Nancy A. Melville
April 13, 2021
Seven years after concluding that evidence was insufficient to recommend screening for vitamin D deficiency in the general population, the United States Preventive Services Task Force (USPSTF) has revisited the issue — and come up with the same conclusion.
Overall, "the current evidence is inadequate to determine whether screening for and treatment of asymptomatic low 25(OH)D levels improve clinical outcomes in community dwelling adults," the Task Force concludes in its statement, recommending an "I" for insufficient.
The statement was published online April 13 in JAMA.
In the absence of screening recommendations, clinicians may be best advised to instead focus on diet and supplementation for those considered at risk, said Anne R. Cappola, MD, of the Perelman School of Medicine at the University of Pennsylvania, Philadelphia.
"Rather than posing the question of screening the general population for vitamin D deficiency, let's focus on ensuring that everyone consumes the age-based recommended daily allowance of vitamin D instead," Cappola, a coauthor of the accompanying editorial, told Medscape Medical News.
No Studies Have Directly Evaluated Benefits of Screening
The latest USPSTF recommendation is based on a systematic review of the benefits and harms of screening and early treatment for vitamin D deficiency in asymptomatic, community-dwelling nonpregnant adults aged 18 or older in the primary care setting with no signs or symptoms of deficiency.
The review found no studies that directly evaluated the benefits of screening for vitamin D deficiency.
However, 26 randomized clinical trials and one nested case-control study evaluated the effectiveness of treatment of vitamin D deficiency with supplementation.
And while observational studies have linked lower vitamin D levels with a multitude of conditions and risks, evidence of any benefit was inconsistent, with none identified for most major outcomes in asymptomatic adults — the focus of the Task Force recommendation.
"Among asymptomatic, community-dwelling populations with low vitamin D levels, the evidence suggests that treatment with vitamin D has no effect on mortality or the incidence of fractures, falls, depression, diabetes, cardiovascular disease, cancer, or adverse events," the review authors stress.
"The evidence is inconclusive about the effect of treatment on physical functioning and infection."
1 in 4 Are Vitamin D Deficient
In terms of the further question of the potential harms of vitamin D screening of asymptomatic individuals, a key concern is the potential for misclassification and over- or under-diagnosis due to inconsistent cut-offs and variability of different screening assays, the review concludes.
However, with the rare exception of vitamin D toxicity from supplementation well above sufficient levels, treatment with vitamin D supplementation appears relatively safe.
With a lack of consensus even over the basic cut-off for vitamin D deficiency, the National Academy of Medicine determined in 2011 that hydroxyvitamin D (25[OH]D) levels below 20 ng/mL are deficient for bone health, with no evidence of different thresholds for any other health condition.
Based on that cut-off, the National Health and Nutrition Examination Survey (NHANES), reported in 2014 that 25% of the US population over the age of 1 was vitamin D deficient, with 18% of the population having 25(OH)D levels of 12 to 19 ng/mL and 5% having very low levels (< 12 ng/mL).
More Work Needed to Determine Groups at Risk
While the Task Force report did not delve into testing or treatment recommendations for symptomatic adults, key established risk factors that may help clinicians identify those who are vitamin D deficient include obesity, receiving little or no UVB light exposure, and older age.
In general, obesity is associated with a 1.3- to 2-fold risk of being vitamin D deficient based on the criteria used, while non-Hispanic Blacks are 2 to 10 times more likely to be deficient compared with non-Hispanic White patients, the Task Force notes.
However, the implications of Vitamin D deficiency in certain populations can vary. For instance, non-Hispanic Black people, despite having a higher prevalence of lower vitamin D levels compared with White people, in fact, have lower reported rates of fractures.
To address the various issues and gain a better understanding of the complexities of vitamin D deficiency, the Task Force calls for further research in key areas.
"More research is needed to determine whether total serum 25(OH)D levels are the best measure of vitamin D deficiency and whether the best measure of vitamin D deficiency varies by subgroups defined by race, ethnicity, or sex," they indicate.
Furthermore, "more research is needed to determine the cut-off that defines vitamin D deficiency and whether that cut-off varies by specific clinical outcome or by subgroups defined by race, ethnicity, or sex."
No Support for Population-Based Screening in Guidelines
With the lack of conclusive evidence, no organizations currently recommend population-based screening for vitamin D deficiency in asymptomatic patients, and the American Society for Clinical Pathology endorses this stance.
The Endocrine Society and the American Association of Clinical Endocrinologists (AACE) meanwhile do recommend screening for vitamin D deficiency in patients considered at risk.
Data show there was as much as an 80-fold increase in Medicare reimbursement volumes for vitamin D testing among clinicians from 2000 to 2010; however, that rate may have leveled off after the National Academy of Medicine reported on set deficiency levels, said Sherri-Ann M. Burnett-Bowie, MD, MPH, Cappola's editorial coauthor.
Burnett-Bowie noted she regularly tests her patients' vitamin D levels, however most of her patients have osteoporosis or fractures.
"I do screen them for vitamin D deficiency since optimizing their vitamin D will improve calcium absorption, which is important for treating their osteoporosis," Burnett-Bowie, of the Endocrine Division, Department of Medicine, Massachusetts General Hospital in Boston, told Medscape Medical News.
In terms of broader testing of asymptomatic patients in the general population, however, any changes in screening will likely be contingent on developments in the effects of treatment, she said.
"Given the challenge in finding benefits of vitamin D supplementation in those who are deficient, it will likely be more challenging to find benefits from wider screening," she concluded.
The USPSTF and editorialists have reported no relevant financial relationships.