Diet and blood pressure in South Africa: Intake of foods containing sodium, potassium, calcium, and magnesium in three ethnic groups

Abstract

Objectives: We investigated whether habitual intakes of sodium (Na), potassium, magnesium, and calcium differ across South African ethnic groups, assessed the proportion of Na intake, which is discretionary, and identified which food sources were the major contributors to Na intake.

Methods: This was a cross-sectional study of 325 black, white, and mixed ancestry hypertensive and normotensive subjects. Three repeated 24-h urine samples were collected for assessment of urinary Na, and three corresponding 24-h dietary recalls were administered by trained fieldworkers. Blood pressure and weight were measured at each visit. Secondary analyses were performed on existing dietary databases obtained from four regional surveys undertaken in South African adults.

Results: Mean urinary Na excretion values equated to daily salt (NaCl) intakes of 7.8, 8.5, and 9.5 g in black, mixed ancestry, and white subjects, respectively (P < 0.05). Between 33% and 46% of total Na intake was discretionary, and, of the non-discretionary sources, bread was the single greatest contributor to Na intake in all groups. Ethnic differences in calcium intake were evident, with black subjects having particularly low intakes. Urban versus rural differences existed with respect to sources of dietary Na, with greater than 70% of total non-discretionary Na being provided by bread and cereals in rural black South Africans compared with 49% to 54% in urban dwellers.

Conclusion: White South Africans have higher habitual intakes of Na, but also higher calcium intakes, than their black and mixed ancestry counterparts. All ethnic groups had Na intakes in excess of 6 g/d of salt, whereas potassium intakes in all groups were below the recommended level of 90 mM/d. Dietary differences may contribute to ethnically related differences in blood pressure.