Ethnic differences in salt sensitivity: genetic or environmental factors?

1. The CARDIAC study, a world-wide cross-sectional epidemiological study on the relationship between alimentary factors and cardiovascular diseases, provided the initial evidence of ethnic differences in salt sensitivity; this was because despite much less urinary sodium excretion in Tanzania than in Brazil and the Japanese, the prevalence of hypertension was relatively higher in Tanzania than in the latter two populations. 2. To investigate this difference in salt sensitivity, a standardized clinical experiment was carried out: six to 13 male volunteers were placed on 2500 kcal basal diets containing 3 g salt/day. Eighteen grams of salt were added daily from the sixth to the 11th day in Tanzania and Brazil, while 22 g of salt were added in Japan. 3. Salt loading induced a significant rise in systolic blood pressure (SBP) on the second day of the high salt period (HSP) in Japan, the second and third day of HSP in Brazil, and all days of HSP in Tanzania. 4. Salt sensitivity was seen in 16.7% of the participants in Japan, 36.4% in Brazil and 46.2% in Tanzania. Further analysis of the effect of salt on blood pressure (BP) was carried out using the data from the CARDIAC study by multiple regression analysis. A within-centre comparison of fatty acid was also made. 5. The regression analysis revealed that the relationship of salt and blood pressure is more positively tight in Tanzania than Brazil and Japan after controlling for other confounding variables. Fatty acids in serum phospholipids contain significantly more palmitic acid and showed lower P/S ratios than those from Brazil and Japan.