Late chronotype and daytime sleepiness are associated with unhealthy life habits, including consumption of alcohol and caffeinated beverages and smoking, in Korean high school students, according to study results presented at World Sleep 2019, held September 20 to 25, in Vancouver, Canada.

The goal of the current study was to focus on Korean high school students and explore the association between unhealthy life habits and chronotype. The cross-sectional study included adolescents aged 15 to 19 years, from 75 middle and 75 high schools to represent adolescents nationwide from 15 administrative districts in South Korea.

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Morningness Eveningness Scale for Children (score range 10-43), Epworth Sleepiness Scale (ESS), and Internet Addiction Proneness Scale for Youth were used for assessment of chronotype, daytime sleepiness, and internet addiction.

Of 12,672 high school students recruited for the study, 8565 individuals (47.9% females, mean age 16.8 years±0.85) met inclusion criteria. The researchers used a questionnaire to collect data on sleep habits, including sleep patterns on weekdays and weekends, and consumption of coffee, alcohol, and cigarette.

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Regular coffee consumption was reported by 3675 participants (42.9%), regular alcohol consumption was reported by 732 participants (8.5%), and cigarette smoking was reported by 576 participants (6.7%).

The mean Morningness Eveningness Scale for Children score for all participants was 24.51±4.36; researchers categorized participants into 3 groups according to score tertiles: 1st (11-22), 2nd (23-26), and 3rd (27-41).

A significant positive association was found between coffee consumption and 1st tertile of scores (odds ratio [OR] 1.29; 95% CI, 1.14-1.46), age (OR 1.22; 95% CI, 1.16-1.29), female gender (OR 1.10; 95% CI, 1.01-1.21), ESS (OR 1.04; 95% CI, 1.03-1.05), and attending private lessons. Conversely, weekday sleep duration was negatively associated with coffee consumption (OR 0.85; 95% CI, 0.81-0.89).

In regards to alcohol consumption, there was a significant positive association with 1st tertile of scores (OR 1.35; 95% CI, 1.09-1.66), weekday sleep duration (OR 1.18; 95% CI, 1.09-1.27), ESS (OR 1.06; 95% CI, 1.04-1.09), and a negative association with female gender (OR 0.41; 95% CI, 0.34-0.49) and attending private lessons.

Smoking was also significantly associated with 1st tertile scores (OR 2.13; 95% CI, 1.67-2.72), age (OR 1.38; 95% CI, 1.24-1.54), weekday sleep duration (OR 1.18; 95% CI, 1.09-1.28), and ESS (OR 1.06; 95% CI, 1.03-1.08). There was a negative association between smoking and female gender (OR 0.21; 95% CI, 0.17-0.27).

“Late chronotype was independently associated with higher probability of coffee, alcohol, or cigarette consumption,” concluded the researchers. They added that “daytime sleepiness was also positively associated with these consumptions in Korean high school students.”


Kim D, Kim JH, Hwangbo Y, et al. Late chronotype and daytime sleepiness are associated with consumption of coffee, alcohol, and smoking in Korean high school students. Abstract presented at World Sleep 2019; September 20-25, 2019; Vancouver, Canada.