A Study of 48-Hour Faecal and Urinary Electrolyte Excretion in Normotensive Black and White South African Males

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Previous studies have shown that 24-h urinary sodium (Na) excretion is similar in blacks and in whites. However, a significantly lower potassium (K) excretion by blacks, with a consequent rise in the Na:K excretion ratio, has been observed. Faecal electrolyte excretion has not been measured. Ten normotensive blacks and 11 normotensive whites on a free diet were studied. Simultaneous 48-h urine and faecal collections were made. The results of the urinary measurements were in accordance with those of previous studies, in that 24-h urinary K excretion by blacks (38.2 ± 12.4 mmol) was significantly lower than that of whites (78.3 ± 16.6 mmol). As a result, there was a significantly higher urinary Na:K ratio in the black group. The mean 24-h faecal K excretion of the black group (15 ± 7.3 mmol) was not significantly lower, even when corrected for weight, than that of the white group (20.8 ± 10.8 mmol). It is concluded that the low urinary K excretion of South African urban blacks, compared with whites, is a reflection of a lower dietary K intake.

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