Routine vitamin D screening of healthy adults is not supported by current evidence, according to a draft recommendation released Monday by the U.S. Preventive Services Task Force (USPSTF).
The task force, an independent panel of experts that evaluates the latest scientific evidence regarding preventive tests and screening and then makes recommendations based on that evidence, cited several reasons for its decision:
- Experts have not reached a consensus on how to define vitamin D deficiency. Some say that a deficiency occurs when blood concentrations of 25-hydroxy vitamin D fall below 20 nanograms per milliliter (ng/mL), while others say deficiency occurs when the concentrations are below 30 ng/mL.
- The accuracy of the tests used to measure blood concentrations of 25-hydroxy vitamin D is difficult to determine. “The USPSTF found evidence suggesting variation in results between testing methods and between laboratories using the same testing methods,” write the authors of the draft recommendation.
Test results also can be misleading. Studies have shown, for example, that African Americans tend to have lower levels of 25-hydroxy vitamin D than non-Hispanic whites, yet they are at much lower risk of bone fractures, an outcome associated with low vitamin D levels. [As I’ve pointed out here before, although vitamin D is essential for healthy bones, taking vitamin D supplements has not been shown to protect against bone fractures. Nor have they been found to reduce the pain or progression of knee arthritis.]
- No studies have shown that routine screening of people for vitamin D deficiency provides any direct benefits. That’s because, as the task force also points out, there is inadequate evidence to support claims that treating asymptomatic people who have been identified through screening as having a vitamin D deficiency does anything to improve their overall health outcomes.
- On the other hand, no studies have shown that routine screening for vitamin D deficiency harms people, either.
The testing does cause financial harm, however. As one endocrinologist not associated with the task force told MedPage reporter Crystal Phend, “If we do routine screening of the general population, it could cost billions of dollars, not only just for the laboratory testing but also for follow-up testing and the vitamin D treatment itself.”
Indeed, Americans already spend an estimated $600 million on vitamin D supplements each year. (The task force does not, however, consider cost when making its recommendations.)
A marker, not a cause
Despite all this uncertainty, testing rates for vitamin D levels are on the increase. One study found, for example, that the annual rate of primary care visits in which a patient’s vitamin D levels were tested more than tripled between 2008 and 2010.
Research has shown that when asymptomatic and otherwise healthy people are tested, 33 percent to 77 percent will be told they have a vitamin D deficiency, based on the 20 ng/mL and 30 ng/mL threshold numbers. Those people will then believe they need to be treated — usually with vitamin D supplements — even though, as the task force points out, there is no good evidence that treating people without any clinical signs or symptoms of vitamin D deficiency does anything to improve their health or lower their risk of disease.
Some researchers are now beginning to believe that low vitamin D levels may be a marker rather than a cause of deteriorating health. That may explain why low levels of the vitamin are associated with so many diseases — and why giving people supplements appears to do nothing to change the course of those diseases.
The task force is taking public comments on the draft recommendation through July 21. You can read the recommendation and submit your comment through the task force’s website. The final recommendation will be published later this year.