Social Jet Lag in Japan

I happened upon a Japan Times article from September 2nd 2025 that mentioned a sleep research report from University of Tsukuba in conjunction with the Pokemon Sleep app. It reported that 18% of the 80,000 app users indicated "social jet lag". Moreover, the report estimated that social jet lag cost Japan roughly one trillion yen a year. 

The phrase “social jetlag” was introduced to describe a chronic form of circadian disruption that resembles travel jet lag, but is caused by lifestyle patterns rather than time‑zone changes. According to Copilot, the term was coined in 2006 by German Chronobiologist Till Roenneberg, referring to the mismatch between your biological clock and your socially required schedule. A prime example is waking early on weekdays but sleeping in on weekends.

I was surprised that only 18% of app users indicated "social jet lag". Long working hours and early school schedules in Japan clash with natural sleep rhythms. But it is calculated by comparing the midpoint of sleep on workdays versus free days. Perhaps the low percentage can be explained by the fact that many people in Japan get too little sleep every day of the week, even on their free days!