Calcium Demystified: A Consumer’s Guide to the Latest Research

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Calcium Demystified: A Consumer’s Guide to the Latest ResearchDo calcium supplements really cause heart attacks? A recent randomized controlled trial published in the January edition of the British Medical Journal (15 January 2008) concludes that: “Loading with high doses of calcium reduces bone loss but at a cost in heart health that is not justified.”

According to researchers Dr. Ian Reid and his colleagues, the risk of heart attack, stroke and sudden death is about 1.5 times greater for those who supplement with calcium.

How can this be true? Like other nutrients, calcium is interdependent on numerous other factors including the levels of vitamins, other minerals, hormones, the health of the digestive system and the degree of physical activity. To make a simple pronouncement based on one factor, namely calcium supplementation, without looking at the numerous other variables in calcium biochemistry and nutrition, can only lead to erroneous conclusions.

Sure, it’s possible that calcium supplements without a proper diet, enough physical activity, and in the presence of magnesium and vitamin D deficiency leads to heart disease.  But, does this mean that all middle-aged women should stop taking calcium supplements? I think not.


  • Calcium is the most abundant mineral in the body.
  • Calcium is 1.5 – 2% of our body weight.
  • 98% of all calcium is found in our bones, 1% in our teeth and 1% in other tissues.
  • Calcium requires many other minerals for healthy bone formation: magnesium, boron, manganese, zinc, copper, silicon, strontium and phosphorus.
  • Calcium requires vitamins A, C, D and K for optimal metabolism.
  • Calcium absorption becomes less efficient with age.
  • Aside from osteoporosis, calcium deficiency can cause kidney stones and allows the body to accumulate lead.
  • High animal protein (very high in phosphorus) intakes may increase calcium loss through the intestines and kidneys.
  • A very high fat intake also inhibits calcium absorption.
  • Hydrochloric acid helps calcium absorption in the duodenum where most calcium is absorbed.
  • Antacids and prescription acid-suppressing drugs all reduce calcium absorption.
  • Stress can lower calcium absorption.
  • Excess sugar and salt intake leads to calcium loss in the urine.
  • Phytic acid (phytates) found in whole grain foods or foods rich in fiber may reduce the absorption of calcium and other minerals as well.
  • Foods high in oxalic acid (spinach, rhubarb, chard, and chocolate) can interfere with calcium absorption by forming insoluble salts in the gut.
  • 30-80% of all calcium consumed is not absorbed due to all the above factors.
  • Overactive thyroid function can cause calcium loss from bone.


When a person absorbs calcium, regardless of the amount, there is no guarantee that this same calcium will be deposited into the bones. Calcium tends to gravitate towards areas of injury in the body. If the lining of the arteries is damaged, calcium deposits there and causes hardening of the arteries. This could make cardiovascular disease worse. If the kidneys are damaged, the result of calcium deposition could be kidney stones. Calcium also tends to deposit in other soft tissue injured areas like tendons and ligaments causing stiffness or other disability.

Several studies in the past decade have shown that EFAs (Essential Fatty Acids), when combined with calcium, can ensure that calcium deposition will take place in bone and not in the arteries, the kidneys or other soft tissues. EFAs enhance the effects of vitamin D in the gut and improve calcium absorption from the small intestine, reduce the urinary excretion (loss) of calcium, increase calcium that is deposited in the bone, and improve the strength of bone.

The dosage required, for example, for evening primrose to do this in both men and women is between 1500 – 6000 mg. daily. Of course, calcium uptake also depends to variable degrees on the frequency of weight bearing exercises (the more weight bearing exercise you do, the more calcium your body will deposit in the bone), as well as the presence of synergistic minerals such as magnesium, zinc, copper, strontium, silicon, manganese and boron. If your calcium supplement does not contain evening primrose oil, make sure you take an extra 1500 – 6000 mg. of this omega-6 source of essential fatty acids each day to prevent or reverse osteoporosis with much greater assurance.


Calcium toxicity can be a very complex issue and is not simply a question of the dose that one consumes. Virtually any amount of calcium supplementation can be toxic (soft tissue calcification, hardening of the arteries and kidney stones) in the presence of parathyroid disease, or magnesium and vitamin D deficiency. In fact, given the proper conditions, calcium deposits can occur in the arteries or kidneys with daily calcium intakes below the RDA. It all depends on the individual’s nutritional and general health status at the time.

Through the actions of the parathyroid hormones PTH and calcitonin, the body attempts to keep blood levels of calcium within a certain normal range. The adrenal glands, the thyroid, the small intestines, the liver, and kidneys can all modify whether or not calcium absorbs, stays, or comes out of the bones.

