A single dose of oral nattokinase accelerates skin temperature recovery after cold water immersion: A double-blind, placebo-controlled crossover study

Nattokinase (NK) intake may improve blood flow; however, its effects on skin temperature, which is predominantly controlled by skin surface blood flow, are unknown. The purpose of this study was to determine the effects of a single dose of NK on changes in skin temperature after cold water immersion. A double-blinded, placebo-controlled, crossover intervention study was performed on nine healthy men. The participants were randomised to receive either a single dose of 2,000 fibrinolytic units (FU) of NK or a placebo with subsequent crossover. Two hours after supplementation, the participants immersed both hands in a water bath maintained at 10 °C for 1 min. Skin temperature, perceived coldness, cardiac output, and sympathetic nervous activity were measured before, during, and after water immersion. Two-way analysis of variance showed a significant effect of treatment interaction on the skin temperature of the middle finger, palm, and back of the right hand (p