Traditional Japanese food, such as miso, contains 10-15 ％ （w/w） salt. However, recent studies on human subjects have demonstrated that long-term miso intake does not affect day-time blood pressure （BP） in subjects with high normal to stage I hypertension. Moreover, miso intake significantly decreases night-time BP in subjects with stage I hypertension. These studies clearly indicate that miso intake attenuates hypertensive response to salt intake. Experimental animal studies revealed that long-term miso intake significantly decreases salt-induced hypertension in Dahl salt-sensitive （Dahl S） rats. The attenuation of salt sensitivity is caused by enhanced Na excretion in the kidney through increased dopaminergic systems and is probably due to reduced body fluid volume. Miso is also found to contain substances that directly dilate arterial vessels, probably through an increase in nitric oxide formation. The natriuretic effects and possible nitric oxide formation may be mediated by a decrease in oxygen stress. These rats studies clearly suggest that BP increase in response to salt intake is subject to whatever food with which the salt is consumed. The relationship of salt to health risk should be assessed by measuring the net salt intake rather than salt intake only. This provides new helpful evidence to determine the optimum daily salt intake in humans, a theory that has not reached any consensus so far.
