Table 1.

Questions and answer options included in the survey

Variables	Questions	Answer options
Parental education level	What is the highest level of education your father/mother has obtained? (separately for father and mother）	Primary school or below, middle school, high school, college or university, master graduates or above, unknown.
Parental marital status	What is your parents current marital status?	Married, divorced, widowed, separated.
Academic performance	How would you describe your grades in your class?	Excellent, middle, poor.
Self-reported health	In general, how would you describe your health status?	Very good, good, fair, bad, very bad and unknown
Loneliness	During the past 12 months, did you ever feel lonely?	Never, occasionally, sometimes, often, always.
Physical activity	During the past 7 days, on how many days were you physically active for a total of at least 60 min per day?	None, 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days.
Breakfast	During the past 7 days, on how many days did you eat breakfast?	0 days, 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days.
Fruit	During the past 30 days, how many times per day did you usually eat fruit, such as apples, oranges, mangoes or papayas?	None, <1 time/day, 1 time/day, 2 times/day, 3 times/day, 4 times/day, ≥5 times/day.
Vegetable	During the past 30 days, how many times per day did you usually eat vegetables, such as cauliflower, cabbage?	None, <1 time/day, 1 time/day, 2 times/day, 3 times/day, 4 times/day, ≥5 times/day.
Carbonated beverages	During the past 30 days, how many times per day did you usually drink carbonated soft drinks, such as Coca-Cola, Pepsi or Sprite? (Do not include diet soft drinks.)	None, 1-3 times/week, 4-6 times/week, 1 time/day, 2 times/day, 3 times/day, ≥4 times/day.