Most online supplement sources also sold calcium citrate, or other water-soluble forms, as inexpensively as calcium carbonate containing products.

More adverse reactions and side effects are seen with the carbonate form calcium (constipation, nausea, irritability, headaches, etc.). Calcium citrate and others are far better tolerated and rarely are side effects noted with these forms.

Most manufacturers use carbonate because it is an older form of calcium, widely available, cheaper for the manufacturer, and reduces bulk. Because carbonate is 40% Ca, products can contain a higher concentration of elemental Ca in the carbonate form (40%). So you may be able to take 2 tablets of calcium to get 600 mg using carbonate, but need to take 4 or more tablets to get 600 mg of Ca using other forms. Several sources noted that although the carbonate is not as available, it may be easier to get someone to take fewer capsules containing carbonate rather than more capsules containing another form that may be less problematic. However, you could also take fewer capsules of the more bioavailable form and still get the same amount of usable calcium.

Because of the large amount of inconsistent information, I decided to divide the sources into groups to see if any trends or consistencies emerged. This is how it played out.

A. Calcium Supplement Vendors
Each commercial company that sold supplements, whether it was carbonate, citrate, ionic, any other form or a blend, adamantly stood by their product as being fully supported by clinical studies, excellent quality ingredients and product, high quality manufacturing practices, and good value for the price.

Those in support of calcium carbonate as a good source referenced these advantages:
1. Cheaper to make (although this was not apparent for the consumer in my observations, see above)
2. Less bulk – this means that someone can take less amount of a product, either fewer pills or less powder, in order to get the same amount of elemental calcium from the source. Whether this elemental calcium becomes available for use by the body is debated.
3. Widely available – most calcium supplements on the market are in carbonate form.
4. Product quality – most manufacturers said THEIR brand of carbonate was very pure in quality and highly available and that the studies showing carbonate was not available used other companies inferior products.
5. Studies – most companies referenced studies supporting their view that carbonate is just as available as other forms and said that contrary studies were old, not conducted fairly, or did not measure absorption properly.
6. People who disagree with this position are not well informed and don’t have accurate information.

Those in support of citrate of other soluble forms as a good source referenced these advantages:
1. Cheaper to use – although the carbonate form was less expensive for the manufacturer, they pointed out the body could not use most of it in that form so the consumer was wasting money on it. So other forms were much cheaper in the long run as a way to get usable calcium in the body
2. More bulk – considered not as relevant because the quantity of a liquid was not that much more to drink, the quantity of a powder was not much more to mix, and most people who swallow pills did not care if they needed to take more. And if your body wasn’t going to use the calcium form anyway, why bother taking it at all.
3. Widely available – although not the most common source, these forms of calcium can be found practically anywhere calcium supplements as sold.
4. Product quality – most manufacturers said THEIR brand of calcium was very pure in quality and highly available and that the contrary studies showing carbonate was just as available used other companies inferior products.
5. Studies – most referenced studies supporting their view that the carbonate form is not as or not very available and said that other contrary studies were old, not conducted fairly, or did not measure absorption properly.
6. People who disagree with their position are not well informed and don’t have accurate information.

Those in support of a blend of calcium forms or who sold more than one form noted these advantages:
1. Blends provide the best of both worlds; a compromise.
2. Selling more than one product covers a larger target market.
3. People who disagree with their position are not well informed and don’t have accurate information.

B. Nutritional Reference Books
I looked up calcium in these reference books available at the health food stores and pharmacies:
- The Natural Pharmacist
- Prescription for Nutritional Healing
- Smart Medicine for Healthy Living
- Dr. Heinerman’s Encyclopedia of Natures Vitamins and Minerals

