We estimated that roughly 86 million quality-adjusted life-years, comprising 8.4% of remaining quality-adjusted life expectancy, were lost over the remaining lifespan of a cohort of persons aged 50 to 84 years owing to obesity, symptomatic knee osteoarthritis, or both. These conditions affect 40% of the 85 966 369 U.S. citizens in that age range. We estimated that 12% of these losses were attributed to knee osteoarthritis and 88% to obesity. Black and Hispanic women were disproportionately affected by osteoarthritis and obesity and consequently had the greatest percentage of quality-adjusted life-years lost in comparison with their population size.
Symptomatic knee osteoarthritis and obesity probably influence quality-adjusted life-year losses through different mechanisms. Obesity affects quality of life; is an independent risk factor for mortality; and is associated with higher prevalence and incidence of diabetes mellitus, coronary heart disease, and other comorbid conditions that reduce survival (9
). Thus, obesity reduces both quality and quantity of life (13
). Symptomatic knee osteoarthritis does not directly affect mortality but considerably reduces quality of life, thereby diminishing quality-adjusted life expectancy (18
). The racial and ethnic differences in quality-adjusted life expectancy in our model stem primarily from differential rates of knee osteoarthritis, coronary heart disease, diabetes mellitus, and cancer, as well as differences in underlying age- and sex-adjusted mortality.
The effect of symptomatic knee osteoarthritis on quality of life is similar to that of metastatic breast cancer and other disabling conditions (51
). Obesity, independent of knee osteoarthritis, reduces life expectancy considerably (5
). Few studies have focused on the effect of obesity on quality of life. One study established that obesity is associated with poor quality of life and that joint pain, as well as obesity-related comorbid conditions, mediates the relationship between BMI and quality of life (55
). Another study found that obesity is associated with diminished quality of life, even after adjustment for age, sex, and comorbid conditions (56
). These findings were limited by the cross-sectional nature of both studies.
Several studies have shown that knee osteoarthritis is more prevalent in women than in men (7
). The Framingham Osteoarthritis Study (57
) showed that increased weight in women elevated their risk for knee osteoarthritis. One study found that black women had greater risk for knee osteoarthritis, even after adjustment for age and BMI (21
). Another study documented a nearly 3-fold greater prevalence of radiographically defined osteoarthritis in black versus white women (59
). Our estimates showing disproportionate quality-adjusted life-year losses for black women are consistent with other findings (60
The unique nature of our study lies in its ability to account for the multidimensional nature of disease burden, expressed as quality-adjusted life-year losses. Our approach allowed us to synthesize both mortality attributable to obesity and major comorbid conditions, as well as the diminished quality of life owing to knee osteoarthritis, obesity, and other comorbid conditions. Furthermore, we estimated attribution of quality-adjusted life-years lost owing to knee osteoarthritis and obesity in persons affected by both conditions. By linking per-person losses in quality-adjusted life expectancy to population size, we were able to estimate total quality-adjusted life-years lost for the entire population.
Our estimates show that reducing the mean BMI to levels experienced a decade ago in adults aged 50 to 84 years would yield substantial health benefits. Evidence suggests such changes in BMI are achievable and sustainable (49
Our study had several limitations. In modeling studies, the validity, precision, and completeness of input data may have important consequences for study findings. The OAPol Model input parameters were derived from several sources. Regular literature searches were conducted to identify the most current data. When newer data were not available, validation and calibration analyses were conducted by comparing model-based projections against data from external sources. When confronted with a choice of model inputs, we chose inputs that would lead to more conservative estimates of quality-adjusted life-expectancy losses. In the absence of longitudinal cohort data, prevalence estimates were converted to incidence on the basis of life expectancy of the general population, potentially resulting in conservative underestimates of incidence rates. The simplified approach used to estimate increased mortality among persons with several conditions is conservative because it avoids overestimating mortality. We based our estimates of symptomatic, radiographic osteoarthritis incidence on data that used cases diagnosed by a physician, making these estimates conservative. We did not include the effect of bariatric surgery—the obesity treatment method with the most substantial effects. Because bariatric surgery is done primarily in morbidly obese persons, this omission probably did not meaningfully influence our estimates. Although Asian Americans represent a growing proportion of the overall population, they are least affected by obesity and knee osteoarthritis, and data on the prevalence of comorbid conditions in Asian Americans (stratified by age and sex) are sparse. Thus, we did not include Asian Americans in our estimates.
Our model-based estimates suggest that among the 86 million persons aged 50 to 84 years in the United States, approximately 40% have symptomatic osteoarthritis, are obese, or both. These conditions result in 86 million quality-adjusted life-years lost among U.S. adults aged 50 to 84 years. Obesity reduces the remaining quality-adjusted life expectancy in obese persons by about 12% across all age groups, whereas osteoarthritis reduces the remaining quality-adjusted life expectancy in persons with knee osteoarthritis by about 13% in persons who are in their 50s and 10% in persons in their 70s. These findings underscore the importance of incorporating measures of quality of life in estimating the burden of these conditions. The disproportionate burden these conditions impose on black and Hispanic women suggests that future studies should investigate tailoring prevention and treatment strategies to sex and racial or ethnic subpopulations. With 86 million quality-adjusted life-years at stake and the incidence of knee osteoarthritis and obesity increasing, the potential public health effect of successful interventions to prevent these conditions is very substantial and worthy of intensive investigation.