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.
 

To come up with the draft recommendations, the Task Force reviewed three randomized, controlled trials on vitamin D supplements (with or without calcium) to prevent cancer, and 16 trials on vitamin D supplements (with or without calcium) to prevent fractures.

Based on the evidence, the Task Force recommended against daily supplementation with “low doses” (400 IU or less) of vitamin D₃ – a form of vitamin D often used in supplements – and calcium carbonate (1,000 mg or less) supplements for the primary prevention of fractures in postmenopausal women. (Primary prevention means to prevent a condition in people who do not already have it).

The Task Force gave it a D rating, meaning there is “moderate to high certainty” of no benefit and/or actual harm – the potential for kidney stones.

The Task Force also noted that more research is needed to determine whether higher doses of vitamin D and calcium can reduce fractures in postmenopausal women, and whether various preparations of vitamin D (D₂ versus D₃) or different calcium formulations might be helpful.

The Task Force also concluded there is insufficient evidence to assess the effectiveness of:

• vitamin D supplements (with or without calcium) for the primary prevention of cancer in adults
• vitamin D and calcium supplements for the primary prevention of fractures in men or premenopausal women
• more than 400 IU of vitamin D₃ and more than 1,000 mg calcium supplements for the primary prevention of fractures in postmenopausal women.

The recommendations don’t necessarily mean patients should avoid the supplements (and doctors should avoid recommending them), but that everyone should be aware there is not enough evidence to show they are helpful to prevent those cancers or fractures.

But there are other important reasons to take vitamin D and calcium supplements – for example, to help offset a deficiency.

“I want to make clear that our recommendations don’t really apply to treatment of vitamin D deficiency or treatment of [existing] osteoporosis,” notes Dr. Bibbins-Domingo.

Donald Miller, professor and chair of the pharmacy practice department at North Dakota State University in Fargo, echoes that idea. “The U.S. Preventive Services Task Force has a population-wide focus; they are talking about the average person at average risk of cancer and osteoporosis,” he says. “What they are saying is, for the average person they don’t recommend taking vitamin D and supplemental calcium. But that does not mean it is not appropriate for people at higher risk of osteoporosis, [such as] people who have inflammatory arthritis or established osteoporosis.”
 

The Task Force had previously found vitamin D supplements effective in preventing falls in adults 65 years or older, who are at an increased risk for falls. It stands by that recommendation with “high certainty” of a “moderate to substantial” outcome.

“We know that vitamin D is an essential part of a healthy diet – and other groups have been clear that vitamin D at 800 IU is a dose that is essential, and most people can achieve with diet,” says Dr. Bibbins-Domingo. “What we are talking about is supplements, and what we can say is, at 400 IU, it is not helpful. And at higher doses all we can say is there is insufficient evidence.”

“This is like [the soap opera] As The World Turns,” says Mitchell Freedman, DO, physical medicine specialist at the Rothman Institute in Philadelphia, referring to the back-and-forth claims about calcium and vitamin D. “Part of the issue is, nobody knows.”

For example, other recent studies have linked calcium supplementation to a bigger risk – heart attacks.

There’s no question calcium and vitamin D are necessary for healthy bones and good health, but the draft recommendations could just fuel the position that it’s best to get them through a healthy diet.

“I recommend that it is ideal for postmenopausal women to consume 1,200 mg of calcium from calcium-rich food sources. This is the Recommended Dietary Allowance for calcium included in the Institute of Medicine 2011 report,” says Meryl LeBoff, MD, director of the Bone Density Unit at Brigham and Women’s Hospital in Boston and a professor of medicine at Harvard Medical School.

“If a woman’s diet does not include this amount of calcium, I would add a calcium supplement – after calculating her calcium intake from food sources – because it’s important not to take too much calcium from diet and supplements.”

As for vitamin D, Dr. LeBoff says it’s often necessary to supplement – and points to results from the National Health and Nutrition Examination Survey, or NHANES – a large, ongoing, government-sponsored study looking at the health of Americans. “The NHANES data show that about one-third of the population has vitamin D deficiency, and there are many individuals in the population at high risk for vitamin D deficiency,” she says.

In the meantime, if you are unclear about whether you should be taking supplemental vitamin D and/or calcium, ask your doctor. “The Task Force is pretty conservative, because they are recommending things from the population perspective. But it doesn’t preclude anyone from talking with their physician about their personal risks,” says Miller. He notes, for example, that anyone who is taking medications for osteoporosis needs to take make sure they are getting adequate vitamin D and calcium in order to build bones.