Over the last year, there has been considerable debate on the risks & benefits of calcium for women. A new long-term Canadian study of over 6,000 women suggests that calcium intake of up to 1,000 mg per day is not only safe, but it can reduce all-cause mortality by as much as 22%.
The benefit was seen, whether the calcium came from dairy foods, non-dairy foods, or supplements. The findings were published last month in the Journal of Clinical Endocrinology & Metabolism.
In the Canadian Multicentre Osteoporosis Study (CaMos), researchers examined data from 9,033 urban Canadians for 12 years, during which time 1,160 participants died. Participants were 25 years old or older, and randomly selected from a list of residential phone numbers. They were contacted annually. Women and older people were intentionally overrepresented.
Of 6,287 women at baseline, 15% were using calcium supplements alone, 4% were using vitamin D alone, and 29% were using both supplements. Of 2,746 men, 7% used calcium supplements alone, 4% used vitamin D alone, and 15% used both.
Big Bite Out of Mortality
“For women only, we found a possible benefit of higher total calcium intake, with a hazard ratio of 0.95 (95% confidence interval, 0.89-1.01) per 500-mg increase in daily calcium intake,” the authors reported. There was, “no evidence of heterogeneity by (calcium) source; use of calcium supplements was also associated with reduced mortality, with hazard ratio of 0.78 (95% confidence interval, 0.66-0.92) for users vs nonusers with statistically significant reductions remaining among those with doses up to 1,000 mg/d.”
The CaMos project began in 1995, and data collection was completed in 2007.
“Calcium is associated with a reduced risk of fractures, which have been reported to be associated with increased mortality. But these were normal volunteers, fewer than 20% of whom had osteoporosis or fractures,” says Dr. David Goltzman, of the Division of Endocrinology & Metabolism, McGill University Health Centre in Montreal, a co-author of the article.
Dr. Goltzman told Holistic Primary Care that calcium intake has also been associated with a reduction in hyperparathyroidism but he credits the bulk of the mortality reduction to decreases in blood pressure or lipid levels associated with calcium intake.
It is possible, at least theoretically, that calcium intake may lead to decreased in mortality among men as well as women, but the CaMos data showed no such benefit. “We looked at about 3,000 men, compared to close to 6500 women over the ten years period, so the study may not have had the statistical power to show a benefit,” he explained.
The researchers did not examine whether there was a difference in patients who used calcium carbonate, calcium citrate, or calcium phosphate—the three most common fors of calcium used in supplement products. Most consumers in Canada use the former two forms, said Dr. Goltzman.
The CaMos team also examined whether vitamin D intake impacted mortality, but found no effect in subjects who were not also taking calcium. “One of the actions of vitamin D is to facilitate calcium absorption in the gut and intestine, where it acts on the intestinal receptors to improve the ability of calcium to cross into the blood stream,” he explained.
Reconciling Calcium Conflict
CaMos could go a long way in reconciling some of the conflicting viewpoints on calcium that emerged earlier this year when a high-profile study showed that that excess calcium intake may be associated with an increased risk of cardiovascular events. Other studies had found an association between high levels of Vitamin D and an increase in mortality among women.
The CaMos data are contrary to a recent recommendation by the US Preventive Services Task Force against daily supplementation with 1,000 milligrams of calcium or less, based on studies suggesting no net benefit in the primary prevention of fractures among non-institutionalized postmenopausal women
The beneficial effect of calcium observed in CaMos was dependent on characteristics of the participant, such as the person’s overall mortality risk at the outset, and the length of time she had been taking calcium, Dr. Goltzman noted. “If you have a 25-year-old woman taking calcium for a day, she has a very low risk of dying to begin with, so it will have no effect on mortality; whereas if an 80-year-old has been taking it for years, that’s where you’ve seen the highest effect,” he said.
The CaMos findings harmonize with those from the Iowa Women’s Health Study, which also found calcium supplementation lowered risk of mortality in older women. It also aligns well with some of the data from the European Prospective Investigation into Cancer and Nutrition (EPIC), which found a moderate dietary calcium intake (approx.800 mg/day) to be associated with 31% lower risk of myocardial infarction. In addition, the US-based Women’s Health Initiative also found lower risk, Dr. Goltzman added.
Researchers at McGill are presently conducting another study looking at the frequency of hyperparathyroidism in the CaMos study population. “We will probably also be looking at vitamin D levels in blood, to see if they correlate with mortality, as well as issues such as osteoporosis, genetic and other clinical risk factors, and the effects of treatment.”