“No universal vitamin D level” complicates screening for deficiency

19 Apr 2021 --- Screening for vitamin D deficiencies in asymptomatic adults may not impact health outcomes, given variations in optimal D levels and current testing limitations. 

This is according to the US Preventive Services Task Force (USPSTF), an independent body of national experts in primary care and preventive medicine, who reported insufficient evidence to take a stance for or against vitamin D screening.

“Ideal vitamin D levels vary from person to person, and there may not be one single level of vitamin D in the blood that is too low for everyone,” Dr. Michael Silverstein, USPSTF member, tells NutritionInsight. 

“In other words, there is no universal, agreed-upon standard of what constitutes a low level.” 

Multitude of factors
The USPSTF notes that a variety of factors influence vitamin D levels, including sun exposure, obesity and ethnic demographic. 

People who are obese have a 1.3 to 2-fold increased risk of being vitamin D-deficient, depending on the threshold used to define deficiency, says the study. 

Furthermore, the prevalence of vitamin D deficiency is two to ten times higher in non-Hispanic Black individuals than in non-Hispanic white persons, depending on the serum threshold used to define deficiency. 

The Task Force notes that this difference is likely related to differences in skin pigmentation. 

However, how much skin tone is a factor is yet to be determined. 

“The Task Force always considers how our recommendations may help eliminate racial disparities in healthcare, and more research is needed to better understand how vitamin D levels impact people of different racial and ethnic groups,” says Silverstein. 

Factors such as obesity and skin pigmentation may impact vitamin D levels.More research needed
Screening for vitamin D deficiency is done through a blood test, and the most common screening test is to measure the serum 25-hydroxyvitamin D – or 25(OH)D – level in the blood, explains Silverstein.

“However, vitamin D levels in the blood can be difficult to measure accurately.” 

The report notes that different immunoassays can lead to underestimation or overestimation of total 25(OH)D levels.

Test inaccuracy and conflicting recommendations for what constituents deficient 25(OH)D levels, makes reliable screening complicated to implement. 

“While we know that vitamin D is an important nutrient, we need to know more about the levels of vitamin D people need to remain healthy,” notes Silverstein. 

“Once we have enough evidence to better understand that, then research could more clearly determine whether screening for vitamin D helps prevent negative health outcomes.” 

Taking action against deficiency
Although there is not yet enough evidence for the USPSTF to make a recommendation for or against screening for vitamin D deficiency, the Task Force advises that clinicians use their best clinical judgment. 

The organization also asks clinicians to keep an eye out for symptoms or signs of vitamin D deficiency in their patients so they can provide the care needed. Symptoms can include muscle weakness, bone pain and fatigue, he explains. 

 Vitamin D has made headlines for its potential to improve outcomes for COVID-19 patients. The vitamin has also been pegged as an easy and affordable supplement to improve cancer survival rates. 

By Missy Green