Sodium excretion and racial differences in ambulatory blood pressure patterns

The influence of Na⁺ excretion and race on casual blood pressure and ambulatory blood pressure patterns was examined in a biracial sample of healthy, normotensive children and adolescents (10-18 years; n=140). The slopes relating 24-hour urinary Na⁺ excretion to systolic blood pressure were different for both black and white subjects for casual blood pressure (p<0.001) and blood pressure during sleep (p<0.03). For casual blood pressure, the slope was significant for black subjects (β=0.17; p<0.001) but not for white subjects. For blood pressure during sleep, the slope was again significant for black subjects (β=0.08; p<0.01) but not for white subjects. Na⁺ excretion was also related to awake levels of systolic blood pressure for black subjects (β=0.08, r=0.36; p<0.01), although the slopes for both black and white subjects were not significantly different. Further analyses indicated the results were not due to racial differences in 24-hour urinary K⁺ excretion. However, plasma renin activity was marginally related to Na⁺ excretion in white subjects (r=0.22; p<0.06) but not black subjects, a finding that is consistent with previous studies. Na⁺ excretion was not associated with diastolic blood pressure or heart rate in either group under any condition. The results of this study support research that has demonstrated a stronger relation between Na⁺ handling and casual blood pressure in black subjects and extend these findings to blood pressure while the subject is both awake and asleep.