【Background】
In a previous study, the authors confirmed that the cyclic dipeptide cyclo (D-Phe-L-Pro), a bitter component of roasted barley extract (Mugicha), has vasodilatory effects through the release of nitric oxide in the vascular endothelium in animal studies. That roasted barley extract significantly promotes the recovery of skin temperature in the palms of the hands after cold water stress in human study on healthy women *1. In this study, we conducted a placebo-controlled, randomized, double-blind study to examine the effect of drinking roasted barley tea containing cyclo(D-Phe-L-Pro) on skin temperature regulation in an air-conditioned room.
【Methods】
Eighteen healthy adult males and females were randomly divided into two groups: one group drank roasted barley tea, and the other group drank placebo (0 μg cyclo(D-Phe-L-Pro), 0 kcal). 250 mL of roasted barley tea containing 258 μg cyclo(D-Phe-L-Pro) (3 kcal) and 250 mL of placebo with food coloring and food additives to mimic the appearance and taste of roasted barley tea were used as test beverages. The study was conducted in a crossover design.
The subjects wore thin clothing such as cotton T-shirts and waited in a room with a room temperature of 28.0±0.5°C for 2 hours, then sat on a chair in an air-conditioned room with a room temperature of 25.5±0.5°C and humidity of 52.5±7.5% for 30 minutes (acclimatization to room temperature). Afterward, they took off their socks and drank barley tea or a placebo drink. The temperature of the back of the left foot was measured at 5-minute intervals, starting at 0 minutes just before drinking and continuing until 100 minutes later. Infrared thermography was used to measure the skin temperature.
【Results】
All participants performed the test, but 6 participants were excluded from the analysis due to insufficient data, and the data of 12 participants were analyzed. Skin temperature was significantly higher after drinking barley tea at all time points except 35 minutes after drinking. In the analysis of males (n=4) and females (n=8), skin temperature was significantly higher in males at 10, 20, 35, 50, and 55 minutes after drinking, and in females at 10, 45, 50, and 55 minutes after drinking.
【Discussion and conclusion】
The skin temperature after consumption of the placebo beverage decreased after the start of the experiment, suggesting that the temperature of the room where the test was conducted was moderately cold. The decrease in skin temperature after consumption of the barley tea beverage was significantly lower than that after consumption of the placebo beverage. The effect of barley tea on reducing the decrease in skin temperature is due to vasodilation caused by cyclo(D-Phe-L-Pro).
In the authors' previous study *1, all human test subjects were female. However, in this study, the authors confirmed that the decrease in skin temperature was suppressed in males. We conclude that the consumption of barley tea prevents the reduction in skin temperature under cold conditions.
【Research institution】
Kirin Co. Ltd.
*1 J Agric Food Chem 66, 5, 1251-7, 2018
Roasted Barley Extract (Mugicha) Containing Cyclo(d-Phe-l-Pro) Prevents a Decrease in Skin Temperature in Cold Conditions: A Randomized, Double-Blind, Placebo-Controlled, Crossover Study
J Nutr Sci Vitaminol 65, 90–3, 2019