They contained the following points among other information:
1. If you are going to take a calcium supplement for over a couple of months, you need to balance other minerals with them. Taking a multi-vitamin/mineral supplement is sufficient to do this.
2. Gastritis inhibits the absorption of calcium carbonate.
3. Most, but not all, studies show that calcium citrate is better absorbed.
4. Calcium is better absorbed in small amounts, so taking smaller doses enhances total calcium uptake.
5. When considering supplements, make sure you correctly note how many pills or capsules need to be taken to achieve one serving, or will be needed to get the amount of elemental calcium you want.
6. Calcium carbonate is one of the least expensive forms, but causes constipation and bloating. It is not well absorbed by people with low or reduced stomach acid. Taking with meals improves absorption.
7. Chelated calcium citrate, citrate malate, lactate, gluconate, aspartate, or orotate are water-soluble and well-tolerated forms, although they may be bulkier. These are better for building bone and correcting osteoporosis.
8. Take calcium separately from magnesium and a multi-vitamin/mineral.
9. Citrate is the best form for someone with leaky gut.
10. Soybeans, cocoa, kale, spinach, cashews, almonds contain phytic/oxalic acid which can bind with calcium in the intestines and inhibit absorption.

C. Pharmacists and Nutritionists – talking with actual people
I spoke with several individuals who were not affiliated with any particular company or had no financial interest in the answers. This included 2 well-established and regarded pharmacists, 3 nutritionists, and 2 people who worked in health food stores and seemed to know a lot about the subject (one of these admitted she really didn’t know much about it and so her answers are not included).

I asked first, “I am looking for a good calcium supplement. Which form would be best?”
Every person answered, “Calcium citrate.”
Then I asked, “What about calcium carbonate?”
Every person answered, “No, that is one of the least absorbable forms. The other more soluble forms are better.”
Then I said, “It is for a child with gut problems….leaky gut, some malabsorption.”
Every person answered, “Oh, then you definitely want the more soluble citrate form.”
Then I asked, ”What if the carbonate was ground up really, really fine…would that make it more absorbable?”
Every person answered that yes, that would help, but they still felt the citrate or a liquid of an ionic form would be best, unless a sweet tasting carbonate form was the only way to get someone to take it (such as the newer chocolate chews or the fruity Tums). They felt the carbonate was “okay” but not the best and to consider other forms. Carbonate would be “okay” if someone was in good health to begin with, but not the best if one had gut problems or was trying to treat a deficiency or osteoporosis. One pharmacist said if the carbonate was very fine and contained an acidifying agent, that would be good. All felt the liquid ionic, or water-soluble products were good and facilitated absorption.

Although some sources of calcium are absorbed better than others, inadequate information exists to compare them all and determine if one is always best. Calcium carbonate is a good source of calcium as long as adequate stomach acid or acid foods are present. Most people absorb calcium better from calcium citrate than from carbonate because it is soluble in water. The citrate form is also considered safer from side effects and better tolerated.

13. Sources of Calcium Supplements from Parents

Comments from parents of the enzymesandautism and other message boards on calcium supplements they have found beneficial.

1. “We use calcium fortified beverages such as orange juice, cereals and other foods.”

2. “Brainchild Nutritionals has a liquid calcium/magnesium supplement that is tasty. It has a coconut flavor. It's in the "kreb's cycle" form...supposedly the best absorbed.”

3. “Nutrition Now's Calci Yums. They have no artificial colors and are just like pieces of salt water taffy --yummy!!!! At health food stores, or online at”

4. “Nature's Plus Children's Chewable Calcium Animal Parade. This is in Vanilla Sundae Flavor, taste very good and my kids like it very much. It is GFCF and available at health food stores. The form is a very absorbable aminoate.”

5. “Calcium ascorbate is buffered vitamin C, or called ester-C. Since vitamin C helps the stomach to heal and strengthen the immune system, this is another good source. The buffered form is non-acidic and tasteless (although one brand I bought was a little tart). I use tablets that have 500 mg C and about 50 mg Ca each, plus bioflavonoids for easier absorption. Also, I use the powdered crystals that I measure out. One fourth teaspoon is 1066 mg C and 117 mg Ca. I buy a local brand, and have used Thompson's brand too.”

6. “Kirkman Labs calcium powder. You can bake with it, but my son, who generally doesn't like sweet stuff, will lick his finger and dip it into the powder and take the required dose, no problem.”

