Osteoarthritis is the most common joint disease, a degenerative condition in which the cartilage cushioning the joints breaks down, leaving bones to grind painfully. It typically affects the knees, hips, hands, and spine from middle age onward, causing stiffness, swelling, and reduced mobility that worsens with use. Excess body weight is the strongest modifiable risk factor, since every extra kilogram multiplies the load on knee joints and adipose tissue releases inflammatory mediators. Nutritional management focuses on weight loss where needed, adequate vitamin D and calcium for the underlying bone, and anti-inflammatory dietary patterns rich in vegetables, fruit, oily fish, and olive oil. Glucosamine and chondroitin supplements are popular but the evidence for meaningful benefit is weak. Exercise that strengthens supporting muscles remains the most effective non-drug intervention.