Many people take vitamin D and calcium supplements in the hope of reducing fractures due to osteoporosis and warding off certain cancers. But an independent panel of experts recently concluded there isn’t enough solid proof to support these effects.

The U.S. Preventive Services Task Force, or USPSTF – which is charged with evaluating the risks and benefits of preventive therapies in primary care – issued a draft statement highlighting this lack of evidence.

“We were looking at vitamin D plus or minus calcium for fractures and preventing cancer,” says Task Force member Kirsten Bibbins-Domingo, MD, PhD, an internist and an associate professor at the University of California, San Francisco.

The “one firm conclusion” the Task Force was able to make was that 400 international units, or IU, of vitamin D and 1,000 mg of calcium is not effective in preventing fractures in postmenopausal women, says Dr. Bibbins-Domingo.

However, she adds, there isn’t sufficient evidence to say whether higher doses of either or both supplements would help prevent fractures in postmenopausal women. Additionally, there isn’t enough evidence to say that vitamin D, with or without calcium, can help prevent cancer or fractures in men or premenopausal women, the Task Force found.

“Our goal is to evaluate therapies one would use in generally healthy people without symptoms, and use for a long period of time, to prevent something bad from happening in the future,” says Dr. Bibbins-Domingo. “It may come as a surprise to many people because they are taking these therapies. But what we can say at this point is that the science is not there yet to say that it is effective and that the benefits outweigh the harms.” For example, the USPSTF found a small but potential risk of the formation of kidney stones in those taking 400 IUs of vitamin D and 1,000 mg of calcium.

Past studies have suggested that vitamin D may reduce the risk for cancer. It is critical for helping the body absorb and use calcium, and extra vitamin D and calcium are commonly recommended – especially to postmenopausal women and people on long-term corticosteroid therapy – to maintain strong bones and ward off fractures due to osteoporosis, or bone thinning. Bone thinning is a potential side effect of corticosteroids.