Japanese in their 20s and early 30s are going to bed earlier and sleeping about eight hours a day, 40 to 50 minutes longer than the same demographic did 10 years ago, according to a recent survey.

The longer sleeping hours may be due to young people falling asleep while watching smartphones as they lie down, say Video Research Ltd. and Dentsu Inc., two companies that conducted and analyzed the survey last month.

The companies also point to a change in lifestyle in which young people prefer to stay home rather than working long hours and staying out late at night.