Vitamin D Supplementation in Knee Osteoarthritis

Knee osteoarthritis (OA) is a degenerative joint condition and a leading contributor to the global burden of disease. Estimates indicate that approximately 14 million people in the United States have symptomatic knee OA, and nearly half of those individuals are between 45 and 65 years of age. Over the years, data have extended our knowledge regarding the early premise of knee OA being the sole consequence of "wear and tear" processes of articular cartilage and it is now recognized that knee OA arises, in part, as a consequence of cytokine-mediated cellular and signaling events.

Cytokines are pleiotropic proteins instrumental to the immune response, host defenses, and intra- and inter-cellular signaling. Tumor necrosis factor (TNF)-α and interleukin (IL)-1β are pro-inflammatory cytokines that promote the catabolic and destructive events of knee OA in animal and human studies. These findings are corroborated by data illustrating chondrocytes as a site for pro-inflammatory cytokine production in knee OA, and that disease severity and progression associate with increasing TNF-α, IL-1β, and other cytokine concentrations in the circulation and transcriptional expression in peripheral blood leukocytes. Fortunately, IL-10 is an anti-inflammatory cytokine expressed in chondrocytes and possesses chondroprotective properties by inhibiting pro-inflammatory cytokine production. While some factors are unavoidable or unpreventable, such as aging, trauma, and genetic predisposition, disrupting the cytokine network could alter OA development and progression.

Low circulating vitamin D concentrations are reported in elderly with and without knee osteoarthritis symptoms. Serum 25(OH)D concentrations associate with muscular strength or performance in elderly. Vitamin D supplementation increases serum 25(OH)D concentrations and improves muscular strength in elderly. Based on these observations, vitamin D is essential for muscle function in elderly, however, it is unknown if supplemental vitamin D influences muscular strength in subjects with knee OA. Furthermore, it is probable that a more comprehensive supplement is necessary to improve muscular strength.

The aim of this study is to identify the influence of supplemental vitamin D on circulating cytokines and muscular strength in subjects with knee OA. This study consists of a double-blind, placebo-controlled experimental design. Subjects will be randomly assigned to one of three groups: (#1) vitamin D (cholecalciferol, 4000 IU) with glucosamine sulfate (1000 mg) and omega-3 fatty acids (eicosapentaenoic (EPA, 580 mg) and docosahexaenoic (DHA, 470 mg) acids), (#2) vitamin D (cholecalciferol, 4000 IU) with matching glucosamine sulfate and omega-3 fatty acid placebo supplements, or (#3) matching vitamin D, glucosamine sulfate and omega-3 fatty acid placebo supplements. Supplements will be taken daily for 84 days (12 weeks). Groups will be permutated in random blocks of six. Serum 25(OH)D, serum cytokines and muscular-based outcomes will be determined prior to, during, and following supplementation.

Inclusion criteria

• Unilateral knee pain, weakness, and impaired physical activity
• Older than 18 years of age but younger than 60 years of age
• Reportedly physically active (minimum of 30 minutes of continuous exercise or physical exertion 3 times per week during the previous year)

Exclusion criteria

• Bilateral symptoms of hip, knee or ankle osteoarthritis
• Recent (within 2 years) surgery on the symptomatic or non-symptomatic limb
• History of metabolic bone disease
• History of any skeletal muscle pathologies
• History of cardiac or peripheral cardiovascular system abnormalities
• History of clotting disorders
• History of coronary artery disease, peripheral vascular disease, or stroke
• History of cancer
• Use of warfarin or other anti-coagulants prior to study enrollment
• Use of cholesterol lowering medication
• History of high cholesterol or triglycerides
• History of high blood pressure
• Diagnosed with diabetes mellitus
• Impaired liver function
• Impaired kidney function
• Pregnant
• Daily dietary supplement or vitamin use during the previous year
• Use of corticosteroid medication
• Use of orlistat, phenobarbital, phenytoin, or thiazide
• Morbidly obese (body mass index > 40 kg/m2)