Individual and joint effects of red blood cell traits on hypertension: a longitudinal analysis

Previous reports found positive associations between red blood cell (RBC) traits (RBC count and hemoglobin) and hypertension, but their individual and joint effects on new-onset hypertension by sex are unclear.

This longitudinal study involved 51 663 adults from the Kailuan Cohort. We utilized weighted Cox regression models to evaluate the individual and joint effects of RBC count and hemoglobin on new-onset hypertension by sex. Restricted cubic splines regression and Kaplan-Meier curves were employed to evaluate the non-linear relationships and depict the differential survival probabilities, respectively. In the longitudinal analysis regarding individual effects, we found positive associations between RBC count and hemoglobin with new-onset hypertension in both men and women. As for joint effects, we discovered that subjects with higher RBC counts than the median but lower hemoglobin values than the median, labelled as RBC (+) and hemoglobin (-), had a higher risk of hypertension in women [hazard ratio (HR) = 1.19, 95% confidence interval (CI): 1.02-1.39] compared with those categorized as RBC (-) and hemoglobin (-), yet not in men. Additionally, subjects with lower RBC values than the median but higher hemoglobin values than the median, denoted as RBC (-) and hemoglobin (+), exhibited an increased risk of hypertension in men (HR = 1.12, 95% CI: 1.06-1.18) compared with those classified as RBC (-) and hemoglobin (-), but not in women. These findings were consistent in sensitivity and cross-sectional analyses.

Our findings suggest that RBC count primarily plays a role in women's hypertension, while hemoglobin mainly affects hypertension in men.