If you are healthy, living at home, and take calcium and vitamin D supplements to prevent broken bones or cancer, you may want to reconsider, according to the U.S. Preventive Services Task Force (USPSTF). The group's new draft recommendations, published online on June 12, add more fervor to the ongoing debate about the benefits and risks associated with these popular supplements.
The USPSTF based its recommendations on a meta-analysis of 136 clinical trials, observational studies and a systematic review evaluating the effects of supplementation on fracture and cancer risk. It concluded that postmenopausal women should not take supplements containing less than 400 international units (IU) of vitamin D and 1,000 milligrams of calcium, noting that there is not enough evidence to evaluate the effects of taking more than those amounts. There was also insufficient data for the task force to determine whether or not healthy younger women and men of any age should take the supplements.
There's no question that "vitamin D and calcium are essential nutrients for a healthy diet," says task force member Kirsten Bibbins-Domingo, an epidemiologist and biostatistician at the University of California, San Francisco. The heart, muscles and nerves cannot work properly without the minerals, and deficiency can also cause bone loss, osteoporosis and tooth damage. Vitamin D is crucial in part because it helps the body to absorb calcium from food. In May the USPSTF recommended that people over 65 take vitamin D supplements if they have an increased risk of falls, for instance because of mobility problems or a history of falling.
But for healthy people the benefits are less clear-cut, Bibbins-Domingo says. Part of the problem is that trials involving vitamin D and calcium are inconsistent—they test different doses for varying lengths of time in diverse populations, which "makes it extra tricky when you try to put them all together and come up with a final analysis," says Erin LeBlanc, an endocrinologist at the Kaiser Permanente Center for Health Research in Portland, Ore. Earlier this week LeBlanc and her colleagues published a study online in the Journal of Women’s Health suggesting that women over 65 with higher blood vitamin D levels gain less weight over time than women with lower amounts.
Despite the difficulty of making firm conclusions about the data, some experts find the USPSTF recommendations, which are open for public comment until July 10, misleading and potentially dangerous. "I think they went too far," says Susan Ott, a bone specialist at the University of Washington School of Medicine. For one thing, "they ignored a lot of people who are getting really no calcium in their ordinary diet."
Indeed, the recommendations only apply to healthy people who are not deficient in either nutrient. (The task force did not evaluate the benefits of supplementation in people with osteoporosis, but the National Osteoporosis Foundation recommends that people with the bone disease consume at least 1,200 milligrams of calcium and 800 to 1,000 IUs of vitamin D daily through food or supplements.) Although the Institute of Medicine maintains that most Americans get enough vitamin D from food and sunlight, the organization notes that nearly 75 percent of American women between the ages of 31 and 50 do not get the recommended 1,000 milligrams of calcium from their food every day, and that a similar percentage of women older than 50 fail to consume their recommended 1,200 milligrams. (To eat 1,000 milligrams without supplementing, a person would have to eat 16 cups of cooked broccoli or drink three and a third glasses of skim milk daily.) "There are a lot of people out there who are only getting half of what we recommend," Ott says, and the USPSTF recommendations do not apply to them.