Blood-pressure and its correlates in urban and tribal Africa.

Blood-pressure and associated factors were compared in tribal and urban Xhosa people of Southern Africa. In the urban group blood-pressures were high and rose significantly with age whereas in the tribal group they were low and rose little with age. Indices of obesity including weight, skin-fold thickness, and ponderal index were significantly greater in urban dwellers and correlated strongly with arterial pressure. Dietary sodium and urine-sodium/creatinine ratio were significantly higher in the urban people, but there was no within-population relationship between either dietary sodium or urine-sodium/creatinine ratio and blood-pressure. Plasma-noradrenaline, an index of sympathetic activity, was similar in both populations, as was plasma-renin activity. Low plasma-renin was common and may be genetically determined. Diet and obesity may contribute to the rise in arterial pressure that is a consequence of urbanisation.