Calcium status is also strongly influenced by blood levels of vitamin D, vitamin K, phosphorus, magnesium, boron, strontium, manganese, zinc, silicon and copper. High blood levels of calcium leading to soft tissue calcification will occur with both severe deficiency as well as excessive calcium intake.

Calcium deficiency or very low blood levels of calcium can cause a wide range of symptoms including anxiety, hyperactivity, headaches, irritability, muscle cramps or spasms, numbness and tingling in the hands or feet, palpitations, insomnia, confusion and even depression. Drinking soft water with low or no minerals in it (distilled, reverse osmosis, or calcium deficient water) increases the risk of cardiovascular disease. This is something that has been documented for over 100 years. In other words, a lack of dietary or supplemental calcium causes heart disease.


While North Americans have the highest intake of dairy products in the world, they also have the highest incidence of osteoporosis. Cow’s milk has been linked to numerous digestive disorders including constipation, lactose intolerance, casein (milk protein) allergy, irritable bowel syndrome, colitis, and a long list of allergic and autoimmune disorders including juvenile onset diabetes mellitus. The good news is that there are many healthy calcium alternatives to dairy products. Although cow’s milk has the highest calcium content, many studies demonstrate that absorption is inferior to that seen with calcium from plant sources.

Dark green leafy vegetables have relatively high calcium concentrations. With the exception of spinach (due to its high oxalate content), the calcium from greens is very well absorbed. Kale and other members of the same food family such as broccoli, turnip greens, Brussels sprouts, collard greens and mustard greens are also excellent sources of magnesium, a trace mineral important for calcium utilization (and which is found in only small amounts in cow’s milk). In the past few years, a large number of excellent whole food supplements high in both calcium and magnesium have come out on the market. These include spirulina, chlorella, barley green, green kamut, blue green algae and several others. These all make ideal supplements for children because they are easy to mix with juices, are highly bioavailable, easily absorbed and have a very healthy balance of dozens of trace minerals, antioxidants, vitamins, amino acids and essential fatty acids.

Other natural sources of calcium include cooked beans and peas, seaweeds, soy products like tofu and soy milk, sprouts (e.g. alfalfa), seeds and nuts like sesame, pumpkin and hazelnuts as well as whole grains (e.g. corn tortillas, quinoa).


Whatever the calcium supplement, make sure it is balanced by at least half the amount of magnesium, and that vitamin D levels in your system are adequate. Many health experts recommend a 1:1 ratio of calcium to magnesium in a supplement but this is not something cast in stone (or dolomite, if you prefer).

If a calcium supplement is giving you constipation, just up the dose of the magnesium you take with it to where your bowels are moving well enough to your liking. Ideally, get biochemical tests for the levels of all these nutrients before engaging in any aggressive supplementation.

Since many people are unable to follow a diet with an acceptable calcium intake, or have digestive problems, food allergies that prevent calcium absorption, or a long list of other special situations already enumerated, calcium supplements can become a necessity.

Studies indicate that calcium carbonate, the most widely used calcium supplement, is suitable for most people. While other forms of calcium like calcium citrate, fumarate, gluconate, lactate, malate, orotate, succinate and aspartate may be better absorbed, the disadvantages of using the carbonate forms can be overcome by taking the supplement with food or something that acidifies the duodenal contents (e.g. betaine hydrochloride, apple cider vinegar, or citrus juice).  The big advantage of calcium carbonate is that it is inexpensive and requires fewer capsules or tablets to obtain equivalent amounts of elemental (pure) calcium.

Microcrystalline calcium hydroxyapatite, a hyper-hyped form of calcium supplementation, provides no advantage over calcium carbonate, is more expensive and is the poorest absorbed of all the supplemental forms of calcium.

Coral calcium, another of the over-hyped calcium supplements, has been found to contain traces of lead and other toxic impurities. Like oyster shell calcium, dolomite and bone meal, coral calcium is nothing more than calcium carbonate plus lead and other poisons. None of these are recommended.

Calcium bound to Krebs Cycle intermediates (citrate, lactate, aspartate, gluconate, malate, etc.) have the decided advantage of being better absorbed from the gastrointestinal tract than calcium carbonate, even in the absence of adequate stomach and duodenal acidity. The problem with all of them is the expense and the fact that they are all bulkier molecules requiring more capsules or tablets to achieve the same dosage as calcium carbonate.

