Body mass index time in target range and incident hypertension in middle-aged and older adults: a longitudinal study

Background This study aimed to determine the association of the time spent in the target range of body mass index (BMI) with the onset of developing hypertension. Methods This study used the longitudinal data from the China Health and Retirement Longitudinal Study (CHARLS), which consists of 4,369 residents who met the inclusion and exclusion criteria. Body Mass Index Time in Target Range (BMI-TTR) was defined as the number of times an individual's body mass index (BMI) fell within the target range (18.5 kg/m² ≤ BMI < 23 kg/m²) across three measurement waves (2011, 2013, and 2015). Based on these measurements, participants were systematically classified into four progressive categories: TTR1 (never in range) to TTR4 (always in range). Incident hypertension and time-to-event were identified during follow-up. The associations of BMI-TTR with hypertension were evaluated using multivariable Cox proportional hazards models, which used baseline BMI and other factors as confounding variables. Results In comparison to the TTR1 group, the risk of developing hypertension in the TTR4 group was significantly lower (adjusted hazard ratio [HR] = 0.717, 95% CI: 0.633–0.813, P  < 0.001). This inverse association persisted after additional adjustment for baseline BMI (HR = 0.718, 95% CI: 0.631–0.816, P  < 0.001). A significant inverse dose-response relationship was observed, with the incidence of hypertension decreasing progressively across higher BMI-TTR groups ( P for trend < 0.001). In women and in those aged 45–60 years, the protective association was more pronounced in the subgroup analyses. Furthermore, individuals whose BMI improved from out-of-range at baseline to within the target range at later visits had a similar risk reduction to those who maintained normal weight throughout. Conclusion Sustaining a BMI within the desired range over the long term is linked to a lower risk of developing hypertension in adults aged 45 and older, regardless of their initial BMI. This protective effect is particularly evident in women and middle-aged individuals. Our results highlight the significance of ongoing weight management in the primary prevention of hypertension.