Being overweight is a clear risk factor for developing OA. Population-based studies have consistently shown a link between overweight or obesity and knee OA. Estimating prevalence across populations is difficult since definitions for obesity and knee OA vary among investigators. Data from the first National Health and Nutrition Examination Survey (HANES I) indicated that obese women had nearly 4 times the risk of knee OA as compared with non-obese women; for obese men, the risk was nearly 5 times greater. In a study from Framingham MA, overweight individuals in their thirties who did not have knee OA were at greater risk of later developing the disease. Other investigations, which performed repeated x-rays over time also, have found that being overweight significantly increases the risk of developing knee OA. It is estimated that persons in the highest quintile of body weight have up to 10 times the risk of knee OA than those in the lowest quintile.