June 12, 2012 -- Vitamin D and calcium supplements may not stave off osteoporosis-related bone fractures in most older women, according to new recommendations from the U.S. Preventive Services Task Force.
What's more, there is not enough evidence to say whether supplements of vitamin D, with or without calcium, prevent osteoporotic fractures in men or younger women, or if they can help keep cancer at bay, according to the Task Force.
The panel's one definitive recommendation is that after menopause, women should not take 400 international units (IU) or less of vitamin D and 1,000 milligrams of calcium to prevent bone fractures. There's not enough evidence to show if larger doses of vitamin D might help.
"There isn't evidence to suggest that 400 IU of vitamin D plus 1,000 milligrams calcium can prevent fractures among postmenopausal women who do not live in assisted living or nursing home facilities," says Task Force member Kirsten Bibbins-Domingo, MD. She is an associate professor of medicine at the University of California at San Francisco.
"We know that vitamin D is important, and that a healthy lifestyle should include sources of vitamin D," she says. "It's just not good for preventing fractures at the doses studied," she says.
That is pretty clear cut, but questions remain about what role, if any, vitamin D may have in cancer prevention. "We need more studies to really clarify what it is good at preventing and at how high of a dose," Bibbins-Domingo tells WebMD. "Our bar for prevention is set pretty high."
The same task force recently reported that vitamin D can prevent falls in community-dwelling older adults. The panel based its recommendations on a review of the medical literature.
Vitamin D's Role
Vitamin D deficiency has been linked to host of diseases and conditions such as osteoporosis, heart disease, certain cancers, diabetes, Alzheimer's disease, schizophrenia, and some autoimmune disorders.
These reports led researchers to look into what vitamin D supplements can and can't do, and how much we really need.
Our bodies produce vitamin D when exposed to sunlight. Vitamin D is also added to milk and other foods. But it can be hard to get as much as we need from our diets. As a result, supplements are often needed.
The Institute of Medicine recently raised the recommended daily intake to 600 IU for people aged 1-70 and to 800 IU for adults older than 70. Other groups set the bar even higher.
Vitamin D and Fractures: Is There a Link?
Ethel S. Siris, MD, has mixed feelings about the new recommendations. She is the Madeline C. Stabile Professor of Clinical Medicine and the director of the Toni Stabile Osteoporosis Center at Columbia University Medical Center in New York. "It is good that they are holding back on cancer, but on the bone side, calcium or vitamin D deficiency is not good," she says.
No one is saying that calcium and vitamin D are not enough to prevent fractures. "You need real medicine, but part of the package is to avoid calcium and vitamin D deficiency," she says. "All of the drugs we use require patients to be replete in calcium and vitamin D."
Her advice: Consult your health care provider about what is best for you.
"People who have a real risk for fracture have to go beyond calcium and vitamin D and to medicine, but this doesn't mean they should ignore vitamin D and calcium," she says. "We are not looking for extra; we are looking for enough."
Can Vitamin D Prevent Cancer?
The jury is still out on whether vitamin D can prevent cancer, says Len Lichtenfeld, MD, the American Cancer Society's deputy chief medical officer.
"The studies have been negative, inconclusive, or not well designed to answer the question from a scientific standpoint," he says. "We are left without good medicine to guide people as to whether vitamin D prevents cancer."
"Vitamin D may reduce the incidence of cancer, but the evidence is not sufficient to draw that conclusion," he says. "Many experts do believe that we are relatively deficient in vitamin D as a nation, and people who wish to take supplements should talk to their doctor."