A government advisory panel today said healthy postmenopausal women should not take daily low doses of vitamin D and calcium to prevent bone fractures. The panel said there is insufficient evidence to evaluate the risks or benefits of larger doses.
In its report, the U.S. Preventive Services Task Force also said existing research is insufficient to assess the risks or benefits of taking vitamin D - with or without calcium - to prevent cancer in adults.
Some studies link higher levels of vitamin D with lower rates of colorectal cancer and reduced risks for other cancer, including breast, prostate and pancreatic cancers. These reports are mixed and therefore inconclusive, according to the advisory panel.
This is the same panel that grabbed headlines recently by recommending against PSA (prostate-specific antigen) tests to screen for prostate cancer in healthy men and advised that women 50 to 74 have a mammogram every other year, instead of annually.
This latest report adds to many conflicting messages about the benefits and risks of vitamin D and calcium supplements.
For years, experts have been touting the health benefits of these nutrients. Both calcium and vitamin D are key nutrients for bone health, and vitamin D also plays a role in muscle health.
The Institute of Medicine, which provides independent advice on health, recommends that people daily get 600-800 IUs (international units) of vitamin D and 700-1,300 milligrams of calcium, depending on age.
Most Americans are meeting their needs for both nutrients, the institute says, partly because many foods have calcium added and many people take vitamin supplements. Many foods, such as milk and yogurt products, are rich in calcium and fortified with vitamin D. Sunlight triggers the production of vitamin D in skin and is a major source of the vitamin for many people.
The task force's draft recommendation looked at doses equal to or less than 400 IU of vitamin D and 1,000 milligrams of calcium for fracture prevention, and recommended against taking them, saying the nutrients slightly increase the risk for kidney stones. The authors add that there is insufficient evidence to draw conclusions about taking larger doses to prevent fractures.
Fractures are a significant health problem, the task force says; every year approximately 1.5 million fractures occur in the U.S. Nearly half of all women older than 50 will have an osteoporosis-related fracture during their lifetime.
"The science is still out for pre-menopausal women and men," with regard to low-dose supplements and fractures, says Timothy Wilt, the lead author on the panel report. "Many people take the supplements, but the science was insufficient to make recommendations for everyone."
Some health experts don't agree with the task force recommendation and say women should weigh options with their physicians based on their own ethnicity and geographic location.
The studies analyzed by the government panel have important limitations, says Jen Sacheck, an assistant professor and researcher in the antioxidants research laboratory at Tufts University in Boston. The research largely involved white people and no accommodation was made for how nutritional needs may vary by where a person lives, she says.
"It's a more complex picture than they're painting," she says. "If you live in New England there are many months of the year when you're not getting adequate amounts of vitamin D from the sun. I check blood levels of young and older people and find them to be low in New England."
Suzanne Steinbaum, director of women and heart disease at Lenox Hill Hospital in New York and an American Heart Association spokeswoman, agrees with the task force that "there seems to be no place for calcium for preventing cancer and fractures.
"To tell people, 'Take calcium and vitamin D to prevent fractures as you get older,' that's not panning out anymore," she says. "Even if you are at risk for a fracture, maybe you have to try other lifestyle changes, like diet and weight-bearing exercise."
Clifford Rosen, a spokesman for the Society of Bone and Mineral Research, notes that the task force discounts a finding from the Women's Health Initiative, a study of 36,282 healthy postmenopausal women, that supplements offer a 10%-11% reduced risk of fractures.
"The government panel's report is a little confusing," Rosen says.
JoAnn Manson, one of the Women's Health Initiative investigators, says in addition to reporting the lower fracture rate, the initiative found "bone density improved among postmenopausal women taking supplements."
Recent research has linked calcium supplements to increased risk of heart attacks, Manson says; she adds that it is best to get calcium from the diet, but some may want to add a low-dose supplement to reach recommended levels.
"The key point about calcium is that more is not better," says Manson, chief of the division of preventive medicine at Brigham and Women's Hospital in Boston.
The National Cancer Institute is funding a 20,000-person study to find whether taking a daily dietary supplement of 2,000 IU of vitamin D or one gram of omega 3 fatty acids reduces the risk of cancer, heart disease and stroke. Manson is directing the study and recruiting men and women for it through this year.
"The science is still out on cancer prevention," says Wilt.
Steinbaum acknowledges that consumers may feel confused and frustrated by changing recommendations. She hopes that people won't give up and feel there's nothing they can do to improve their health. The two old standbys - "eating better and exercising" - still have the greatest impact, she says.