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Body weight and osteoarthritis

  • Michael C Nevitt
    Affiliations
    Epidemiology and Biostatistics (MCN), University of California, San Francisco, San Francisco, California, USA
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  • Nancy Lane
    Correspondence
    Requests for reprints should be addressed to Nancy Lane, MD, Department of Medicine, University of California San Francisco, Box 0868, San Francisco, California 94143-0868
    Affiliations
    Department of Medicine (NL), University of California, San Francisco, San Francisco, California, USA
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      Osteoarthritis is the most common joint disorder, affecting over 25 million Americans, and one of the leading causes of disability among the elderly (
      • Lawrence R.C.
      • Helmick C.G.
      • Arnett F.C.
      • et al.
      Estimates of the prevalence of arthritis and selected musculoskeletal disorders in the United States.
      ). Pain during joint use, stiffness, and altered joint biomechanics contribute to loss of joint function and disability. Osteoarthritis of the knee and hip have the greatest effects, resulting in impaired mobility and lower extremity physical function and more than 250,000 joint replacements each year. Population surveys indicate that 10% to 13% of men and women aged 65 years and older have symptomatic knee osteoarthritis; nearly one third have radiographic findings. The prevalence of symptomatic osteoarthritis of the hip is about 3% to 5% in the elderly, and 10% of the elderly have radiographic hip osteoarthritis (
      • Felson D.T.
      The epidemiology of knee and hip osteoarthritis.
      ).
      Osteoarthritis is a slowly developing degenerative disease involving excessive breakdown and loss of articular cartilage, and proliferation and destruction of periarticular bone as a result of joint-specific abnormalities in biomechanics as well as general susceptibility due to age, genetic factors, and systemic and biochemical abnormalities (
      • Dieppe P.
      The classification and diagnosis of osteoarthritis.
      ). Both types of factors probably are responsible for the association between obesity and osteoarthritis in weight-bearing joints such as the knee and hip (
      • Felson D.T.
      • Chaisson C.E.
      Understanding the relationship between body weight and osteoarthritis.
      ). Excess weight increases the biomechanical load on these joints during weight-bearing activity. Forces across the knee and hip during walking and stair climbing, for example, are 2 to 4 times body weight. In addition, obesity may increase the risk of osteoarthritis because adiposity is associated with abnormal levels of hormones and growth factors, greater bone mineral density, and other metabolic intermediaries. Indeed, the association between obesity and osteoarthritis in non–weight-bearing joints is evidence for a systemic effect of adiposity.
      In this issue of the Journal, Gelber et al (
      • Gelber A.C.
      • Hochberg M.C.
      • Mead L.A.
      • et al.
      Body mass index in young men and the risk of subsequent knee and hip osteoarthritis.
      ) report findings from an investigation of osteoarthritis in the Johns Hopkins Precursor’s Study, a unique cohort of male former medical students who were examined in their 20s. Those who were overweight or obese (body mass index ≥25 kg/m2) as young men had a greater than threefold increased risk of developing symptomatic knee osteoarthritis by the time they reached their 60s compared with thin young men. Many previous studies have found a relation between obesity and knee osteoarthritis, but most have been cross-sectional (
      • Anderson J.
      • Felson D.T.
      Factors associated with osteoarthritis of the knee in the First National Health and Nutrition Examination Survey (NHANES I).
      ). More recently, prospective studies have demonstrated that being overweight increases the subsequent risk of new knee osteoarthritis, both symptomatic and radiographic, as well as worsening existing disease (
      • Manninen P.
      • Riihimaki H.
      • Heliovaara M.
      • Makela P.
      Overweight, gender and knee osteoarthritis.
      ,
      • Felson D.T.
      • Zhang Y.
      • Hannan M.T.
      • et al.
      Risk factors for incident radiographic knee osteoarthritis in the elderly.
      ,
      • Dougados M.
      • Gueguen A.
      • Nguyen M.
      • et al.
      Longitudinal radiologic evaluation of osteoarthritis of the knee.
      ). However, these studies have focused on the effect of obesity among middle-aged or elderly subjects, have studied only women, or have found that obesity was a much stronger risk factor for osteoarthritis in women than in men.
      The study by Gelber et al found a strong association between obesity and osteoarthritis in men. This association was present for weight and osteoarthritis assessed at younger ages than previously studied, suggesting that the lesser effect of obesity in men compared with women that has been seen in some studies may reflect the older age of the subjects in those studies. Gelber et al present evidence that being overweight during a man’s 20s had a larger effect on his subsequent risk of developing knee osteoarthritis than being overweight during his 40s. Perhaps this reflects a combined effect of certain physical activities and increased weight at younger ages, a question that is worthy of further study. Moreover, weight at age 20 years is correlated with weight in childhood and adolescence; Gelber et al speculate that damage to joints from overweight may occur even earlier, during skeletal growth and development. Physicians also may be less likely to suffer knee injury than men in other occupations, which would lower the incidence of knee osteoarthritis in the thinner subjects, thereby allowing the increased risk associated with being overweight to be observed.
