Distribution of sodium-lithium countertransport and blood pressure in Caucasians five to eighty-nine years of age.

Abstract

Case-control studies suggest that increased erythrocyte sodium-lithium countertransport may predict increased susceptibility to the development of essential hypertension. To characterize interindividual variation in sodium-lithium countertransport and its relation to blood pressure levels in the general population, we studied 1,475 Caucasians between 5 and 89 years of age (711 males and 764 females) ascertained through 266 households with children in the schools of Rochester, Minnesota. Individuals who were taking antihypertensive agents or combinations of estrogen and progesterone were not included in the sample. A third-order polynomial regression on age accounted for only a small fraction of variability in sodium-lithium countertransport (2.8% in males, p less than 0.001; 2.1% in females, p less than 0.01), whereas a fourth-order regression on age accounted for a large proportion of variability in systolic blood pressure (45.7% in males, p less than 0.001; 52.5% in females, p less than 0.001) and diastolic blood pressure (39.8% in males, p less than 0.001; 33.0% in females, p less than 0.001). Mean sodium-lithium countertransport was higher in males than females at all ages; but the rank order of male and female means for systolic and diastolic blood pressure was age dependent. Positively skewed distributions for age-, height-, and weight-adjusted sodium-lithium countertransport in male and female cohorts between 5-19.9, 20-49.9, and 50-89.9 years of age were explained significantly better by postulating a mixture of two partially overlapping sodium-lithium countertransport distributions rather than a single normal distribution (p less than 0.01). Among men in the 20-49.9-year-old cohort, adjusted sodium-lithium countertransport values in the upper distribution were associated with higher systolic and diastolic blood pressure (mean +/- SD) than values in the lower distribution (for systolic blood pressure: 115 +/- 11 vs. 111 +/- 11 mm Hg, p less than 0.07; for diastolic blood pressure: 71.2 +/- 8.0 vs. 68.4 +/- 8.6 mm Hg, p less than 0.08). Among females in the 50-89.9-year-old cohort, adjusted sodium-lithium countertransport values in the upper distribution were associated with significantly greater diastolic blood pressure than values in the lower distribution (77 +/- 10 vs. 70 +/- 9 mm Hg, p less than 0.03).(ABSTRACT TRUNCATED AT 400 WORDS)