Association and Time-Varying Effects of Body Mass Index on All-Cause Mortality in Patients With Hypertension

Abstract BackgroundThe relationship between body mass index (BMI) and mortality in hypertension patients remains controversial. This study aimed to evaluate the association and the time-varying effects of different BMI categories on the risk of all-cause mortality in hypertension patients. MethodsThis retrospective cohort study was conducted among 212,394 Chinese people with hypertension. All deaths were identified based on Shanghai Vital Statistics. Cox model combined with time-by-covariate interactions was used to estimate the association and the time-varying effects of BMI on the risk of all-cause mortality. The potential non-linear effects across follow-up period for BMI were examined by the application of restricted cubic spline (RCS).ResultsOverall, 31,130 deaths occurred (14.7%) within an average follow-up of 8.24 years. Underweight (<18.5 kg/m2) showed a progressively weakening negative effect on all-cause mortality over time. For both sexes, overweight (23.0-24.9 kg/m2) and class I obesity (25.0-29.9 kg/m2) showed protective effects within 5 years after registration, but these became insignificant in later years. There was no significant difference in the effect on all-cause mortality between class II obesity (≥30.0 kg/m2) and normal weight. in the elderly patients, overweight, class I obesity and class II obesity had continuous protective effects on mortality.ConclusionsAlthough the effect of baseline body mass index on the risk of all-cause mortality varied at different follow-up periods, underweight persistently remained a risk factor for all-cause mortality in hypertension, whereas overweight and class I obesity had protective effects. Thus, in the long-term management of hypertension, more attention should be given to underweight patients.