Physical activity and self-reported, physician-diagnosed osteoarthritis

Abstract

This prospective study evaluated regular physical activity and self-reported physician-diagnosed osteoarthritis of the knee and/or hip joints among 16,961 people, ages 20–87, examined at the Cooper Clinic between 1970 and 1995. Among those aged 50 years and older, osteoarthritis incidence was higher among women (7.0 per 1000 person-years) than among men (4.9 per 1000 person-years, P = 0.001), while among those under 50 years of age, osteoarthritis incidence was similar between men (2.6) and women (2.7). High levels of physical activity (running 20 or more miles per week) were associated with osteoarthritis among men under age 50 after controlling for body mass index, smoking, and use of alcohol or caffeine (hazard ratio = 2.4, 95% CI: 1.5, 3.9), while no relationship was suggested among women or older men. These findings support the conclusion that high levels of physical activity may be a risk factor for symptomatic osteoarthritis among men under age 50.

Introduction

Osteoarthritis of the hip and knee represent two of the most important causes of pain and physical disability in community-dwelling adults 1, 2. This condition can be classified into two types: primary osteoarthritis (OA) is generally related to aging and heredity [3] while the specific etiology is not clear; secondary OA is caused by other diseases or conditions such as obesity, joint trauma, or repetitive joint use 3, 4, 5, 6, 7, 8. In addition, Hart et al. [9] found that hypertension, hypercholesterolemia, and high blood glucose are associated with both unilateral and bilateral knee OA independent of obesity and suggested that OA had an important systemic and metabolic component in its etiology.

While many types of physical activity involve repetitive joint use that may cause cartilage attrition, physical activity should be helpful in preventing OA in several ways. First, physical activity strengthens the muscular support around joints and thereby reduces the risk of joint injury. Second, physical activity prevents the joints from ‘freezing up’ and improves and maintains joint mobility. Third, physical activity helps to avoid obesity, a risk factor for some forms of OA. Finally, because cartilage has no blood vessels or nerves, mature cartilage cells receive nourishment only from the diffusion of substances through the cartilage matrix from joint fluid, and physical activity enhances this process [10]. However, persons who participate in competitive sports and certain types of occupational activity have been shown to be at higher risk for OA 11, 12, 13.

Regular physical activity is increasingly recognized as a major protective factor for coronary heart disease as well as a variety of related health benefits [14]. In the United States and other developed countries public health efforts are under way to encourage regular physical activity. Because leisure-time physical activity is widely promoted as a way to improve and maintain health, it is important to understand its potential effect on OA. There are a number of studies on the role of physical activity in the development of OA 5, 6, 7, 8, 9, 13, 15, 16, 17, 18, but the results are inconclusive. The purpose of this prospective study is to evaluate the association between physical activity and the incidence of self-reported physician-diagnosed OA, while controlling for other potential risk factors such as age, gender, body weight, current and past smoking, and consumption of alcohol and caffeine.