Regular intake of calcium in too high or too low doses may increase disease risk

According to a new Swedish study women after menopause with long-term inadequate calcium intakes may have a higher risk of death from cardiovascular disease.

The observational study documented cases of death and total calcium intake from diet and supplementation by food frequency questionnaires for 61,443 postmenopausal women for an average of 19 years (1). During the observational period, a total of 17% of the women died: 32% from cardiovascular disease, 16% from heart disease and 8% from stroke. The lowest mean calcium intake was 572 mg/day (the equivalent of five slices of cheese) and the highest 2,137 mg/day. The study results showed that highest rates of all-cause, cardiovascular and heart disease were observed among those participants with a dietary calcium intake higher than 1,400 mg/day. In addition, women with an intake below 600 mg/day showed higher death rates. Women with high dietary calcium intake (above 1,400 mg/day) were more than twice as likely to die com-pared with women who consumed between 600 to 999 mg/day of calcium.

The researchers commented that calcium levels in serum are under tight control, and calcium intake is not normally correlated with calcium serum levels. However, diets very low or very high in calcium can override normal homeostatic control causing changes in blood levels of calcium and factors that may increase risk of cardiovascular events. The serum levels of calcium are strictly regulated and an insufficient calcium intake is met by a more efficient intestinal absorption and renal conservation of calcium. Calcium is also mobilized from the skeleton, which can lead to bone loss and subsequent risk of fractures. In a meta-analysis of 29 randomized controlled trials, calcium supplementation was associated with a 12% reduction in fracture risk and a reduced rate of bone loss in adults 50 years and older (2).To prevent fractures in the elderly by sup-plementation emphasis should be placed on individuals with a low intake of calcium rather than increasing the intake of those already consuming satisfactory amounts. While European health authorities have estab-lished an intake recommendation of 700 mg calcium per day for adults, in the U.S. an intake level of 1,000
to 1,200 mg/day has been defined as adequate.

Earlier this month, results of an US observational study with more than 388,000 participants between the ages of 50 and 71 years indicated that high intake of supplemental calcium may be associated with an increased risk of death linked to cardiovascular disease in men but not in women (3). The researchers concluded that more large studies are needed to further assess the potential cardiovascular health risks of excessive calcium supplement use. Experts commented that the paradigm “the more the better” is not valid for any nutrient intake.

1. Michaëlsson K. et al. Long term calcium intake and rates of all cause and cardiovascular mortality: community based prospective longitudinal cohort study. BMJ. Published online February 2013.
2. Tang B. M. et al. Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis. Lancet. 2007; 370(9588):
   657–666.
3. Xiao Q. et al. Dietary and supplemental calcium intake and cardiovascular disease mortality: The National Institutes of Health–AARP Diet and Health Study. JAMA Intern Med. Published online February 2013.