Newer Vitamin D Tests Often Inaccurate: Study
Faster, Less Expensive Tests May Overestimate Vitamin D Deficiency
Questions Persist About Vitamin D Testing continued...
Vitamin D, the "sunshine vitamin," plays a well-known and important role in bone health. But in recent years, a raft of research has suggested that low vitamin D may be a factor in a host of other health conditions, including depression, diabetes, cancer, heart disease, and autoimmune diseases.
As a result, doctors have increasingly ordered the test to check vitamin D levels in their patients. The number of vitamin D tests has increased six- to 10-fold over the last decade at some hospitals and laboratories. Industry analysts say the vitamin D tests are now one of the most frequently ordered lab tests in medicine.
"The rate of testing has gone up over the last five to 10 years in an almost exponential fashion," says Naveed Sattar, MD, PhD, a professor of metabolic medicine at the University of Glasgow, in Scotland. Sattar wrote a recent editorial on vitamin D testing for The Lancet, but he was not involved in the research.
Sattar says vitamin D testing has raced ahead of the science, leaving doctors in the dark about how to handle abnormal results.
"Many results are coming back in patients who appear otherwise healthy, but they appear to have low levels. And the physicians don't know what to do, whether they should supplement or not," Sattar says.
Sattar says there's little evidence to suggest that supplementing vitamin D is useful, except perhaps as a treatment for bone loss. The recommended dietary allowances for vitamin D in adults up to 70 years old is 600 International Units (IU) and 800 IU for adults over 70.
While the NIH states a tolerable upper intake level of 4,000 IU, Sattar says that back in the 1950s, when vitamin D was first added to foods, the fortification process wasn't closely monitored and some infants developed dangerously high blood levels of calcium as a result.
Beyond physical harm, however, Sattar says telling someone they are deficient in vitamin D could cause needless anxiety.
"If it were me, I'd be scratching my head. Am I doing something wrong? Should I go spend more time in the sun? Should I be eating certain foods? So that's a hazard by itself," he says.
Someone who looks deficient in D might be prescribed supplements and further testing, increasing costs.
"I think this does need to be looked at carefully," Sattar says.