Getting more calcium, either from dietary sources or supplements, reduced women’s risk of death in women during the study period, Canadian researchers found.

In a prospective study, higher total calcium intake was associated with a slightly decreased risk of death that was of borderline significance, but supplementation was significantly associated with reduced mortality risk over a 10-year period (HR 0.78, 95% CI 0.66-0.92), David Goltzman, MD, of Royal Victoria Hospital in Montreal, and colleagues reported online in the Journal of Clinical Endocrinology and Metabolism.

There was no relationship, however, between vitamin D intake and mortality among women.

“Higher amounts of calcium were potentially linked to longer lifespans in women, regardless of the source of the calcium,” Goltzman said in a statement. “That is, the same benefits were seen when the calcium came from dairy foods, nondairy foods, or supplements.”

With regard to supplements, Goltzman noted that the benefit was “seen for women who took doses of up to 1,000 mg per day, regardless of whether the supplement contained vitamin D.”

Calcium and vitamin D are strongly recommended by clinicians for several indications, particularly bone health, but the full risks and benefits of these nutrients are unclear. Some studies have shown that calcium may be cardio-protective, while others have shown an increased heart risk with the mineral, and both high and low serum vitamin D have been associated with increased mortality.

To clarify the association between total calcium and vitamin D intake and mortality, the researchers conducted the longitudinal Canadian Multicenter Osteoporosis Study (CaMos) from 1995 to 2007. They assessed a total of 9,033 patients who had full data on calcium and vitamin D intake.

Overall, 7.3% of men in the study were using calcium supplements alone, 4.4% were using vitamin D supplements alone, and 15.4% were taking both together. For women, 15.2% were using calcium supplements alone, 3.7% were using vitamin D supplements alone, and 29% were using both together.

There were 1,160 deaths over the course of the study.

Overall, there was no clear relationship between calcium intake and mortality for men and women, the researchers reported.

However, they found a possible benefit for higher total calcium intake in women, although it was of borderline significance (HR 0.95, 95% CI 0.89-.01).

Women did, however, have a significantly lower risk of death specifically with use of calcium supplements compared with women who didn’t take them (HR 0.78, 95% CI 0.66-0.92).

There was no dose-response, however, and the association was eventually attenuated as the dosage increased, with lower mortality only for supplement users with a daily dose of less than 1,000 mg.

There were no definitive associations between calcium intake and mortality for men, and overall associations between vitamin D intake and mortality were inconclusive for both men and women.

“Our analysis showed that total calcium intake among women was more likely to be beneficial than harmful, and that the same was true of calcium intake from dairy sources, nondairy sources, and supplements,” they wrote.

Mechanisms for the protective association in women could include the fact that calcium is associated with a better lipid profile and a lower risk of hypertension. Supplemental calcium also protects against potential adverse effects of low calcium intake such as hyperparathyroidism, high serum parathyroid hormone, accelerated bone turnover and bone loss, and cardiovascular effects.

The researchers cautioned that the study was limited by a low response rate, which could result in selection bias. Also, cohort size and mortality rates may have limited the ability to detect significant relationships between calcium or vitamin D intake and death.

Still, they recommended that clinicians “assess dietary intake to meet calcium and vitamin D requirements for bone health and to consider supplementation as necessary to meet the requirements.”