Calcium supplementation questioned
AUCKLAND, NEW ZEALAND. LAF Survey III (June 2001) uncovered a highly significant association between the intake of calcium supplements and episode duration for vagal afibbers – the higher the intake, the longer the episodes. It now appears that calcium supplementation on its own may have other deleterious effects.

Dr. Mark Bolland and colleagues from the University of Auckland, in a recent article published in the British Medical Journal, conclude that calcium supplementation (without concomitant supplementation with vitamin D) is associated with an increased risk of heart attack (myocardial infarction). The NZ study was a meta-analysis of 11 randomized, placebo-controlled trials of calcium supplementation (500 mg/day or more). The average age of the 12,000 study subjects was 72 years, 80% were female, and the average blood level of vitamin D3 (25-hydroxyvitamin D) was about 70 nmol/L or 28 ng/mL, well below the currently accepted "healthy level" of 50 – 70 ng/mL. During the 3- to 4-year follow-up 2.7% of patients in the calcium supplement group suffered a heart attack as compared to 2.2% in the placebo group. There was no significant association between calcium intake and stroke, sudden death or overall mortality.

The authors conclude that calcium supplementation without co-administration of vitamin D is associated with an increased risk of heart attack. They also point out that calcium supplementation by itself has marginal efficacy in the prevention of bone fracture. Finally, they suggest that the higher incidence of heart attacks observed in the calcium-supplement group may have been due to vascular calcification. Other researchers, however, doubt this as it would take longer than 3 to 4 years for arterial calcification to lead to myocardial infarction.

Bolland, MJ, et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events. British Medical Journal, July 29, 2010 [Epub ahead of print]
Cleland, JGF, et al. Calcium supplements in people with osteoporosis. British Medical Journal, July 29, 2010 (editorial) [Epub ahead of print]

Editor's comments: It should not come as a surprise to readers that supplementation with calcium on its own is a bad idea. Ideally calcium should be obtained from dietary sources; however, if supplementation is needed then it should always be accompanied by adequate amounts of vitamin D3 (2000 – 4000 IU/day depending on actual serum level) and vitamin K2 (45 – 100 mcg of menaquinone-7). As far as I know, there is no medical evidence that supplementing with this combination increases the risk of heart attack, stroke or any other cause of death, but there is substantial evidence that supplementation with calcium + vitamin D3 increases bone mineral density and reduces fracture risk. For further reading see osteoporosis

However, calcium + vitamin D supplementation is not the only way to decrease the risk of bone fractures. It is known that bone fractures are relatively uncommon in developing countries where calcium intakes are low and relatively common in developed countries where calcium intakes are high, and many people supplement with calcium in order to ensure an adequate intake. Does this make sense? Dr. Christopher Nordin at the Institute of Medical and Veterinary Science believes it does. Dr. Nordin points out that it is not the total calcium intake which determines bone strength (density), but rather the difference between what is taken in and what is excreted. Research has shown that for each gram of animal protein consumed one milligram of calcium is lost in the urine. This means that a 40-gram reduction in animal protein intake reduces the urinary calcium loss by 40 mg which in turn corresponds to a reduction in calcium requirements of 200 mg (assuming an absorption of 20%). A reduction in sodium (salt) intake of 2.3 grams also reduces urinary calcium loss by 40 mg lowering requirements by another 200 mg. So a person with a low intake of protein and salt might have half the calcium requirements of a person eating a typical North American diet. This and the fact that developing countries generally get more sunshine (vitamin D) than developed countries go a long way towards explaining the difference in the incidence of osteoporosis and bone fractures between different cultures and individuals. Dr. Nordin concludes that there is no single, universal calcium requirement, only a requirement linked to the intake of other nutrients especially animal protein and sodium.[1]
[1] Nordin, B.E. Christopher. Calcium requirement is a sliding scale. American Journal of Clinical Nutrition, Vol. 71, June 2000, pp. 1381-83