Relationship of Meeting Physical Activity Guidelines and Quality Adjusted Life Years

Background/Purpose Regular physical activity is associated with reduced chronic disease burden and mortality. Recognizing the importance of physical activity, there are US federal guidelines for adults that also include persons with arthritis. Improving physical activity may be key to improving overall public health and reducing health care spending. Quality Adjusted Life Year (QALY) is a standard outcome measure used in cost-effectiveness analyses. We analyzed the data from the Osteoarthritis Initiative (OAI) to determine whether increasing levels of physical activity is correlated to larger QALY estimates.

Methods Physical activity was measured using accelerometers and was classified as 1) Meeting Guidelines (≥150 moderate-to-vigorous [MV] minutes/week acquired in bouts ≥10 minutes); 2) Insufficiently Active (some but <150 MV bout minutes/week) or 3) Inactive (no bouts of MV activity lasting 10 minutes over the week). An SF6-D utility score (range 0-1) was derived from patient reported health status at baseline and 2 year follow-up. The QALY outcome was calculated as the area under utility curve over 2 years (range 0-2). Data were stratified by gender and body mass index (BMI). The relationship of physical activity levels to median QALY adjusted for sociodemographic factors (age, gender, race, education, income) and clinical/health factors (body mass index, medical comorbidity, smoking, presence of radiographic knee osteoarthritis, knee symptoms, and prior knee injury) was derived using median quantile regression.

Results Median QALYs over 2 years were significantly higher with greater physical activity level in a stepwise fashion as shown by the cumulative frequency curve (figure). Relative to the Inactive group, the median QALYs of the Meeting Guidelines group was 0.162 (95% confidence interval (CI) 0.120-0.204)higher, and that of the Insufficiently Active group was 0.082 (95% CI 0.052-0.110) higher. After adjusting for sociodemographic and clinical/health factors, the differences in median QALYs continued to show a statistically significant linear trend with physical activity level. Similar findings were observed when the cohort was stratified by gender and BMI.

Conclusion We found a strong graded relationship between greater physical activity and better QALYs. Moving individuals from the Inactive to Insufficiently Active group or from the Insufficiently Active to Meeting Guidelines group could be associated with a 0.08 increase in QALYs over 2 years. An intervention costing $4,000 or less that resulted in such physical activity gains would be cost effective using a $50,000 per QALY gain cutoff. Our analysis further supports the potential effectiveness and cost- effectiveness of interventions to promote physical activity even if recommended levels are not fully attained.