Objective: To investigate body mass index (BMI) and weight change in relation to risk for hypertension.

Design: Cohort study.

Setting: General community.

Participants: Cohort of 82 473 U.S. female nurses 30 to 55 years of age followed every 2 years since 1976. The follow-up rate was 95%.

Measurements: Primary risk factors examined were 1) BMI at age 18 years and midlife and 2) long-term and medium-term weight changes. The outcome was incident cases of hypertension.

Results: By 1992, 16 395 incident cases of hypertension had been diagnosed. After adjustment for multiple covariates, BMI at 18 years of age and midlife were positively associated with occurrence of hypertension (P for trend < 0.001). Long-term weight loss after 18 years of age was related to a significantly lower risk for hypertension, and weight gain dramatically increased the risk for hypertension (compared with weight change less than or equal to 2 kg, multivariate relative risks were 0.85 for a loss of 5.0 to 9.9 kg, 0.74 for a loss greater than or equal to 10 kg, 1.74 for a gain of 5.0 to 9.9 kg, and 5.21 for a gain greater than or equal to 25.0 kg). Among women in the top tertile of baseline BMI at age 18 years, weight loss had a greater apparent benefit. The association between weight change and risk for hypertension was stronger in younger (<45 years of age) than older women (greater than or equal to 55 years of age). Medium-term weight changes after 1976 showed similar relations to risk for hypertension.

Conclusions: Excess weight and even modest adult weight gain substantially increase risk for hypertension. Weight loss reduces the risk for hypertension.