In April 2021, the US Preventive Services Task Force (USPSTF) published an updated recommendation on screening for vitamin D deficiency in adults. It reaffirmed an “I” statement first made in 2014: evidence is insufficient to balance the benefits and harms of screening.1 This recommendation applies to asymptomatic, community-dwelling, nonpregnant adults without conditions treatable with vitamin D. It’s important to remember that screening refers to testing asymptomatic individuals to detect a condition early before it causes illness. Testing performed to determine whether symptoms are evidence of an underlying condition is not screening but diagnostic testing.
The Task Force statement explains the problems they found with the current level of knowledge about screening for vitamin D deficiency. First, while 25-hydroxyvitamin D [25(OH)D] is considered the best test for vitamin D levels, it is hard to measure accurately and test results vary by the method used and laboratories doing the testing. There also is uncertainty about how best to measure vitamin D status in different racial and ethnic groups, especially those with dark skin pigmentation. In addition, 25(OH)D in the blood is predominantly the bound form, with only 10% to 15% being unbound and bioavailable. Current tests do not determine the amount of bound vs unbound 25(OH)D.1-3
There is no consensus about the optimal blood level of vitamin D or the level that defines deficiency. The Institute of Medicine (now the National Academy of Medicine—NAM) stated that serum 25(OH)D levels ≥ 20 ng/mL are adequate to meet the metabolic needs of 97.5% of people, and that levels of 12 to 20 ng/mL pose a risk of deficiency, with levels < 12 considered to be very low.4 The Endocrine Society defines deficiency as < 20 ng/mL and insufficiency as 21 to 29 ng/mL.5
The rate of testing for vitamin D deficiency in primary care in unknown, but there is evidence that since 2000, it has increased 80 fold at least among those with Medicare.6 Data from the 2011-2014 National Health and Nutrition Examination Survey showed that 5% of the population had 25(OH)D levels < 12 ng/mL and 18% had levels between 12 and 19 ng/mL.7 Some have estimated that as many as half of all adults would be considered vitamin D deficient or insufficient using current less conservative definitions, with higher rates in racial/ethnic minorities.2,8
There are no firm data on the frequency, or benefits, of screening for vitamin D levels in asymptomatic adults (and treating those found to have vitamin D deficiency). The Task Force looked for indirect evidence by examining the effect of treating vitamin D deficiency in a number of conditions and found that for some, there was adequate evidence of no benefit and for others there was inadequate evidence for possible benefits.9 No benefit was found for incidence of fractures, type 2 diabetes, and overall mortality.9 Inadequate evidence was found for incidence of cancer, cardiovascular disease, scores on measures of depression and physical functioning, and urinary tract infections in those with impaired fasting glucose.9
Known risk factors for low vitamin D levels include low vitamin D intake, older age, obesity, low UVB exposure or absorption due to long winter seasons in northern latitudes, sun avoidance, and dark skin pigmentation.1 In addition, certain medical conditions contribute to, or are caused by, low vitamin D levels—eg, osteoporosis, chronic kidney disease, malabsorption syndromes, and medication use (ie, glucocorticoids).1-3
The Task Force recommendation on screening for vitamin D deficiency differs from those of some other organizations. However, none recommend universal population-based screening. The Endocrine Society and the American Association of Clinical Endocrinologists recommend screening but only in those at risk for vitamin D deficiency.5,10 The American Academy of Family Physicians endorses the USPSTF recommendation.11
Continue to: Specific USPSTF topics related to vitamin D