Effects of feet warming using bed socks on sleep quality and thermoregulatory responses in a cool environment

BACKGROUND: As a way of helping to sleep in winter, methods of warming the feet through footbaths or heating pads before bedtime are tried. In particular, bed socks are popular during winter sleeping in Korea, but scientific evidence about the physiological effects of bed socks on sleep quality is rarely reported. The purpose of this study was to evaluate the effect of feet warming using bed socks on sleep quality and thermoregulatory responses during sleep in a cool environment. METHODS: Six young males (22.7 ± 2.0 years in age, 175.6 ± 3.5 cm in height, and 73.1 ± 8.5 kg in body weight) participated in two experimental conditions (with and without feet warming) in a random order. The following variables on sleep quality using a wrist actigraphy were measured during a 7-h sleep at an air temperature of 23 °C with 50% RH: sleep-onset latency, sleep efficiency, total sleep time, number of awakenings, wake after sleep onset, average awakening length, movement index, and fragmentation index. Heart rate and rectal and skin temperatures were monitored during the 7-h sleep. Questionnaire on sleep quality was obtained after awakening in the morning. RESULTS: The results showed that sleep-onset latency was on average 7.5 min shorter, total sleep time was 32 min longer, the number of awakenings was 7.5 times smaller, and sleep efficiency was 7.6% higher for those wearing feet-warming bed socks during a 7-h sleep than control (no bed socks) (all P < 0.05). Also, their foot temperature was maintained on average 1.3 °C higher and the value in the distal-proximal skin temperature gradient was higher for those wearing feet warming bed socks when compared to the control condition (P < 0.05). However, there were no significant differences in heart rate, rectal and mean skin temperature, or in the questionnaire-based subjective evaluations between the two conditions. CONCLUSIONS: Feet warming using bed socks during sleep in a cool environment had positive effects on sleep quality by shortened sleep onset, lengthened sleep time, and lessened awakenings during sleep but had no significant influence on core body temperature. These results imply that sleep quality could be improved by manipulation of the foot temperature throughout sleeping.