Body mass index in young men and the risk of subsequent knee and hip osteoarthritis

PURPOSE: Obesity in middle age is associated with an increased risk of oste oarthritis of the knees in later life. We sought to determine whether body mass index in young men was a risk factor for the subsequent development of osteoarthritis of the knee and hip. SUBJECTS AND METHODS: Body mass index was assessed in 1,180 male medical st udents at age 23 +/- 2 (mean +/- SD) years and at several times during foll ow-up. The incidence of knee and hip osteoarthritis was ascertained by self -report and corroborated with information on symptoms and radiographic find ings. RESULTS: During a median follow-up of 36 years, 62 participants developed k nee osteoarthritis and 27 developed hip osteoarthritis. The incidence of kn ee, but not hip, osteoarthritis was strongly associated with body mass inde x assessed at ages 20 to 29 pears and 30 to 39 years (both P <0.001). For b ody mass index assessed at ages 20 to 29 years, the incidence of knee osteo arthritis at age 65 years was 12.8% among the heaviest subjects (range 24.7 to 37.6 kg/m(2)), threefold greater than the incidence of 4.0% in the lean est (15.6 to 22.8 kg/m(2)) category of body mass index (P = 0.0001). Thus, for a man who was 180 cm (5' 11") tall, each 8 kg(18 Ib) greater weight at ages 20 to 29 years was associated with an increased risk of subsequent kne e osteoarthritis (relative risk = 1.7, 95% confidence interval 1.3 to 2.1), after adjustment for year of birth, physical activity, and knee injury. Bo dy mass index at ages 20 to 29 years was more predictive of future osteoart hritis than at ages 30 to 39 or 40 to 49 years. CONCLUSION: Greater body mass index in young men ages 20 to 29 years is ass ociated with an increased risk of subsequent knee, but not hip, osteoarthri tis, suggesting that cumulative exposure to greater weight during young adu lt life is an important cause of osteoarthritis. Am I Med. 1999;107:542-548 . (C) 1999 by Excerpta Medica, Inc.