A new study reveals that black Americans display lower levels of vitamin D and greater pain sensitivity than do white Americans. A Vitamin D deficiency may be a risk factor for increased knee osteoarthritic pain in black Americans, the authors conclude. 

Clinical practice guidelines state that vitamin D levels less than 20 ng/mL represent deficiency, and levels between 21 and 29 ng/mL represent insufficiency. Given that low levels of vitamin D are linked to chronic pain and other health conditions, especially in black Americans, the research team set out to investigate if variations in vitamin D levels contribute to racial differences in patients with knee pain caused by osteoarthritis (OA).

Researchers at the University of Florida and the University of Alabama at Birmingham recruited 94 participants—45 black and 49 white patients with symptomatic knee OA—to complete questionnaires regarding their symptoms. The study group was 75% female and an average 56 years old.

In addition, study participants underwent testing that included sensitivity to heat and mechanical pain on the affected knee and the forearm. Researchers measured heat pain threshold as the point when patients indicate the sensation "first becomes painful" and pain tolerance when patients "no longer feel able to tolerate the pain." Mechanical pain measures were determined by the patients' response to pressure in the knee and forearm.

Findings indicate that despite living in a southern sunny climate, 84% of black participants had vitamin D levels less than 30 ng/mL compared with 51% of white subjects. Furthermore, the average vitamin D level for black Americans was 19.9 ng/mL (deficiency), compared with white Americans who averaged 28.2 ng/mL (insufficiency). Black participants reported greater overall knee osteoarthritis pain, and those with lower vitamin D levels displayed greater sensitivity to heat and mechanical pain (experimental pain).

"Our data demonstrate that differences in experimental pain sensitivity between the 2 races are mediated at least in part by variations in vitamin D levels," said lead author Toni Glover, MSN, ARNP. "However, further studies are needed to fully understand the link between low vitamin D levels and racial disparities in pain."