Salt intake in an urban, developing South African community

Present guidelines for the diagnosis and management of hypertension indicate that a reduction in sodium (Na(+)) intake levels and an increase in potassium (K(+)) intake levels are critical components of blood pressure (BP) control. Whether this is being successfully implemented in urban, developing communities in South Africa is uncertain.

The first was to assess how mean 24-hour urinary Na(+) and K(+) excretion rates, used as an index of salt intake, compared against recommended daily allowances (RDA) for Na(+) and K(+) intake in an urban, developing South African community. The second was to determine the relationship between hypertension awareness and treatment, and 24- hour urinary Na(+) and K(+)excretion rates in this community.

Four hundred and thirty-eight subjects living in metropolitan areas of Johannesburg, of whom 291 had complete 24-hour urine collections and BP measurements, obtained on three separate occasions, were randomly recruited. Thirty-one per cent of the sample of 291 subjects were hypertensive (either receiving therapy or with an average BP measured on three separate occasions > or =140/90 mmHg). Sixty-seven per cent of hypertensives were aware of their hypertension and were being treated for it. On average, 82% of subjects had 24-hour Na+ excretion values above the RDA for Na(+) intake of 65 mmol/day. All subjects had 24- hour K(+) excretion rates below the RDA for K(+) intake (120 mmol/day). The mean value for 24-hour urinary Na(+) and K(+) excretion rates (mmol/24 hours) in patients who were aware of their hypertension and receiving treatment for it (n = 61; Na(+) = 112 +/- 54, K(+) = 32 +/- 16) was similar to that of patients who were unaware of their hypertension (n = 30; Na(+) = 102 +/- 49, K(+) = 28 +/- 13), or to normotensives (n = 200; Na(+) = 117 +/- 56, K(+) = 33 +/- 17). Hypertension awareness and treatment were not associated with electrolyte excretion rates either when considered alone or after adjusting for age, gender, body mass index, alcohol and tobacco intake, the presence of diabetes mellitus and the type of antihypertensive therapy (multivariate regression analysis). Moreover, the proportion of patients who were aware of their hypertension, were receiving treatment for it, and who had 24-hour Na(+) excretion values above the RDA for Na(+) intake (80%) was similar to the proportion noted in those who were unaware of their hypertension (73%), and to normotensives (84%).

The lack of relationship between either hypertension awareness and treatment, and Na(+) and K(+) intake levels suggests that current recommendations for a reduced Na(+) and increased K(+) intake in hypertensives do not translate into clinical practice in urban, developing communities of South Africa.