Should you get your vitamin D level tested?

Jan 21, 2011 2:07 PM

Several million people are expected to undergo lab testing of their vitamin D levels this year, according to a report in this week’s New England Journal of Medicine. But before you roll up your sleeve, ask your doctor why you should get tested and what, if anything, might be done based on the test results, especially if they're only kinda low.

Doctors are finding it “challenging” to interpret results that are only slightly below normal, says the author of the article, Clifford J. Rosen, M.D., from the Maine Medical Center Research Institute in Scarborough and a member of an Institute of Medicine committee that recently released new recommendations for the vitamin. The implications of such results are “incompletely understood,” he says, for many reasons.

For one thing, the accuracy of the test remains problematic, he says, especially in so-called “nonreference” laboratories, such as those that are located in physicians’ offices Moreover, a person’s vitamin D levels can change with the seasons, exposure to sunlight, and, less commonly, with dietary intake. Yet even moderately low results could prompt some doctors to diagnose “vitamin D insufficiency” even if you don’t have obvious symptoms of deficiency such as brittle bones or dental problems. The value of prescribing vitamin D supplement to patients who have moderately low levels is unclear, Dr. Rosen says. And the report last November from the IOM found that while considerable evidence suggests that the vitamin is essential for bone health, it’s less well established whether it has other benefits too, such as protecting against heart disease and cancer.

Bottom Line: Before you get your vitamin D level measured, ask your doctor why you might need to. Also ask what you might have to do if those levels are low. For example, would you need to make dietary changes, or take supplements? Finally, if you do get tested, ask about the lab where the results will be sent, and whether it is reliable.

—Doug Podolsky, senior editor

Read more about good dietary sources of vitamin D.