Longitudinal Associations Between BMI, Physical Activity And Mortality Among Subjects With Coronary Heart Disease.

Abstract

PURPOSE: Obesity is a risk factor for coronary heart disease (CHD), but studies indicate that for subjects with established CHD the mortality risk is lower when body mass index (BMI) is above normal. Few studies exists on the joint effect of BMI and physical activity level on mortality in CHD. Our aim was to examine the independent and joint association of body mass index and physical activity with mortality in subjects with CHD, as well as the impact of longitudinal changes in BMI or physical activity on mortality risk. METHODS: We did a prospective cohort study with data from 5385 subjects with CHD from the Nord-Trøndelag Health study (HUNT) in 1984-1986, 1995-1997, or 2006-2008. Of these, 3515 participated in two or more HUNT waves. BMI was classified into 3 groups: normal weight(18.5-24.9 kg/m2), overweight (25.0-29.9 kg/m2), and obese (≥ 30 kg/m2). Change in BMI (in kg/m2/year) was categoriezed as loss (< -0.10), stable (-0.10 to 0.09), and gain (≥ 0.10). Physical activity level was categorized as inactive, low, or high. Low and high were merged in some analyses. Changes in physical activity were categorized as stable inactive, stable active, inactive-active, and active-inactive. The first five years of follow-up were excluded from the analysis. RESULTS: There were 2649 deaths during 25 (median 15.1) years of follow up. Compared to normal weight, the hazard ratio (HR) with (95% confidence interval (CI)) for mortality was for overweigth 0.91 (0.83-0.99), and for obese 0.95 (0.85-1.02). Low and high physical activity was associated with reduced mortality (HR: 0.88 (0.81-0.96) and 0.82 (0.74-0.92)), respectively. Compared to normal weight+inactive, obese+high had a HR of 0.62 (0.48-0.81). Overall, the HR for weight loss was 1.25 (1.07-1.44), compared to stable weight. For obese subjects, loss was not associated with increased risk, whereas weight gain was (HR: 1.38 (1.06-1.79). Compared to stable active, stabil inactive (HR: 1.47 (1.28-1.69) and active-inactive (HR: 1.25 (1.08-1.44) had increased risk, whereas inactive-active (HR: 1.13 (0.96-1.32) had not. CONCLUSION: Maintained or increased level of physical activity associated with improved survival in subjects with CHD. In obese, further weight gain was associated with increased risk, while for normal weight and overweight subjects weight loss was associated with risk.