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.

Read more from WebMD.