Vitamin D testing: the controversy continues

Sometimes in medicine, the more we know, the less we understand. Awareness about vitamin D deficiency, for example, is high among healthcare professionals and the public, yet there seems to be increasing confusion regarding how, when, and for whom the disorder should be diagnosed and treated.

A study by Wake Forest Baptist Medical Center, recently published in the Southern Medical Journal, showed that the number of diagnoses for vitamin D deficiency tripled in the United States from 2007 to 2010, based on data from the National Ambulatory Medical Care and National Hospital Ambulatory Medical care surveys.¹ This has occurred despite recommendations by the National Endocrine Society (NES) and the Institute of Medicine (IOM) that vitamin D testing be limited to specific patients. IOM believes testing should be restricted to those at risk for weakened bones and fractures,² while NES includes individuals with chronic kidney disease, African Americans, Hispanics, and people who are obese, as well as other groups seen as being at high risk as candidates for testing.³ Confusion results because doctors can be torn between what they read in medical journals about low vitamin D risks and guidelines from prominent organizations like IOM.

The experts disagree…

Many scientific papers have reported that low vitamin D is linked with serious diseases such as rickets and osteoporosis, and some recent studies have linked vitamin D deficiency to elevated risk for some cancers and cardiovascular disease. Yet other publications have concluded that routine vitamin D testing is not beneficial except for those at high-risk for bone diseases and fractures.

Mounting data show that vitamin D deficiencies are on the rise in the United States and around the world. According to the International Osteoporosis Foundation (IOF), vitamin D insufficiency is a worldwide health issue, and the percentage of the world population that has low vitamin D status is high, with some countries exceeding 75%.⁴ It is known that Americans, Canadians, Europeans, and other population groups living in the Northern Hemisphere do not get enough vitamin D from the sun.

“Anyone living north of Atlanta probably has vitamin D deficiency to some degree,” says Lee S. Freedman, MD, an internist practicing in north suburban Chicago. “Vitamin D testing is relatively inexpensive and gives the physician a valuable baseline from which to evaluate success and compliance in using supplements.” Dr. Freedman relies on clinical practicality to guide him on vitamin D testing. “Low vitamin D is so common in the northern United States, especially in the wake of an exceptionally severe winter, that most adults should take supplements daily. Testing not only gives a benchmark to monitor treatment; it provides hard evidence to patients that their Vitamin D levels are low and should be fortified,” he says.

Dr. Freedman likens vitamin D testing to other commonly used and inexpensive diagnostic measures to help prevent strokes and heart disease. “We regularly monitor blood pressure and cholesterol to help prevent serious downstream cardiovascular disorders, and usually recommend simple corrective lifestyle changes, such as better nutrition, losing weight, and exercise. Vitamin D testing serves the same purpose by identifying a deficiency and prescribing safe and inexpensive supplements to increase calcium absorption to help prevent bone weakening and debilitating fractures.”

The controversy continues

Given the high prevalence of low vitamin D and the simple treatment to resolve it, why is routine testing controversial?

It shouldn’t be, according to the IOF and other proponents of universal vitamin D testing. They argue that preventing vitamin D deficiency has a major impact on falls and osteoporotic fractures. Also, vitamin D deficiency is associated with decreased muscle strength in older men and women, and supplementation improves lower limb strength and reduces risk of falling. Vitamin D affects fracture risk through its effect on bone metabolism and risk of falling.

The lead author of the IOF position statement, Bess Dawson-Hughes, PhD, Tufts University, states, “Global vitamin D status shows widespread insufficiency and deficiency. This high prevalence of suboptimal levels raises the possibility that many falls and fractures can be prevented with vitamin D supplementation. This is a relatively easy public health measure that could have significant positive effects on the incidence of osteoporotic fractures.”⁵ 

Despite this recommendation, the Institute of Medicine and the Endocrine Society in their guidelines published in 2011 advocate vitamin D screening only for higher-risk patients, citing that no evidence currently exists to support screening at a population level.

Thus we have very prestigious and influential organizations taking opposite positions on the benefits of routine vitamin D testing. How should this dispute be rectified at the clinical level? 

Clinical perspectives

Laboratories have a role to play in counseling doctors about vitamin D testing. Cindy Johnson, CLS technical supervisor, special chemistry laboratory, University of Minnesota Health, says, “Almost everybody is deficient and should take supplements.” Rather than testing all patients, however, she advises doctors to order vitamin D tests for patients with underlying diseases like osteoporosis for which low vitamin D is problematic. Her lab performs 200 vitamin D tests a day. 

In competing editorials published in 2013 in the journal American Family Physician, the pro-testing argument stresses that even though current scientific evidence does not support universal vitamin D testing, the issue will continue to be debated. Eventually, the extraskeletal benefits of vitamin D may prove scientifically sound in larger randomized clinical trials, resulting in future population-based screening.⁶ 

The opposing editorial emphasizes that scientific evidence on vitamin testing and supplementation is inconclusive at best. Clinicians, therefore, are advised that routine supplementation alone without testing might be a better strategy for treating suspected low vitamin D.⁷ 

What we do know is that insufficient vitamin D is on the rise and poses health risks. It also is well known that vitamin D testing provides valuable information to aid clinical decision making in the primary care setting. For patients with low vitamin D, testing enables their doctors to monitor treatment success and determine if supplements should be increased in dosage or discontinued.

Clearly, the debate on routine vitamin D testing and supplementation will not be resolved without compelling evidence from randomized trials. In the meantime, it may be important to understand which groups of patients are at risk of vitamin D deficiency so that they can get tested or treated as necessary. For many, risk prevention always will be a good clinical strategy.