There is some evidence that young Japanese adults are sleeping longer. The health benefits from sleep are detailed in the linked paper: Sleep Health
A survey undertaken by Video Research Ltd. and Dentsu Inc., (1) of Japanese 20–34-year-olds, found that average sleep per day for men in 2019 of 7 hours 55 minutes was substantially higher than their 2009 survey (7 hours 11 minutes). Average sleep time also increased for women, to 7 hours 59 minutes in 2019 from 7 hours 19 minutes in 2009.
There has been a slow and steady trend to shorten Japan’s infamous long work hours. This allows both increased time for leisure, and for sleeping.
Perhaps the trend to longer sleep amongst young Japanese adults reflects the emergence of new knowledge-based industries and related flexible work practices, which those in their twenties and early thirties have been attracted to.
References:
- Japanese 20-somethings sleep eight hours a day – longer than 10 years ago, The Japan Times, 12 July 2020