Review of the health benefits of habitual consumption of miso soup: focus on the effects on sympathetic nerve activity, blood pressure, and heart rate

Abstract

High salt intake increases blood pressure, and dietary salt intake has been clearly demonstrated to be associated with hypertension incidence. Japanese people consume higher amounts of salt than Westerners. It has been reported that miso soup was one of the major sources of daily salt intake in Japanese people. Adding salt is indispensable to make miso, and therefore, in some cases, refraining from miso soup is recommended to reduce dietary salt intake. However, recent studies using salt-sensitive hypertensive models have revealed that miso lessens the effects of salt on blood pressure. In other word, the intake of miso dose not increase the blood pressure compared to the equivalent intake of salt. In addition, many clinical observational studies have demonstrated the absence of a relationship between the frequency of miso soup intake and blood pressure levels or hypertension incidence. The mechanism of this phenomenon seen in the subjects with miso soup intake has not been fully elucidated yet. However, in basic studies, it was found that the ingredients of miso attenuate sympathetic nerve activity, resulting in lowered blood pressure and heart rate. Therefore, this review focused on the differences between the effects of miso intake and those of the equivalent salt intake on sympathetic nerve activity, blood pressure, and heart rate.

Keywords: Blood pressure; Heart rate; Hypertension; Miso; Sympathetic nerve activity.

Fig. 1

a SNA evaluated on the basis of uNE excretion in each group. *p < 0.05, **p < 0.01 Sham versus CPO, n = 8 for each. Open bar graphs indicate Sham; square-block bar graph indicates CPO. b The ratio of uNE/uNa excretion, as a marker of SNA in response to salt intake. ***p < 0.001 Sham versus CPO, n = 24 for each. Open bar graphs indicate Sham; square-block bar graph indicates CPO. SNA, sympathetic nerve activity; Sham, sham-operated control mice; CPO, chronic pressure overload mice; uNE, 24-h urinary norepinephrine; uNa, 24-h urinary sodium

Fig. 2

a SNA evaluated on the basis of uNE excretion in each group. ^##p = 0.001, CPO-H versus CPO-miso, n = 8 for each. Open bar graphs indicate CPO-miso; square-block bar graph indicates CPO-H. b Na intake in terms of uNa excretion in each group. ^##p = 0.001, CPO-H versus CPO-miso, n = 8 for each. Open bar graphs indicate CPO-miso; square-block bar graph indicates CPO-H. c The ratio of uNE/uNa excretion, as a marker of SNA in response to salt intake. ^###p < 0.001, CPO-H versus CPO-miso, n = 8 for each. Open bar graphs indicate CPO-miso; square-block bar graph indicates CPO-H. SNA, sympathetic nerve activity; CPO-H, chronic pressure overload mice with high salt water; CPO-miso, chronic pressure overload mice with miso soup; uNE, 24-h urinary norepinephrine; uNa, 24-h urinary sodium

Fig. 3

Blood pressure levels and heart rates in each group. G1, Group 1 (< 1 bowl of miso soup/week); G2, Group 2 (< 4 bowls of miso soup/week); G3, Group 3 (< 7 bowls of miso soup/week); G4, Group 4 (≥ 7 bowls of miso soup/week). *p < 0.05 versus G1

Fig. 4

a Systolic blood pressure in normal mice after IP injection of high-sodium saline or miso supernatant. n = 5 for each. *p < 0.05 high-sodium saline versus miso supernatant. b LF/HF ratio (left) and heart rate (right) in normal mice evaluated via ECG. The LF/HF ratio before the injection was assigned a value of 1.0. n = 9 for each. *p < 0.05, **p < 0.01 high-sodium saline versus miso supernatant. IP, intraperitoneal; LF, low frequency power of heart rate variability; HF, high frequency power of heart rate variability

Fig. 5

LF/HF ratio in CPO-mice evaluated via ECG. The LF/HF ratio before the injection was assigned a value of 1.0. n = 5 for each. **p < 0.01 high-sodium saline versus miso supernatant. LF, low frequency power of heart rate variability; HF, high frequency power of heart rate variability

Fig. 6

Changes in mean blood pressure (left) and heart rate (right) after high-sodium saline ICV infusion. n = 5 for each. *p < 0.05, **p < 0.01 high-sodium saline versus miso supernatant. ICV, intra-cerebroventricular