A government health panel on Monday chose not to endorse widespread screening for vitamin D levels in healthy adults, despite research suggesting that a majority of Americans may be deficient in the vitamin.
The United States Preventive Services Task Force, an independent group of health experts, decided not to recommend routine testing for vitamin D levels in part because it was not clear whether otherwise healthy adults with low levels would actually benefit from taking supplements of the vitamin. The panel members concluded that there was not enough evidence to either endorse or advise against regular vitamin D screening in most adults, and they suggested that testing is something that should be considered case by case.
"This is not a recommendation for or against it," said Dr. Douglas K. Owens, a panel member and director of the Center for Primary Care and Outcomes Research at Stanford medical school. "In our view, when people have concerns or questions about vitamin D, they should discuss them with their clinicians."
Dr. Owens said that the task force decided to look at the harms and benefits of screening since vitamin D testing is on the rise. Sales of vitamin D supplements have soared in recent years, fueled by a body of research suggesting that the vitamin may help protect against a range of chronic disease. Some studies estimate that more than two-thirds of Americans are deficient in it.
Earlier this year, two large and exhaustive studies in the journal BMJ found that people with low vitamin D levels were more likely to die from cancer, heart disease and to suffer from other illnesses. One of the studies found that middle-aged and older adults who took vitamin D3 — which is found in fish and dairy products and produced in the body in response to sunlight — had reductions in mortality from all causes. But a second study did not find persuasive evidence that vitamin D pills can protect against chronic disease.
There is some debate over whether low levels of the vitamin are a direct cause of disease, or simply an indicator of behaviors that contribute to poor health, like smoking, poor diet and a sedentary lifestyle.
The federal task force issued a draft recommendation based on a review of evidence from more than a dozen studies that evaluated the effects of vitamin D treatment in generally healthy adults. The studies used vitamin D3 doses ranging from 400 to 4,800 international units daily, and they lasted anywhere from two months to seven years.
The panel concluded that the current evidence was "insufficient to determine the net balance of benefits and harms of screening and early treatment of vitamin D deficiency" in generally healthy adults. Dr. Owens said the committee found a number of potential problems with screening.
For one, it is not clear exactly what constitutes a vitamin D deficiency in the first place. Some experts believe that deficiencies should be defined as a blood level of the vitamin that is under 30 nanograms per milliliter. Others say the cutoff should be lower. There are also numerous ways to test for vitamin D, and it is not clear whether some tests are better or more accurate than others.
Another complicating factor is that vitamin D screening can yield unreliable results depending on things like the ethnicity of the person being tested. Studies have found, for example, that the prevalence of low vitamin D is many times greater in African Americans compared to non-Hispanic whites, yet they do not have the higher risk of bone fractures typically associated with low vitamin D. One study last year found that even though African Americans tend to have lower circulating levels of vitamin D, the vitamin is in a more readily accessible form, so their low levels can be misleading.
That suggests that problems may lie with the method of testing, not necessarily the patients. People who are obese may also have paradoxically low levels of circulating vitamin D despite having forms of the vitamin that the body can use.
"Because the accuracy of the test is uncertain, you can misclassify people," Dr. Owens said. "You could tell someone who is not vitamin D deficient that they are. There are those kinds of problems with broader screening."
Dr. Roxanne Sukol, a preventive medicine specialist at Cleveland Clinic's Wellness Institute, said that she often tests her patients for vitamin D, but for varying reasons. In some cases she may have concerns about the quality of a patient's diet. In others, the concern may be that a patient is at risk of low bone density, or that he or she is not getting enough sun exposure to produce sufficient vitamin D.
Dr. Sukol said the draft recommendation would not change her approach to screening, and that she suspects many people may misinterpret the panel's conclusions.
"It doesn't mean you shouldn't test," she said. "They're saying that if doctors decide to do it, that we should tell the patient that we're not positive whether it will make a difference and we're not sure if more good will come from it or more harm."
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