Body fluid regulatory system consists of osmoregulatory and volume regulatory systems. Estrogen has an antidipsogenic effect, but estrogen’s action on osmoregulation is not fully elucidated. Body fluid volume regulation is achieved mainly by regulating sodium balance. Both estrogen and progesterone increases plasma volume; however, the mechanism for the expansion induced by estrogen and progesterone is likely different. Blood pooling and edema formation in the lower extremities are larger during luteal phase compared with other phases, suggesting that progesterone is possibly involved in the mechanism for these. However, effect of female reproductive steroids on body fluid and body fluid regulation remains unknown.

The effects of cardboard bed on initial stages of sleep under mild cold exposure were investigated. Twelve healthy male subjects slept from 13:15 to 15:15 on a floor (F) and a cardboard bed on the floor (B). Ambient temperature and relative humidity were maintained at 15℃ and 60%, respectively. Polysomnography recordings, skin temperature, microclimate, bed climate, and subjective sensations were obtained. No significant differences were observed in sleep parameters. Back skin temperature significantly increased in B than in the F. The bed climate temperature of the foot area in the later segment of sleep and back area were significantly increased in B compared with that in F. The subjective thermal sensation during sleep was significantly warmer, comfort sensation was significantly more comfort, and subjective stiffness of the bedding was significantly softer in B than it was in F. These results suggest that cardboard bed may increase subjective warm and comfort sensation by increasing back skin temperature and bed climate temperature of the back and foot area during sleep, and further improve stiffness sensation of the bedding.

This research identifies the dates that sports days in Japanese public elementary schools were held and evaluates the risk of heat disorders on those days. The dates of the sports days were determined from websites published by the schools, and data of wet-bulb globe temperature (WBGT) on sports days was obtained from the Ministry of the Environment. The risk of heat disorders on the sports days was assessed using the guidelines prescribed by the Japanese Sports Association. In all, 54.3% of elementary schools held their sports days during the spring, and the remaining 45.7% held theirs in autumn. On average, the first and last dates for sports days were May 16 and June 11 in the spring and September 11 and October 17 in the autumn. In Okinawa Prefecture, 99.0% of elementary schools held their sports days in hot weather, in which the risk of heat disorders was “Warning” and higher, but the number of heat disorder cases was as small as 5 cases. This might be explained by a heat acclimatization and appropriate measures for prevention of heat disorders. Determining the periods of higher risk of heat disorders for sports days based on daily maximum WBGTs will contribute to the prevention of heat disorders.