7. “Viactiv calcium chews and other similar products. Tasty flavors, does contain some casein. The big advantage is it is like getting a piece of healthy candy so people are more motivated to take it. “

8. “We use CalMax from Dr. Michael Pinkas. It is kind of expensive since you have to order at least 4 bottles at once but it is awesome. It is a calcium/magnesium drink that dissolves in hot water like an alka-seltzer. The number is 1-800-280-5590 to order. It has a slight lemon taste. My son takes it with no problem but I put ice in it to make it cold.”

9. “I've heard liquid is the best for all minerals. We use liquid magnesium/calcium by Swiss Flora."

10. “Rhino Calcium from Miss Robens or the health food store. If your child likes chewable vitamins and doesn't mind chalky calcium ones, this one has the magnesium. It is GFCF with no preservatives or colorings.”

11. “We use the Twinlabs CalQuick liquid. We used to not refrigerate it, like it says, but now do, and it goes down much better, and smells and tastes better through the whole bottle. Other liquid calcium supplements are available at health food stores as well. Trace Minerals makes a line called Liquimins.”

12. “We get our calcium in a distilled water base from the Apothecary in Maryland. They made it that way for us, once I specified GFCF. The Apothecary can be reached at 1-800-869-9159. This is the main tel. number. Then, there is a direct number to the compounding section of the pharmacy: 1-800-869-9160. Here you can speak directly to a pharmacist who will make up your prescription. I found Ron to be very helpful. We discussed various ways to prepare a GFCF liquid calcium without dyes or flavorings. They can make up anything else you might want. The one thing to remember is that you will need to fax them a doctor's request before they will compound. We simply asked our doctor to fax us a prescription for liquid calcium (we just bought a home fax, so that communication between our various doctors is proving much easier). Also, custom compounding is not cheap. A 30 days supply of the liquid calcium is $13.95, not including shipping. Also, do get the Apothecary to send you their brochure--they have a lot of good stuff in there, like colostrum, melatonin, vitamins and nutrients. They also have a useful website:”

13. “Go to a health store and look for a children’s calcium supplement. They have all kinds. My daughter takes Nature's Plus Vanilla Sundae Flavored Animal Parade and our son takes a liquid that is mint flavored. If you can't find anything right away give her plain Tums. I called on these a while back and they are made out of oyster shells. Be careful on calcium supplement juices as they are usually fortified with a milk by-product like lactate or lactic acid which could be a problem if your daughter is really sensitive.”

14. Timing – When to give Calcium Supplements

When to give calcium supplements depends on the type of calcium and what other supplements you may be giving. Calcium carbonate needs to be taken with food because it needs more acidic conditions to be absorbed. Carbonate needs acidic conditions to appropriately dissociate the calcium to be absorbed by the body. Eating induces the stomach to produce digestive acids. Calcium citrate and most all of the other forms that are chelated, ionic, or water soluble do not have this requirement and can be given anytime in the day, with or without food.

There is a lot of conflicting opinion on giving calcium and magnesium together or separately. A lot of the supplements sold contain calcium and magnesium together. However, a lot of the references say to give them separately because minerals tend to compete with one another for absorption sites. A few sources say if you give calcium and magnesium together along with zinc, the minerals will “self sort” because they will be competing for the transport sites at the same time. This theory would suggest that to get as much of each nutrient absorbed, giving them separately allows the most absorption of each mineral.

Smaller doses given throughout the day are better than one large dose. Most of the references supported studies showing that more calcium was absorbed through smaller doses. Smaller doses also lessen the possibility of side effects. Giving calcium during the day enhances absorption into the bones. Giving calcium at bedtime may enhance relaxation and sleep.

I had a few chats with some pharmacists over this. They both said that Tums has calcium carbonate but the antacid properties of the Tums makes the calcium in it not as soluble, so it is not as good a source for calcium as it is made out to be. Another pharmacist pointed out that for years people with an ulcer or acid stomach would be told to drink milk to counter it. However, this didn't work out as well because at first the milk would make the stomach feel better by making it more alkaline, but the drinking of milk would induce stomach acids, and thereby cancel out the effect. Now drinking milk isn't recommended for people with ulcers.

