White blood cell count and hypertension incidence. The NHANES I Epidemiologic Follow-up Study

To test the hypothesis that elevated white blood cell count (WBC) is associated with increased incidence of essential hypertension, data from the NHANES I Epidemiologic Follow-up Study (NHEFS) were analyzed. Incidence of hypertension was determined in a cohort of 5782 white and 674 black persons with complete data who were normotensive at baseline. There was a statistically significant increase of about 50% in risk of hypertension over approximately 10 years' follow-up in white men aged 25-74 years with WBC > 8600 compared to men with WBC < 6200 cells/mm3. The association was independent of other risk variables. In white women, an association of high WBC with increased age-adjusted risk of hypertension was seen only at ages 45-64 and 65-74 years. The association was diminished and no longer significant after controlling for multiple risk variables. Data for black women suggested an increased risk among women with higher WBC compared to those with lower WBC at ages 65-74 after controlling other risk variables (p = 0.0001). No positive association was seen in black men. Thus, data from NHEFS confirm the previously reported association of higher WBC with increased incidence of hypertension in white men, and possibly older white and black women. Given the lack of a compelling biological explanation, further studies of this association are needed, especially in women and blacks.