Vitamin D and osteoarthritis: disparity between observational studies and clinical trials

Vitamin D deficiency (defined as serum level of 25-hydroxyvitamin D [25-(OH)D] < 50 nmol/L) is the most common nutritional deficiency worldwide with more than 40% of the adult population of over 50 years of age being vitamin D deficient. Similarly, osteoarthritis (OA) is the most common joint disorder in adults around the world with nearly 3.8% of the global population affected by knee OA and 0.85% affected by hip OA. Prevalence of OA in 2010 was highest in the Asia-Pacific high-income region, followed by Oceania and North Africa/Middle East. The prevalence of vitamin D deficiency and OA increases significantly with age and is higher in women and in the obese population.