Salt intake and blood pressure in rural and metropolitan Mexico

A selected group of 155 Mexican adults aged 20-64 years were studied to investigate the role of sodium (Na) intake in explaining blood pressure (BP) differences in a rural town and urban Mexico City. The subjects had their BP, height, weight and skinfolds measured and they collected 3 continuous 24 h urines. Adjusted for age differences, average BPs were significantly higher (p < .05) for the urban (112.7 systolic: 73.6 diastolic mmHg) than for the rural group (108.4 systolic: 70.8 diastolic mmHg). They were also higher for men (111.8 systolic: 74.3 diastolic mmHg) than for women (109.6 systolic: 70.2 diastolic mmHg), the diastolic BP difference being significant (p < 0.05). The average daily Na excretion was also higher in the urban (122.2 mmol/day) than in the rural community (98.0 mmol/day) (p < 0.01). Potassium excretion rates showed similar differences. The differences in sodium excretion and blood pressure among communities were particularly marked in those over 30 years of age. The means for the four community-sex groups had the same rank order for both BP and Na. However, although some large surveys have suggested that half the observed differences in BP might be explained by different Na intakes, in this study the relationship between Na excretion and BP did not achieve statistical significance. Differences in the body mass index (BMI) accounted for 41% of the observed variance in BP.