Here is something else. Don't bother trying to get your kid to eat 5 cups of spinach or kale per day to get their calcium. These two foods also contain oxalic acid which inhibits the absorption of the calcium from the food. Soy also contains phytic/oxalic acid which binds with calcium in the gut thus making it unavailable for absorption. So soy milk fortified with calcium isn't quite as good as just drinking milk, or getting it in some other way. So take your soy foods at a different time than your calcium supplements.

15. Recommendations for Calcium Supplements – Best Bets

  • Buy a supplement in a capsule, liquid or powdered form instead of a harder tablet or caplet that are often harder to dissolve and release the elemental calcium.
  • Know how much elemental calcium is in the supplement. This will be listed on the label as Calcium XXX mg (as the form in parenthesis).
  • Do not use bonemeal, oyster shell or dolomite as a source of calcium. The Food and Drug Administration has issued warnings that bonemeal and dolomite could be dangerous because these products may contain lead, aluminum or other undesirable elements.
  • Get a very soluble, highly absorbable form. Chelated and ionic forms are good, safe bets.
  • Since the body cannot absorb more than 500 mg of calcium at a time, it is better to give smaller doses of calcium (500 mg or less) throughout the day rather than one large dose.
  • Vitamins D and K help keep calcium in the bones. Most people do not need to supplement with extra vitamin D if they have adequate sunlight and eat other foods or milk with vitamin D.

16. Calcium Citrate Protects Against Bone Loss

Calcium Citrate Shown to Have Superior Bioavailability and Protects Against Bone Loss
November 21, 2000 Journal of Clinical Pharmacology/MedscapeWire

An important follow-up study that reaffirms calcium citrate's superior bioavailability when compared with calcium carbonate also provides new evidence of calcium citrate's role in protecting against bone loss.

The study, published in the November issue of the Journal of Clinical Pharmacology, used 3 measures to determine calcium bioavailability — serum calcium, urinary calcium, and serum parathyroid hormone (PTH). This randomized crossover study compared the single-dose bioavailability and effects on PTH of commercial calcium citrate 250 mg (Citracal, Mission Pharmacal) and calcium carbonate 500 mg (Os-Cal, SmithKline Beecham) supplements in postmenopausal women.

"The initial study we conducted in 1999 showed that calcium citrate is more readily available to the body than calcium carbonate," explained study author Howard J. Heller, MD, assistant professor at the Center for Mineral Metabolism and Clinical Research at the University of Texas Southwestern Medical Center in Dallas. "We expanded the trial and our measurement methods to determine if one form of these commercially available calcium supplements was a better choice in postmenopausal women. We found that the tablet formulation of calcium citrate in the form of Citracal was more bioavailable than calcium carbonate, even when given with a meal. Several studies have established that calcium citrate is more bioavailable than calcium carbonate when the subject is fasting; however, some authors have previously suggested that the two forms of calcium are equally bioavailable when given with a meal.

"Moreover," Dr. Heller continued, "calcium citrate produced greater suppression of serum PTH by more than 50% over calcium carbonate. This provides physiological evidence that calcium citrate was better absorbed. We additionally found that calcium citrate may be particularly advantageous in those who absorb calcium poorly from calcium carbonate."

Parathyroid suppression is critical in maintaining bone because PTH is responsible for age-related bone loss. When the body senses a deficit in calcium, it responds to the challenge by increasing PTH levels and leaching calcium from the bones.

In another study from Mayo clinic, researchers found that calcium citrate supplementation effectively lowered serum PTH values to those found in premenopausal women, ultimately protecting them against bone loss.

Dr. Heller and his colleagues compared the calcium absorption of calcium citrate 350 mg (Citracal) and calcium carbonate 500 mg (Os-Cal) after a single oral load (500 mg calcium), taken with a meal, by calculating the peak and cumulative change in serum calcium from baseline, offering a direct measure of calcium bioavailability. Similarly, the curve of decline in serum PTH from baseline over time was used to assess the ability of calcium supplements to suppress parathyroid function. To adjust for daily biological variation and the effect of the meal alone, the value from the placebo phase was subtracted from the corresponding value for calcium citrate and calcium carbonate, allowing their actions to be compared independent of these variables.

