Moderating effects of smoking and drinking on the relationship between biological rhythm and psychological health and gender differences among adolescents

Three cities, including Shenzhen, Nanchang and Shenyang in China were chosen conveniently for this study. A cluster sampling method was conducted to select the study sample. First, we respectively extracted four large middle schools including junior and senior high schools and all participants were from grades 7 to 12, from each of the above three cities. Second, we randomly choose five classes for each grade in each chosen school and all students in selected classes were included in the survey, and about 2 700 students were chosen in each targeted region. Individuals with a family history of mental illness and being unwilling to participate in the survey were not included in the investigation. Finally, a total of 8,082 middle school students completed anonymous questionnaires in a classroom setting. Ninety-six incomplete questionnaires were excluded. The effective response rate was 98.8%. After excluding invalid questionnaires, including that the students were not at school on the investigation day, the students or their parents/caregivers were not reluctant to fill out the investigation questionnaire, and the students responded the questionnaires with an incomplete manner or dishonestly answered questionnaires or with logical errors, 7,986 adolescents, the range of the age from 8 to 23 years old, completed a standardized questionnaire finally, including 3,866 (48.4%) boys and 4,120 (51.6%) girls. In the study, only 0.1% of participants were less than 10-year-old who may have skipped a grade because of superior grades. Our study was approved and reviewed by the Ethics Committee of Anhui Medical University (Ethical No. 20,200,965). Our survey data were collected from October to December 2019, and all participants, parents and surveyed schools signed informed consent for inclusion before the administration of the survey.

Mental health was evaluated using the Chinese version of the fifteen-item Brief Instrument on Psychological Health of Youths (BIOPHY-15) [27]. The questionnaire was divided into the following three dimensions to assess mental health in the past month: emotional symptoms, behavior problems and social adaptation symptoms. Emotional symptoms were measured by 7 items, e.g., “You often lose interest in things” and “You often blame yourself”. Behavior problems in the past 30 days were assessed with 4-item short statements, e.g., “You often argue with other people” and “You often lose control of your temper”. The questionnaire comprises four items related to social adaptation symptoms, e.g., “You are often reluctant to ask for help when in trouble”. Each item had six possible answers: 1= “lasting ≥ 3 months”, 2= “lasting ≥ 2 months”, 3= “lasting ≥ 1 months”, 4= “lasting ≥ 2 week”, 5= “lasting ≥ 1 week”, 6= “none or lasting < 1 week.” The psychological symptoms were assessed by calculating the total score of all items; the total score ranges from 15 to 90; a lower score on the questionnaire implied more severe symptoms [27]. The skewness of BIOPHY-15 was − 1.093 ± 0.027, the kurtosis was 0.405 ± 0.055. The total Cronbach’s α coefficient of the psychological symptoms self-rating scale was 0.928, and the Cronbach’s α coefficients of the three dimensions (emotional symptoms, behavior problems and social adaptation symptoms) were 0.885, 0.815, and 0.777, respectively in the study.

Biological rhythm status was assessed using the Self-Rating of Biological Rhythm Disorder for Adolescents (SBRDA) [28]. The SBRDA consists of 29 items, reflecting four dimensions: sleep, digital media use, eating habits, and activities. Participants were required to think about their true biological rhythm status during the past 30 days. Sleep was evaluated by six items, e.g., “You get up an hour and a half later on weekends” and “You need an alarm clock or someone else to wake up in the morning”. Digital media use was measured by eight items, e.g., “You feel irritable or frustrated when you haven’t looked at your digital media for a long time”. Eating habits were assessed with eight-item, e.g., “You can’t keep eating regular amounts”. Activities were measured by seven-item, e.g., “You can’t keep pace with your family in your daily life”. Each item was rated on a five-point Likert scale, ranging from 1 = “completely untrue”, 2 = “basically untrue,” 3 = “somewhat true,” 4 = “basically true,” to 5 = “completely true.” The composite SBRDA score ranged from 29 to 145, corresponding to the levels from none to extreme; the higher the score on the questionnaire, the deeper the degree of biological rhythm disorder. The skewness of SBRDA was 0.351 ± 0.027, the kurtosis was 0.283 ± 0.055. The internal consistency of the SBRDA and each dimension, including sleep, digital, eating habits, and activities, in this study were 0.950, 0.834, 0.904, 0.893, and 0.817, respectively, which had also been confirmed by a sample containing approximately 10,000 adolescents [28].

Smoking among adolescents was evaluated based on the Youth Risk Behavior Survey System (YRBSS) [29]. The one question, “During the past month, how many days have you smoked cigarettes?” including four options (0 day, one to nine days, ten to nineteen days and twenty to thirty days), was used to measure the status of smoking.

Drinking was assessed based on the Youth Risk Behavior Survey System (YRBSS) [30]. “During the past a month, how many days did you drink a glass of wine (a glass of wine is equivalent to half a bottle of beer/a can of beer, a small cup of white wine, a glass of wine or rice wine)?” The question had four selection categories (0 day, one to nine days, ten to nineteen days, more than twenty days).

The validity of self-reported data on behaviors in adolescence that are relevant to smoking and drinking has been assessed [31, 32].

All statistical analyses in this study were conducted by SPSS version 23.0 (SPSS, Chicago, IL, USA). We assessed the sociodemographic characteristics of the sample using descriptive statistics. We conducted a chi-square test to compare the gender differences among different sociodemographic characteristics. Spearman correlation analysis was performed to test the correlations between smoking, drinking, biological rhythm, and mental health among Chinese adolescents and to examine gender differences. In SPSS PROCESS, the interacting effects (biological rhythm×smoking and biological rhythm×drinking) were calculated automatically on the software to explore whether smoking and drinking moderated the associations between biological rhythm and mental health among adolescents. and they also produced the proportions of the variances explained by the moderating effects of smoking and drinking (R² and F increased due to interaction). We adjusted the effects of sociodemographic characteristics (registered residence, only child status, and self-reported family economy) in the moderation models and compared the moderating effects between boys and girls, and the bootstrapping analysis with 5000 replicates was performed to determine the significance of the moderation effects. All P values were 2 tailed, and P < 0.05 implied that the moderating effects were statistically significant.