      This study’s failure to find a relation between overweight and hip osteoarthritis is consistent with some, but not all, previous studies. Obesity in older subjects is weakly associated with unilateral hip osteoarthritis, but strongly related to bilateral hip osteoarthritis (
      • Felson D.T.
      • Chaisson C.E.
      Understanding the relationship between body weight and osteoarthritis.
      ), an endpoint not examined in the present study. Moreover, the Precursor’s Study cohort is relatively young for the occurrence of hip osteoarthritis, and the number of cases was small.
      Information about osteoarthritis in this study was based on self-report, which would be a major limitation in a study of the general population. However, physicians should be able to report their own diagnoses accurately, and effort was made to validate the diagnoses by obtaining additional details about symptoms and radiographic findings. An analysis including only those diagnoses corroborated by additional reports of knee pain and radiographic changes of osteoarthritis supported the main findings.
      There is both some good news and bad news in these findings. The good news is that weight is a modifiable risk factor. Felson and Chaisson (
      • Felson D.T.
      • Chaisson C.E.
      Understanding the relationship between body weight and osteoarthritis.
      ) and Felson and Zhang (
      • Felson D.T.
      • Zhang Y.
      An update on the epidemiology of knee and hip osteoarthritis with a view to prevention.
      ) have estimated that obesity is the number one preventable cause of knee osteoarthritis in women and ranks second in men after knee injury. Weight loss is recommended by the American College of Rheumatology for overweight patients with knee osteoarthritis (
      • Hochberg M.C.
      • Altman R.D.
      • Brandt K.D.
      • et al.
      Guidelines for the medical management of osteoarthritis I. Osteoarthritis of the hip.
      ). Several studies suggest that weight loss may reduce the symptoms and disability of knee and hip osteoarthritis (
      • Williams R.A.
      • Foulshen B.M.
      Weight reduction in osteoarthritis using phentermine.
      ,
      • Martin K.
      • Nicklas B.J.
      • Bunyard L.B.
      • et al.
      Weight loss and walking improve symptoms of knee osteoarthritis in overweight women with knee pain.
      ). Felson et al (
      • Felson D.T.
      • Zhang Y.
      • Anthony J.M.
      • et al.
      Weight loss reduces the risk for symptomatic knee osteoarthritis in women.
      ) found that older women who had lost about 5 kg during a 10-year period had a 50% reduction in the development of new symptomatic knee osteoarthritis. However, there are no randomized controlled trials of weight loss that show a reduction in knee or hip osteoarthritis.
      Unfortunately, the bad news has several dimensions. First, the increased risk reported by Gelber et al was found in men who had a body mass index greater than about 25 kg/m2, a much larger group of men than are currently defined as obese. Current clinical guidelines on the identification, evaluation, and treatment of overweight and obesity (
      NIH, NHLBI
      Clinical guidelines on the identification, evaluation and treatment of overweight and obesity in adults—the evidence report.
      ) classify a body mass index of 25 to 29.9 kg/m2 as overweight and a body mass index ≥30 kg/m2 as obese. Among men aged 20 to 39 years in the 1988–1994 NHANES III sample, 43% had a body mass index of 25 kg/m2 or greater. Second, despite increasing public awareness of the health risks associated with being overweight, the United States is in the midst of an epidemic of obesity involving all ages and nearly all racial and ethnic groups. Between 1960 and 1988, the proportion of men aged 20 to 29 years with a body mass index ≥30 kg/m2 increased 1.4-fold. Among women, the corresponding increase was even larger (
      NIH, NHLBI
      Clinical guidelines on the identification, evaluation and treatment of overweight and obesity in adults—the evidence report.
      ).
      Substantial weight reduction is difficult to achieve and maintain. Although a 10% weight loss over 6 months is a reasonable goal and is achieved by some, many obese individuals fail to lose weight when they try, regain weight after active intervention has ended, or do not try at all. The most effective interventions combine fat and caloric restriction, increased physical activity, behavioral reinforcement, and an extended weight maintenance program. Supplementary pharmocotherapy may also be appropriate and effective (
      NIH, NHLBI
      Clinical guidelines on the identification, evaluation and treatment of overweight and obesity in adults—the evidence report.
      ). Early intervention to prevent overweight children from becoming obese adults is clearly needed.
      The study by Gelber et al provides strong additional evidence that osteoarthritis of the knee, and its associated pain and disability, should receive greater recognition as an important health risk associated with being overweight or obese and as major contributors to the annual economic costs of this disorder (
      NIH, NHLBI
      Clinical guidelines on the identification, evaluation and treatment of overweight and obesity in adults—the evidence report.
      ). Because of the key role of increased physical activity in effective weight-loss programs, prevention and effective treatment of osteoarthritis are especially important in efforts to reduce the high prevalence of obesity in the United States. Randomized trials of weight loss interventions should include as outcomes knee and hip symptoms, as well as biological measures of osteoarthritis. Finally, when discussing the potential health benefits of weight loss with their obese patients, physicians should include prevention of osteoarthritis.

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