Roasted Barley Extract (Mugi-cha) Containing Cyclo(d‑Phe‑l‑Pro) Prevents Lowering of the Cutaneous Blood Flow and Skin Temperature under Air Conditioning: A Randomized, Double-Blind, Placebo-Controlled, Crossover Study

Roasted barley extract (RBE), also known as mugi-cha, is a well-known healthy non-caffeinated beverage, and its health functionality has been widely reported. Our previous clinical study showed that RBE affects the cutaneous blood flow and skin temperature after cold-water immersion and that cyclo­(d-Phe-l-Pro) is responsible for its effect. In this study, we investigated whether cyclo­(d-Phe-l-Pro)-containing RBE prevents the decrease in the cutaneous blood flow and skin temperature. Subjects remained in the air-conditioned room while ingesting RBE or a placebo. We measured the cutaneous blood flow and skin temperature. We evaluated the effect of RBE administration by two-way repeated measures analysis of variance. A total of 15 subjects were enrolled. The change in cutaneous blood flow in the RBE and placebo groups was −0.79 ± 0.38 and −2.03 ± 0.35 mL min^–1 100 g^–1, respectively (p value of 0.041). The change in the skin temperature in the RBE and placebo groups was −1.85 ± 0.35 and −3.02 ± 0.30 °C, respectively (p value of <0.001). We also did subclass analysis with cold-feeling subjects. For the seven subjects who had cold sensation, the change in the cutaneous blood flow in the RBE and placebo groups was −0.48 ± 0.58 and −2.56 ± 0.48 mL min^–1 100 g^–1, respectively (p value of 0.008). The change in the skin temperature in the RBE and placebo groups was −1.46 ± 0.74 and −2.89 ± 0.39 °C, respectively (p value of 0.009). Thus, RBE containing cyclo­(d-Phe-l-Pro) prevents the decrease in the cutaneous blood flow and skin temperature under air conditioning.