Effects of aging on morningness-eveningness and sleep habits in Korean and Japanese workers.

The Morningness-Eveningness Questionnaire and Life Habits Inventory were given to Korean and Japanese workers. The distributions of scores on the questionnaire for these two groups were normal and its mean slightly moved to the Morning type with aging. It is noteworthy, however, that the mean scores of Korean workers was lower than those of the Japanese workers. The self-reported waking times and bedtimes for the two groups gradually became earlier with aging. From these results it could be said that aging was an factor that led to the difference of circadian phase.