A comparative study of urinary sodium and potassium excretion in normotensive urban black and white South African males.

Increased sodium ingestion is regarded as a possible aetiological factor in chronic systemic hypertension. In order to assess dietary intake, the 24-hour urinary sodium and potassium excretions were measured in 71 Black (group 1) and 34 White (group 2) normotensive urban male factory workers, all of whom were aged between 30 and 50 years. The 24-hour urinary sodium excretion in group 1 (mean 126,8 mmol) was significantly lower than that in group 2 (mean 166,8 mmol). The mean 24-hour urinary potassium excretion in group 1 (30,9 mmol) was also significantly lower than that in group 2 (59,3 mmol). Our data have not confirmed the hypothesis that the salt intake of normotensive Blacks is higher than that of normotensive Whites. However, as a result of the surprisingly low potassium excretion in Blacks the estimated sodium/potassium ratio was significantly lower in group 2 (mean 2,9) than in group 1 (mean 4,3). This relatively high sodium/potassium ratio in Blacks may be a contributory factor in the development of systemic hypertension.