Prehypertension, obesity, and risk of kidney disease: 20-year follow-up of the HUNT I study in Norway.

BACKGROUND: The combined effect of blood pressure (BP) and body weight on risk of kidney disease has not been previously studied. To improve risk stratification in prehypertensive individuals (ie, BP, 120 to 139/80 to 89 mm Hg), we examined the interaction between BP and body weight on the risk of end-stage renal disease or chronic kidney disease (CKD)-related death.

STUDY DESIGN: Retrospective cohort study.

SETTING & PARTICIPANTS: 74,986 adults participating in the first Health Study in Nord-Trøndelag (88% participation rate) were linked to the Norwegian Renal Registry and Cause of Death Registry.

PREDICTORS: BP and body weight were measured by using standard procedures, and other relevant covariates were obtained from an extensive questionnaire.

OUTCOME & MEASUREMENTS: Hazard ratios for treated end-stage renal disease and CKD-related death were calculated.

RESULTS: Mean systolic BP and body mass index (BMI) were 136.8 +/- 23.3 (SD) mm Hg and 25.2 +/- 3.9 kg/m(2), whereas 12.9% had treated hypertension at baseline, respectively. During a median follow-up of 21 years (1,345,882 person-years), 507 men (1.4%) and 319 women (0.8%) initiated renal replacement therapy (n = 157) or died of CKD (n = 669). Multiadjusted risk of these kidney outcomes increased continuously with no lower threshold for BP. The risk associated with body weight started to increase from a BMI of 25.0 kg/m(2). In participants with BP less than 120/80 mm Hg, risk did not increase with increasing BMI. In prehypertensive participants, multivariate adjusted hazard ratios in the BMI categories 18.5 to 24.9, 25.0 to 29.9, 30.0 to 34.9, and 35.0 kg/m(2) or greater were 1.21 (95% confidence interval [CI], 0.67 to 2.17), 1.10 (95% CI, 59 to 2.00), 2.66 (95% CI, 1.28 to 5.53), and 5.94 (95% CI, 1.94 to 18.20) compared with BP less than 120/80 mm Hg and BMI of 18.5 to 24.9 kg/m(2), respectively (P = 0.02 for trend). Corresponding risks in hypertensive participants were 2.13 (95% CI, 1.23 to 3.70), 2.40 (95% CI, 1.40 to 4.15), 3.32 (95% CI, 1.89 to 5.81), and 5.53 (95% CI, 3.01 to 10.20), respectively (P < 0.001 for trend).

LIMITATIONS: Baseline creatinine measurements were not available; hence, a secondary analysis was performed that excluded all individuals who experienced outcomes in the 5 years after the study start.

CONCLUSIONS: Participants with prehypertension are not at increased risk of serious kidney outcomes if BMI is less than 30.0 kg/m(2). However, the risk of kidney disease increases substantially if prehypertension is present in obese participants.