Change in body mass index and its impact on blood pressure: a prospective population study.

BACKGROUND: Overweight and obesity increase the risk of elevated blood pressure, but the knowledge of the effect of weight change on blood pressure is sparse.

OBJECTIVE: To investigate the association between change in body mass index (BMI) and change in diastolic blood pressure (DBP), systolic blood pressure (SBP), and hypertension status.

DESIGN: Two population-based cross-sectional studies, one in 1984-86 and the other in 1995-97.

SETTING: The Nord-Trondelag Health Study (HUNT).

PARTICIPANTS: We included 15,971 women and 13,846 men who were 20 y or older at the first survey, without blood pressure medication at both surveys and without diabetes, cardiovascular disease or dysfunction in daily life at baseline.

MEASUREMENTS: Weight, height and blood pressure were measured standardised. Change in BMI was categorised as stable (initial BMI+/-0.1 kg/m2 each follow-up year), increased or decreased, and BMI was categorised by using World Health Organisation's categorisation (underweight BMI: <18.5 kg/m2, normal weight BMI: 18.5-24.9 kg/m2, overweight BMI: 25.0-29.9 kg/m2, obesity BMI> or =30 kg/m2).

RESULTS: An increase in BMI and a decrease in BMI were significantly associated with increased and decreased SBP and DBP, respectively, compared to a stable BMI in both genders and all age groups, although the strongest effect was found among those who were 50 y and older. The adjusted odds ratio for having hypertension at HUNT 2 was 1.8 (95% confidence interval (CI): 1.5, 2.2) among women and 1.6 (95% CI: 1.4,1.8) among men aged 20-49 y who increased their BMI compared to those who had stable BMI. A similar, but weaker association was found among women and men aged 50 y or more. The mean change in both SBP and DBP was higher for those who changed BMI category from first to the second survey than for those who were in the same BMI class at both surveys.

CONCLUSIONS: Our result supports an independent effect of change in BMI on change in SBP and DBP in both women and men, and that people who increase their BMI are at increased risk for hypertension.