This study describes the effect of bovine alpha-S1 casein tryptic hydrolysate (CTH) in a representative sample of day-time workers from the general population of Japan with the occurrence of insomnia during the preceding six months. To investigate this issue, 32 subjects, aged between 25 and 40 years, were examined for the subjective sleep quality using the Japanese Pittsburg Sleep Quality Index (PSQI-J). CTH significantly improves the PSQI total score of the treated subjects. It particularly improves the sleep quality after two weeks of treatment, decreases the sleep latency and the daytime dysfunction after four weeks of treatment. Given the antistress properties of CTH, it seems possible to relate the detected improvement of sleep aspects to a reduction of stress following its’ chronic administration. In conclusion, being given its beneficial effects and its absence of negative side effects, it would be advantageous to use the CTH to improve chronic insomnia in the Japanese general population. However, further studies will be necessary in order to clarify the essential aspect of CTH properties in the sleep problems. <\/p>\n\n\n\n