Impact of obesity on incident hypertension independent of weight gain among nonhypertensive Japanese: the Ibaraki Prefectural Health Study (IPHS)

Objective: The aim of this study was to examine the association between BMI and risk of incident hypertension among Japanese men and women who are middle-aged and older. Design: Prospective, population-based cohort study. Patients: A total of 68 205 nonhypertensive adults ( 18 336 men and 49 869 women) aged 40-79 years who completed health check-ups in the Ibaraki prefecture, Japan, in 1993 were followed up through 2006. To exclude the impact of BMI change during the follow-up period, a time-dependent covariate Cox proportional hazards model was used to compute the hazard ratios of incident hypertension according to BMI categories. Incident hypertension was defined as a SBP of at least 140 mmHg, a diastolic BP of at least 90 mmHg, and/or hypertensive medication use. Results: A total of 30 982 adults ( 45.4%) developed hypertension ( 9331 men and 21 651 women) during a mean of 3.9 years of follow-up. Compared with a BMI of less than 19.0, time-dependent covariates adjusted hazard ratios [95% confidence interval (CI)] for hypertension among participants with a BMI of at least 25.0 were 1.42 (1.17-1.73) for men aged 40-59 years, 1.34 (1.19-1.51) for men aged 60-79 years, 1.47 (1.33-1.62) for women aged 40-59 years, and 1.29 (1.18-1.41) for women aged 60-79 years. Conclusion: The baseline BMI is associated with future risk for incident hypertension even after accounting for weight change during the follow-up period. Weight loss may be recommended to nonhypertensive obese adults to prevent the development of hypertension.