Another Look at Vitamin D

There is still insufficient evidence to determine whether it’s worthwhile to screen for vitamin D deficiency in asymptomatic adults, and the lack of uniformity among testing methods used by laboratories makes interpreting data difficult, according to the U.S. Preventive Services Task Force (USPSTF) in a recommendation statement and systemic review recently published in the Annals of Internal Medicine.

The task force found no studies that looked into the direct benefit of vitamin D screening, and it said there is “adequate evidence that treatment of asymptomatic vitamin D deficiency has no benefit on cancer, type 2 diabetes mellitus, risk for death in community-dwelling adults, and risk for fractures in persons not selected on the basis of being at high risk for fractures.”

There are many testing methods available to measure serum 25-(OH)D levels, but the authors warned that the accuracy of the tests is tough to determine “because of the lack of studies that use an internationally recognized reference standard and the lack of consensus on the laboratory values that define vitamin D deficiency.” Results vary depending on testing method, as well as between laboratories using the same testing methods.

Additionally, USPSTF found that there was “inadequate evidence” on the benefit of treating asymptomatic vitamin D deficiency based on such factors as psychosocial and physical functioning. “Although the evidence is adequate for a few limited outcomes, the overall evidence on the early treatment of asymptomatic, screen-detected vitamin D deficiency in adults to improve overall health outcomes is inadequate,” the guideline stated. Treating vitamin D deficiency in asymptomatic people may reduce mortality risk and falls in institutionalized elderly patients, but not fractures, according to the systemic review.

Despite the task force’s findings, there seems to be a compelling rationale to test for vitamin D deficiency, wrote Robert P. Heaney, MD, and Laura A. G. Armas, MD, of Creighton University in Omaha, Nebraska, in an accompanying editorial. “General assurances that one probably needs extra vitamin D are not as compelling a motivator as knowing one’s number,” they explained. “Thus, whether the practitioner adheres to the widely divergent guidelines of the [Institute of Medicine], the Endocrine Society, or the American Geriatrics Society, measuring vitamin D status seems to be warranted, not so much to diagnose deficiency but to determine patient status relative to the selected guideline.”