A study of urinary sodium and potassium excretion rates among urban and rural Zulus and Indians.

A study was carried out to evaluate the relationship between blood pressure, plasma renin activity, serum aldosterone and patterns of urinary sodium and potassium excretion rates in urban Zulus, rural Zulus and Indians in order to explain the high prevalence of hypertension in the urban adult Zulu (25%) compared to the rural adult Zulu (10%). Urinary sodium and potassium were not significantly different between urban and rural Zulus. There was no association between sodium excretion and blood pressure. Urinary potassium correlated negatively with blood pressure in rural Zulus and Indians but not in urban Zulus. The urinary sodium:potassium ratio was significantly lower in rural Zulus than in urban Zulus. The sodium:potassium ratio of Indians was not significantly different from that of Zulus. Plasma renin activity levels were significantly lower in urban than in rural Zulus. This difference is an enigma but may be due to an environmental factor. Serum aldosterone correlated positively with plasma renin activity and negatively with the urinary sodium:potassium ratio.