Increased predictive ability of BMI but not other risk factors with time in men: 39-year follow-up of total mortality in the Oslo study

Abstract

Objective: Risk factor associations to mortality may change, in part due to removal of highrisk persons. We compared strengths of association and ability of risk factors to predict total mortality across short (<15 years), medium (15-29 years) and long (30-39 years) follow-up. Methods: Cardiovascular risk factors were measured in 1972-1973 in the Oslo Study among 14,846 men born in 1923-1932. Relationships of risk factors to mortality (to 2011) were analyzed using Cox regression models, and receiver operating characteristics (ROC) were estimated. Results: BMI was the only factor that increased strength of association with elapsed time (hazard ratio for ≥ 35 kg/m2v2. 22.5-24.9 kg/m2: 1.25 (95% CI 0.73-2.17), 1.51 (95% CI 1.06-2.16) and 3.73 (95% CI 2.33-5.98) for <15, 15-29 and 30-39 years, respectively). Other factors lost predictive ability with time. Cigarette smoking was the strongest predictor in all periods. Serum lipids and systolic blood pressure increased risk in most periods, and moderate physical activity was protective to 29 years, but these factors and BMI contributed minimally to ROC. Discussion: Risk factors differed in association strengths and ability to predict mortality over four decades. BMI strengthened its association with time, while cigarette smoking was strongest in all periods.