Some supplements contain calcium phosphate, which is very poorly absorbed and can block the absorption of iron and other trace minerals. Calcium phosphate is the most constipating of all the calcium supplements and should be avoided.


Every year, without exception, we see counter-intuitive studies concluding nonsense like “calcium supplements cause heart attacks” or “vitamin C causes DNA damage” or “beta carotene causes cancer” or “vitamin E causes heart attacks”. The public panics, throws the vitamin and mineral supplements into the garbage, and heads for the Aspirin and Lipitor bottles.

Examine any of these not so brilliant studies closely enough and you discover that the research was conducted in a test tube as opposed to a human, or that smokers taking prescription cholesterol lowering drugs were used in the study, or that synthetic inactive forms of a vitamin were used. If a study sounds too weird to be true, it’s probably not true.

In the British Medical Journal (15 January 2008) study concluding that calcium supplements increased the risk of heart attack, there was no mention of magnesium or vitamin D blood levels, dietary animal protein intakes, or any of at least a dozen factors influencing calcium metabolism. There is therefore no evidence that calcium supplements taken as part of a balanced nutritional program of diet and vitamin and mineral supplements leads to heart attacks.  If you are still not convinced, see a natural health care professional who can sort out what’s high or low in your body so that the appropriate adjustments can be made to get you into balance.

Calcium Food Sources
Food – Portion – Calcium

Swiss cheese 2 oz. 530 mgs.
Jack cheese 2 oz 420 mgs.
Cheddar cheese 2 oz 400mg
Other cheeses 2 oz 300–400
Yogurt 6 oz. 300 mg
Broccoli, cooked      2 stalks    250mg
Sardines (w/bones) 2 oz 240
Goat milk 6 oz. 240 mg
Cow’s milk 6 oz.  225 mg
Collard greens, cooked    6 6 oounces 225 mg
Turnip greens, cooked 6 oz.    220 mg
Almonds 3 oz.  210 mg
Brazil nuts  3 oz.  160 mg
Soybeans, cooked  6 oz. 150
Molasses, blackstrap 1Tbsp.    130 mg
Corn tortillas (4, w/lime) 2 oz. 125  mg
Carob flour  2 oz. 110 mg
Tofu 3 oz.  110 mg
Dried figs  3 oz.  100 mg
Dried apricots  3 oz. 80mg
Parsley    1 1/2oz. 80 mg
Kelp 1/2 oz. 80 mg
Sunflower seeds 2 oz. 80 mg
Sesame seeds 2 oz. 75 mg

Adequate Intake (AI) for Calcium
Life Stage – Age

Males (mg/day)
Females (mg/day)
Infants     0-6 months
210mg/day (both sexes)
Infants 7-12 months     270 mg/day (both sexes)
Children  1-3 years     500 mg/day (both sexes)
Children 4-8 years
800 mg/day (both sexes)
Children 9-13 years     1,300 mg/day (both sexes)
Adolescents 14-18 years 1,300 mg/day (both sexes)
Adults 19-50 years     1,000 mg/day (both sexes)
Adults 51 years and older 1,200 mg/day (both sexes)
Pregnancy 18 years and younger 1,300 mg/day
Pregnancy     19 years and older – 1,000 mg/day
Breastfeeding 18 years and younger 1,300 mg/day
Breastfeeding 19 years and older 1,000 mg/day

References doi:10.1136/bmj.39440.525752.BE doi:10.1136/bmj.39463.394468.80

Ishitani K, Itakura E, Goto S, Esashi T. Calcium absorption from the ingestion of coral-derived calcium by humans. J Nutr Sci Vitaminol (Tokyo) 1999;45:509-17.

Ross EA, Szabo NJ, Tebbett IR. Lead content of calcium supplements. JAMA 2000;284:1425-9.

Heaney RP, Dowell SD, Bierman J, Hale CA, Bendich A. Absorbability and cost effectiveness in calcium supplementation. J Am Coll Nutr 2001;20:239-46.

Heller HJ, Greer LG, Haynes SD, Poindexter JR, Pak CY. Pharmacokinetic and pharmacodynamic comparison of two calcium supplements in postmenopausal women. J Clin Pharmacol 2000;40:1237-44.

Weaver CM, Heaney RP. Calcium. In: Shils M, Olson JA, Shike M, Ross AC, eds. Modern Nutrition in Health and Disease. 9th ed. Baltimore: Williams & Wilkins; 1999:141-155.

Food and Nutrition Board, Institute of Medicine. Calcium. Dietary Reference Intakes: Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, D.C.: National Academy Press; 1997:71-145.  (National Academy Press)

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