New results from 10 years of follow-up in an observational Canadian study show that calcium intake of up to 1000 mg/day from food or dietary supplements is more likely to be beneficial than harmful. The findings, however, were significant only for women, not for men, report Lisa Langsetmo, MD, from McGill University, Montreal, Quebec, Canada, and colleagues in their paper, published online May 23 in the Journal of Clinical Endocrinology and Metabolism.
"We found in those women who were taking calcium supplements up to 1000 mg per day, as opposed to no supplements, there appeared to be a reduction in mortality. And there was a similar trend in individuals who were getting calcium from dietary sources rather than from supplements," senior author David Goltzman, MD, from McGill University told Medscape Medical News.
The findings are reassuring, said Dr. Goltzman, because some prior research "has suggested that cardiovascular events — heart attacks and strokes — could be increased by calcium supplements." And the new results are consistent with other findings from the Women's Health Initiative, which also found a slight reduction in all-cause mortality with calcium, as did the Iowa Women's Health Study, he noted.
However, the current research did not produce any conclusive evidence about vitamin D, Dr. Goltzman said. "We couldn't say there was any adverse or beneficial effect of vitamin D on all-cause mortality."
Protective Effects of Calcium Seen in Women Only
The researchers studied 9033 community-dwelling men and women participating in the Canadian Multicenter Osteoporosis Study (CaMos) to determine the association between total calcium and vitamin D intake and all-cause mortality among those recruited from 1995 to 1997.
Information on dietary calcium and vitamin D intake was obtained from the abbreviated semi-quantitative food-frequency questionnaire (FFQ) included in the main questionnaire. Foods considered to be excellent sources of calcium included milk to drink, milk products, canned salmon, broccoli, dark leafy greens, dried peas or beans, whole wheat bread, white bread, and tofu. Vitamin D intake was based on milk and yogurt fortified with vitamin D.
Calcium and vitamin D intake from nonfood sources was determined from the inventory of supplements and medications brought to the interview. A questionnaire concerning medication and fracture was mailed annually in all years except those with a scheduled follow-up visit.
There were 1160 deaths during 10-years of follow-up. For women only, there was a possible benefit of higher total calcium intake, with a hazard ratio of 0.95 per 500-mg increase in daily calcium intake and "no evidence of heterogeneity by source," say the researchers.
Use of calcium supplements was also associated with reduced mortality, with a hazard ratio of 0.78 for female users vs nonusers; reductions were significant among those taking doses as high as 1000 mg/day. These associations were not modified by levels of concurrent vitamin D intake, and no definitive associations were found among men.
|Calcium Intake||Hazard Ratio in Men*||Hazard Ratio in Women*|
|Total intake (per 500 mg)||0.99||0.95|
|Dietary: food only, per 500 mg||1.00||0.95|
|Dairy only, per 500 mg||0.98||0.95|
|Nondairy only, per 500 mg||1.23||0.83|
|Supplement nonuser||1.00||1.00 (referent)|
|Low dose (<500 mg)||0.98||0.77|
|Medium dose (500-1000 mg)||1.32||0.75|
|High dose (≥1000 mg)||0.83||0.88|
*Adjusted for confounders: age, study center, education, body mass index, health status, cigarette smoking, alcohol intake, physical activity, sun exposure, self-reported comorbidity (in men and women: hypertension, heart disease, stroke, type 2 diabetes, chronic obstructive pulmonary disease, and kidney stones; in women only: osteoporosis, thyroid disease, irritable bowel disease, and breast and uterine cancer; in men only: prostate cancer), and medication use (aspirin or other nonsteroidal antiinflammatory drugs).
The reason for not finding an effect of calcium intake on mortality in men could be 2-fold, said Dr. Goltzman. "One, we had fewer men (around 3000 out of a total of more than 9000 participants), so there was less power." Also, "we can't exclude biological differences between men and women," he noted.
Calcium From Food Best, but Supplements Fine Too
Dr. Goltzman recommends trying to get calcium initially from dietary sources, noting that a liter of milk contains approximately 800 mg of calcium. "But if that's not possible — because women can't tolerate milk or dairy products, or they have malabsorption problems or just don't like these foods — then supplements up to a 1000 mg per day are fine."
"Most women who are over 50 usually require about a 1000 mg/day; the US IOM [Institute of Medicine] recommends 1000-1200 mg/day depending on age and the woman. Our data would suggest this is reasonable and that 1000 mg per day of calcium is safe and we would recommend people do this for their bone health," he said.
In North America, most calcium is taken together with vitamin D in supplements and that was "the norm" in this study, Dr. Goltzman noted. Nothing in the results suggests that this practice should change, he added.
"The vitamin D has other effects which are beneficial; it facilitates increased uptake of calcium, for example, so we still think it's an important component for bone health."
He said his team also plans to "look at actual circulating levels of 25-hydroxyvitamin D because individuals get vitamin D not only from food sources but from sunlight, so the levels in blood would give an integrated index of vitamin D status, which is a bit more accurate than just looking at intake."
CaMos is currently funded by the Canadian Institutes of Health Research, Amgen, Merck Frosst Canada Ltd, the Dairy Farmers of Canada, Novartis, and Eli Lilly and Co. Dr. Goltzman is an advisory board member or consultant for Amgen, Eli Lilly, Merck Frosst, and Novartis. Dr. Langsetmo has disclosed no relevant financial relationships. Conflicts for remaining authors are listed in manuscript.
J Clin Endocrinol Metab. Published online May 23, 2013. Abstract
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Cite this: Calcium at 1000 mg/d Is Safe, Reduces Deaths, at Least in Women - Medscape - Jun 03, 2013.