Taking a second look
In the first, an observational study, nearly 69,000 women, age 50 to 79, answered questionnaires about their health and supplement use and were followed for about seven years. The second study was a clinical trial, in which more than 36,000 women, also age 50 to 79, were given 1,000 mg of calcium in the form of calcium carbonate plus 400 IU of vitamin D per day or placebo for an average of seven years while their health status was monitored. Women who were already taking calcium or vitamin D supplements continue taking them, regardless of their assignment to either the calcium plus D or placebo group.
The original analysis from the clinical trial included all of the women enrolled in the study, but the new analysis only included women who were not already taking calcium or vitamin D when they entered the trial--about 15,000 of the original enrollees. Several new findings were reported:
Hip fracture risk was reduced by 38% in the women assigned to calcium plus D in the clinical trial, compared to placebo.
Hip fracture risk was 35% lower in women taking calcium plus D when the data from the observational study the clinical trial were combined, compared to women who were not taking these supplements.
Compared to no supplements, taking calcium plus D had no impact on risks of heart attack, stroke, or cardiovascular disease in general.
Breast cancer and total cancer risks were lower in women in the calcium plus D group in the clinical trial, but taking calcium and vitamin D showed no cancer protection in the observational study.
Bone benefit without heart harm
The original analysis from the same clinical trial, along with information from other studies, raised concerns that taking calcium with or without vitamin D might increase cardiovascular risk; however, this report found no relationship between calcium with vitamin D and cardiovascular problems. "The strongest evidence for benefit is for hip fracture where calcium and vitamin D supplementation yielded a noteworthy reduction after five years of treatment among women not taking personal supplements," the researchers said, noting that their new analysis showed a greater benefit than the previous analysis.
Taking calcium plus D
Although this report suggests that calcium plus D supplementation is safe, the accumulated evidence, taken together, is still not conclusive. Here are some tips for improving your chance of benefit while reducing your risk of harm:
- For calcium, focus on food. 500 to 600 mg per day is a reasonable amount to supplement. Get the rest of the recommended daily amount from food.
- Get plenty of D. Vitamin D has been linked to cardiovascular protection as well as bone health. According to other research, the greatest benefit to bone may require 800 IU per day or more of vitamin D.
- Take magnesium. Some nutrition experts have suggested that cardiovascular harm might be avoided by balancing calcium intake with magnesium, and many supplements have both. A typical calcium-magnesium supplement has twice as much calcium as magnesium.
(Osteoporos Int 2013;24:567-80)