There is a clear link between being overweight and being more likely to experience joint pain in the hands, knees, hips, back and neck.
Medical researchers don't know why exactly the excess weight leads to a higher incidence of osteoarthritis. The extra weight would increase the load placed on joints such as knees and hips and could speed up the breakdown of cartiledge. But overweight people are also more likely to suffer from hand arthritis so there must be more to the connection - perhaps something which involves the circulating systemic factor as well.
Obese women have four times the risk of knee osteoarthritis as non-obese women. Obese men are five times as likely to suffer from knee osteoarthritis. Studies have found that even small amounts of weight loss can reduce the risk of developing knee OA and that weight loss decreases knee pain substantially.
For more information about the relationship between osteoarthritis and body weight, see the John Hopkins page on Arthritis.