USPSTF: Evidence Lacking for Vitamin D Screening

To prevent health problems across the population, what should we do? Answering that question is the job of the U.S. Preventive Services Task Force. It’s been seven years since the USPSTF looked at screening for vitamin D levels. Since vitamin D has been a hot topic in the COVID-19 pandemic, a new update in JAMA on this subject comes as no surprise. But for the vitamin D fan club – a dedicated bunch – this USPSTF report is not very satisfying.

In simple terms, the evidence is inadequate to tell us that screening everyone for vitamin D levels would help or harm public health. Some people might benefit. Some people might be harmed. The decision to test or not depends on individuals and their healthcare providers.

Four Questions

Four simple questions drove this conclusion. The first and most basic goes to the heart of the matter. Has anyone shown that screening for vitamin D levels makes people healthier? The answer is just as simple. No. No one has done an adequate study to answer that question.

Next was the flip side of that question. What could the harm be from screening? Harms are possible, largely from unnecessary treatment that might result. But no evidence exists to show that such harms would actually result.

The third question is more interesting. Does treatment help? The answer is that in many cases, it does not. In the absence of symptoms from low vitamin D levels, taking a supplement has no effect on mortality or the incidence of fractures, falls, depression, diabetes, cardiovascular disease, or cancer. It might help with physical functioning or infections, but the evidence is inconclusive.

Finally, what’s the harm of giving people a supplement when they have no symptoms but low vitamin D levels? The evidence says there’s none – as long as the doses are moderate.

Vitamin D: Necessary but Not Magic

All of this leaves people and their healthcare providers with a pragmatic decision to make. If they have reason to suspect a problem, they can either test their levels or take moderate doses (less than 4,000 units) daily.

Vitamin D is necessary for good health. But its association with a bewildering array of health issues has sown much confusion. People with health issues are often likely to get less sunshine. Thus we have spurious correlations and reverse causation at work. A correlation of depression with lower vitamin D levels, for example, might reflect the people with depression spending less time in active outdoor pursuits, getting less sunlight. The result is lower vitamin D levels.

So while we all need to get enough vitamin D, it’s not the cure for whatever ails us. Getting enough, but not too much, is pretty easy. Screening everyone for low vitamin D levels is unnecessary.

Click here for the USPSTF evidence review and here for the recommendation. For commentaries on this work in JAMA, click here and here. You can find further reporting here, here, and here.

Woman and Screen, painting by Henri Matisse / WikiArt

Subscribe by email to follow the accumulating evidence and observations that shape our view of health, obesity, and policy.

April 14, 2021