Postmenopausal women who took calcium and vitamin D supplements demonstrated reduced cancer mortality but increased cardiovascular mortality after a 20-year follow-up period, according to post-hoc analysis results published in Annals of Internal Medicine.
“Commercial dietary supplements are highly variable and not uniformly regulated. Identifying exactly who needs what supplement is predicated in part on dietary intake and habitual diet. All foods contribute a variety of nutrients that can enhance absorption and metabolism in ways that are superior to use of supplements. In the presence of a healthy dietary intake and without other risk factors — including smoking, excess alcohol intake, obesity, etc. — this behavior may far outweigh the nutritional impact that a supplement can provide,” said Linda Van Horn, PhD, RD, Professor Emeritus of Preventive Medicine in the Division of Nutrition and a co-author of the study.
The current analysis evaluated long-term health outcomes of postmenopausal women enrolled in the Women’s Health Initiative (WHI) Calcium and Vitamin D (CaD) trial. The trial included more than 36,000 women ages 50 to 79 years with no history of breast or colorectal cancer from 40 health centers across the United States. Participants in WHI were randomly assigned to receive daily 1000 mg of calcium carbonate with 400 IU of vitamin D3 or a placebo for seven years.
After an average 22.3 year follow-up, participants showed a 7 percent reduction in cancer mortality but, surprisingly, also a 6 percent increase in cardiovascular disease mortality. There was also no statistically significant difference regarding other measures, including overall mortality resulting from all causes.
“These cancer benefit findings appeared to be more beneficial among the women who were not taking a CaD supplement before they were randomized in the study. This is a common theme in nutrition. There are certain recommended dietary allowances based on optimal nutrient intakes (from food), but other than vitamin-D fortified milk and sunlight, the exposure to Vitamin D is limited. Calcium is likewise naturally occurring in milk, yogurt, dairy products and other recommended foods that are often under-consumed by many people,” Van Horn said.
According to Van Horn, while the 6 percent increase in cardiovascular mortality was somewhat surprising, prior studies and meta-analyses have also shown inconsistent results.
“Some [studies] have suggested that increased calcium contributed to what is known as ‘CaC’, or calcification of coronary arteries, but other studies did not so again these findings are inconclusive. It is important to note that in WHI, these results did not appear until 20 years later, so trying to pinpoint the causality without measures of coronary CaC levels (not measured in this cohort) are difficult to pinpoint,” Van Horn said. “Cancer survival is a dominant outcome from this research, but cardiovascular mortality is even more common among an aging population.”
According to Van Horn, WHI data analyses are currently ongoing as many WHI participants enter 80, 90 and 100 years of age.
“These results provide a fascinating opportunity to explore questions like this and other behaviors that are associated with long life and health well beyond the time of the WHI intervention period,” Van Horn said. “It is encouraging to document objectively that among postmenopausal women, healthy lifestyle behaviors practiced long term are beneficial.”
This study was supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health.
