Trends in blood pressure and urinary sodium and potassium excretion in Japan: reinvestigation in the 8th year after the Intersalt Study

Abstract

Using the identical protocol of an Intersalt Study previously conducted, we undertook a new study (Intersalt-2) 8 years later. We measured changes in various factors affecting blood pressure (BP) including urinary sodium and potassium excretion in three districts of Japan: Osaka, Tochigi, and Toyama. Also we evaluated the trends in the relationships of those factors to BP.

The Intersalt Study revealed that the average sodium excretion of all three study centres was high (particularly in Toyama) while potassium excretion was relatively low. The sodium/potassium ratio was therefore relatively high. The body mass index (BMI) was favourable, but the prevalence of heavy alcohol drinkers was high.

Comparing the first to the second study reveals a decrease in sodium excretion in Toyama, although that area still had the highest value of the three study centres. The average potassium excretion increased only in Osaka. Sodium/potassium ratio decreased in all centres. BMI and the prevalence of heavy drinkers among the subjects of both studies were nearly the same. The trend of the relationship of sodium to BP in Osaka changed from negative to positive. In Toyama, it changed from positive to negative. It is thought that this negative relationship might occur in conjunction with a reduction in salt consumption in a population.

In conclusion this study reveals that average sodium consumption in Japan remains high while potassium consumption is still low. As a factor in the prevention of hypertension, further efforts to reduce salt consumption and increase potassium intake are still needed.