Urinary sodium and potassium excretion, body mass index, alcohol intake and blood pressure in three Japanese populations.

Standardised data on blood pressure, 24 hour urinary electrolyte excretion and other lifestyle factors were obtained in three Japanese populations as part of the INTERSALT study. Urinary sodium excretion and sodium/potassium ratio were significantly (P less than 0.01) higher in Toyama (a semi-rural area in central Japan) than in Tochigi (a rural area 100 km north of Tokyo) and Osaka. There were also significant (P less than 0.01) differences between the centres in diastolic blood pressure (highest in Toyama), although systolic pressure was similar in all three centres. Average potassium excretion was low (46 mmol/day), and the prevalence of both heavy alcohol drinking (greater than or equal to 300 ml/week) and smoking was high in men (33% and 61% respectively); compared with other countries, there were favourable levels of body mass index (mean 22.4 kg/m2). Despite a recent decline in sodium consumption in Japan, which has been accompanied by a fall in blood pressure levels, in the prevalence of hypertension and also in stroke mortality, average sodium excretion in the three centres was high compared to other countries (187 mmol/day). Applying overall INTERSALT regression coefficients to the Japanese data, suggested that further falls in sodium intake together with a modest increase in potassium intake and a reduction (in men) in the prevalence of heavy alcohol drinking could have an important impact on average blood pressures and the prevalence of hypertension. It can be expected that these nonpharmacological approaches to improved blood pressure levels will be accompanied by continued reductions in mortality from stroke.