This study was conducted as a follow-up to a previous study by Dr. Heller, published in the November 1999 issue of the Journal of Clinical Pharmacology, which was the first direct comparison of commercially available calcium supplements. In that study, it was proven that the calcium supplement formulation calcium citrate was 2.5 times more bioavailable than calcium carbonate, even when given with a meal, the optimum method of ensuring calcium carbonate absorption. J Clin Pharmacol. 2000;40:1237-1244

17. References

Many references can be found on the internet or in Pubmed by searching for calcium, calcium supplements, and calcium absorption. Just a few are given below.

1. General article on calcium

2. Citracal - A lot of calcium information here.

3. Kansas State Research and Extension

4. General information on calcium supplements

5. The Natural Pharmacist – online nutrition reference

6. General information

7. Excerpt from lecture by Dr. Steven Whiting, Director, Institute of Nutritional Science Reproduced with permission.
8. Table comparing calcium citrate and carbonate, and vitamin D
9. Functional Foods

10. Forms and availability

11. Calcium Availability from Food

Selection of References from published journal articles/studies:
12. Calcium bioavailability from calcium carbonate and calcium citrate.
Fourteen normal subjects took 1000 mg calcium orally as calcium citrate or calcium carbonate. The amount of calcium absorbed was estimated from the rise in urinary calcium. The urinary calcium following calcium citrate load significantly higher (by 20-66%), whether expressed as the total amount or as the increment above basal (fasting) excretion. Thus, calcium citrate provides a more optimum calcium bioavailability than calcium carbonate.

J Clin Endocrinol Metab 1985 Aug;61(2):391-3 Related Articles, Books
Nicar MJ, Pak CY. PMID: 4008614 [PubMed - indexed for MEDLINE]

13. Pharmacokinetics of calcium absorption from two commercial calcium supplements.
Heller HJ, Stewart A, Haynes S, Pak CY.

In conclusion, Citracal is much more bioavailable than Os-Cal.

J Clin Pharmacol 1999 Nov;39(11):1151-4 Related Articles, Books, LinkOut
Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas 75235-8885, USA.
Publication Types:Clinical Trial Controlled Clinical Trial
PMID: 10579145 [PubMed - indexed for MEDLINE]

14. Dose dependency of calcium absorption: a comparison of calcium carbonate and calcium citrate. Harvey JA, Zobitz MM, Pak CY.

These results confirm the superior calcium bioavailability from calcium citrate as compared with calcium carbonate.

J Bone Miner Res 1988 Jun;3(3):253-8 Related Articles, Books
Center in Mineral Metabolism and Clinical Research SWMS UTHSCD, Dallas.
PMID: 3213620 [PubMed - indexed for MEDLINE]

15. Pharmacokinetic and pharmacodynamic comparison of two calcium supplements in postmenopausal women. Heller HJ, Greer LG, Haynes SD, Poindexter JR, Pak CY.

Compared with calcium carbonate, calcium citrate provided a 46% greater peak-basal variation and 94% higher change in area under the curve for serum calcium and a 41% greater increment in urinary calcium. Moreover, the decrement in serum parathyroid hormone concentration from baseline was greater after calcium citrate. In conclusion, calcium citrate is more bioavailable than calcium carbonate when given with a meal.

Center for Mineral Metabolism and Clinical Research, University of Texas Southwestern Medical Center, Dallas 75390-8885, USA.
J Clin Pharmacol 2000 Nov;40(11):1237-44 Related Articles, Books
Erratum in: J Clin Pharmacol 2001 Jan;41(1):116
Publication Types: Clinical Trial Randomized Controlled Trial
PMID: 11075309 [PubMed - indexed for MEDLINE]

16. Absorbability and cost effectiveness in calcium supplementation.
Heaney RP, Dowell SD, Bierman J, Hale CA, Bendich A.

