Vitamin D deficiency may contribute to pain in osteoarthritis

Black Americans with knee osteoarthritis have higher rates of vitamin D deficiency and pain sensitivity when compared to white Americans, says a new US study.

In the study, 45 black and 49 white patients (average age of 56 years) with knee osteoarthritis completed questionnaires regarding their symptoms and underwent sensory testing, measuring sensitivity to heat and pain on the affected knee and forearm (1). In addition, the participants’ blood vitamin D concentration was measured. The study results showed that eighty-four percent of black participants had vitamin D levels below 30ng/ml compared to 51% of whites. The average vitamin D level for black participants was 19.9. ng/ml compared to white participants with an average level of 28.2 ng/ml. Black participants reported increased overall knee osteoarthritis pain and those with lower vitamin D status displayed greater sensitivity to heat and pain.

The researchers commented that these data demonstrate that differences in pain sensitivity between the two races are mediated at least in part by variations in vitamin D levels. The scientists are now planning a study to investigate the impact of increased vitamin D levels on chronic pain in black and white older Americans.

Osteoarthritis involves degradation of the joints, causing joint pain, stiffness, tenderness, and locking. Vita-min D deficiency may be one of the many factors that account for increased pain in osteoarthritis. Although vitamin D deficiency is commonly defined as a 25-hydroxyvitamin D serum level below 20 ng/mL (50 nano-moles per liter), published studies have used different definitions for vitamin D deficiency. By using different cut-off points, vitamin D deficiency was found to be common in certain subpopulations, including older adults (41% using 25(OH)D level below 20 ng/mL), African Americans (61% using 25(OH)D level below 15 ng/mL), and women with osteoporosis (64% using 25(OH)D level below 30 ng/mL) (2).

1. Glover T. L. et al. Vitamin D, race, and experimental pain sensitivity in older adults with knee osteoarthritis. Arthritis & Rheumatism. Published online November 2012.
2. Forrest K. Y. Z. and Stuhldreher W. L. Prevalence and correlates of vitamin D deficiency in US adults. Nutrition Research. 2011; 31(1):48–54.