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 themost common nutritional deficiency worldwide withmore than 40% of the adult population of over50 years of age being vitamin D deficient.1 Similarly,osteoarthritis (OA) is the most common joint disorderin adults around the world with nearly 3.8% of the globalpopulation affected by knee OA and 0.85% affectedby hip OA.2 Prevalence of OA in 2010 was highest inthe Asia-Pacific high-income region, followed by Oceaniaand North Africa/Middle East.2 The prevalence ofvitamin D deficiency and OA increases significantlywith age and is higher in women and in the obesepopulation.