BACKGROUND: Cost-effectiveness of calcium supplementation depends not only on the cost of the product but on the efficiency of its absorption. Published cost-benefit analyses assume equal bioavailability for all calcium sources. Some published studies have suggested that there are differences in both the bioavailability and cost of the major calcium supplements. RESULTS: All three calcium sources (marketed calcium carbonate, encapsulated calcium carbonate and marketed calcium citrate) produced identical 24-hour time courses for the increment in total serum calcium. Thus, these were equally absorbed and had equivalent bioavailability. Urine calcium rose slightly more with the citrate than with the carbonate preparations. but the difference was not significant. Serum iPTH showed the expected depression accompanying the rise in serum calcium, and there were no significant differences between products. CONCLUSION: Given the equivalent bioavailability of the two marketed products, the cost benefit analysis favors the less expensive carbonate product.

J Am Coll Nutr 2001 Jun;20(3):239-46 Related Articles, Books
Creighton University, Osteoporosis Research Center, Omaha, Nebraska 68131, USA.
PMID: 11444420 [PubMed - in process]

17. Bo-Linn, G.W. et al., "An Evaluation of the Importance of Gastric Acid Secretion in the Absorption of Dietary Calcium," Journal of Clinical Investigation, 73:640-647, 1984.
Study measuring gastrointestinal absorption of calcium following a single meal. A large dose of the H2 antagonist cimetidine, which significantly reduces stomach acid, had no effect on calcium absorption in both normal subjects and in one patient with diagnosed achlorhydria (absence of stomach acid).

18. Relation between gastric secretion of acid and urinary excretion of calcium after oral supplements of calcium. Hunt JN, Johnson C.

The object of this study was to determine in 12 healthy subjects the relation between gastric secretion of acid and absorption of calcium from two different preparations of calcium, as judged from increased outputs of calcium in the urine. The increase in urinary output of calcium after solid calcium carbonate was greater in the subjects with the most gastric secretion of acid. The absorption of calcium after a solution of monocalcium citrate was independent of gastric secretion of acid. In the four subjects with the least gastric secretion of acid, there was no absorption of calcium after calcium carbonate, but the absorption after monocalcium citrate was as great as that for those who secreted greater amounts of acid.

Dig Dis Sci 1983 May;28(5):417-21 Related Articles, Books
PMID: 6839905 [PubMed - indexed for MEDLINE]

19. A study in the New England Journal of Medicine by Dr. Robert Recker has shown that calcium absorption from calcium carbonate was lower in patients with achlorhydria (low or no stomach acid) than in normal subjects. Yet when calcium carbonate was taken with a meal, calcium absorption was normal even in patients with no stomach acid.
Recker, R.R., "Calcium Absorption and Achlorhydria," New England Journal of Medicine, 313:70-73, 1985.

20. Stomach acid IS NOT necessary for carbonate absorption
Levenson, DI and R.S. Bockman, "A Review of Calcium Preparations," Nutrition Reviews, 50: 221-232, 1994.
Those studies that measure actual systemic calcium absorption show that calcium from most sources is well absorbed in healthy individuals. They also show that little acidity is necessary for calcium absorption, and that no basal gastric acidity seems to be necessary if calcium is taken with meals.

21. Stomach acid IS necessary for carbonate absorption (and other general information)
NIH Concensus Panel

22. Sheikh, M.S., et al., "Gastrointestinal Absorption of Calcium from Milk and Calcium Salts," New England Journal of Medicine, 317:532-536,1987.
This study found no difference in the amount of calcium absorbed from equivalent amounts of various sources, including milk and several calcium salts, in fasting, healthy, young volunteers. This was true regardless of the solubility of the various forms of calcium.

23. Meta-analysis of calcium bioavailability: a comparison of calcium citrate with calcium carbonate.

Sakhaee K, Bhuket T, Adams-Huet B, Rao DS.

RESULTS: Calcium absorption from calcium citrate was consistently significantly higher than that from calcium carbonate by 20.0% in the whole set, by 24.0% in Category A, by 27.2% on an empty stomach, and by 21.6% with meals. CONCLUSION: Calcium citrate is better absorbed than calcium carbonate by approximately 22% to 27%, either on an empty stomach or co-administered with meals.

Am J Ther 1999 Nov;6(6):313-21 Related Articles, Books
University of Texas Southwestern Medical School, Center for Mineral Metabolism and Clinical Research, Dallas, TX 75235-8891, USA.
Publication Types: Meta-Analysis PMID: 11329115 [PubMed - indexed for MEDLINE]



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