Should I take vitamin D to prevent hip fractures? My physician says my vitamin D level is a bit low.

This week’s post responds to two women asking me the same question. One woman, known to have kidney stones, was prescribed vitamin d alone without calcium as a treatment to lower her chance of having a hip fracture. The woman is healthy with no family history of an increase in fractures. The other woman “succumbed” (her words, not mine) to a test for a vitamin d level. Following the test, her physician prescribed vitamin d and calcium to prevent fractures.

The first woman’s question is easy to answer. The answer is, no, and the treatment of vitamin d alone should not be recommended. The reason for this answer is that there has been nearly 35, 000 women included in at least 11-randomized trials testing vitamin d alone for preventing fractures and these studies show no benefit. A treatment without benefit should be unavailable. In addition, a side-effect of using vitamin d may be kidney stones because it increase absorption of calcium from food; not a good thing for someone with kidney stones.

The second question is more difficult to answer. The table above is from a 2019 review of 6 randomized trials in nearly 50,000 women examining if using vitamin d and calcium can lower the fracture rate. The absolute difference in the proportion having hip fractures over a 3-year time period is small, 0.2%. Most interesting is the lack of information on the harms, or side-effects of taking these agents, but kidney stones, again, are a potential side-effect.

When I searched for information on the use of vitamin d and looked for randomized trials, I found nearly 2000 publications in the last 5 years for vitamin d alone and nearly 550 for vitamin d and calcium. It has always perplexed me why this agent is so hyped and so studied. A recent preventive task force recommendation states that there is insufficient evidence in routine care for any purported benefit of using vitamin d tests or treatments. Despite the lack of information, and small differences in fracture rates found in studies, there has been a nearly 20-fold increase in the use of testing for vitamin d levels and using vitamin d supplements. This is peculiar.

Both women decided against treatment. The first woman was surprised at the lack of benefit. The second woman thought that even if the data on hip fracture is correct, the difference in the probability of fracture is too low to take a medicine routinely.

Again, patients make their best decisions when informed and helped through the decision process. It is hard for me (my opinion) to imagine why the vitamin d test is reimbursed, and hard to imagine why vitamin d is prescribed.