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.”