Characteristics of nursing students and lifestyle/social activities

Students were required to answer questions on age, sex, grade, starting and closing time of class, whether they were living alone or not, commute time, exercise habits per week (≥ 4 days /2–3 days/ ≤ 1 day/ none), duration of habitual exercise, start time of exercise, engagement in part-time job (yes /no), part-time job after 10 p.m., starting and closing time of part-time job, participation in a club activity (yes/no), and starting and closing time of club activity. Frequency of exercise habit was converted into a binary outcome (0: none, 1: ≥ 4 days /2–3 days/ ≤ 1 day) for analysis.

Data on sleep pattern included information on sleep duration, bedtime, awakening time on weekdays and on weekends. The Japanese version of Epworth Sleepiness Scale (ESS) (Cronbach’s α = 0.88) [35–37] was used to assess the level of daytime sleepiness. The total sum score ranges from 0 to 24, and ≥ 11 is regarded as having excessive daytime sleepiness. Sleep quality was assessed with the Japanese version of Athens Insomnia Scale (AIS) (Cronbach’s α = 0.89) [38, 39], which indicates possible insomnia when one has a score above five out of the total score. In order to assess sleep-related symptoms, the self-report questionnaire included questions on difficulty initiating sleep, difficulty maintaining sleep, early morning awakening, and/or difficulty awakening.

Information regarding eating patterns included meal time, duration of meal, skipping meals, and frequency of skipping meals at breakfast, lunch, and dinner. In addition, students were required to answer questions on body weight gain after entering the university. Body mass index (BMI) was calculated by self-reported height and weight.