Scientists from Anhui Medical University (China), led by Wanyu Che, Ziyan Ruan and Xiaoyan Wu, traced how adolescents' everyday habits are linked to their mental health. The work was published in the journal BMC Psychiatry.
The study involved 6,656 schoolchildren from eight regions of China - from first- and second-tier cities, including urban and rural areas. The average age was about 14, with roughly equal numbers of middle and high school students. The survey was conducted twice: in autumn 2021 and a year later. The schoolchildren filled out electronic questionnaires on smartphones during lessons.
The scientists were interested in 15 unhealthy habits: smoking, alcohol, lack of physical activity, too-short sleep, late bedtime, excessive screen time on weekdays and weekends, as well as dietary features - few fruits and vegetables, frequent fast food, skipping breakfast, sugary drinks. Separately, they asked about thoughts, plans and actions related to suicide. Anxiety and depression were assessed using standard self-report scales.
A year later, 13.6% of participants simultaneously had symptoms of anxiety and depression - so-called comorbidity, that is, the combination of two conditions in one person. This occurred more often in girls, as well as in adolescents with a high academic workload, from less well-off families, and in those who had two friends or fewer.
The researchers then used statistical models to divide the schoolchildren into groups by their set of habits. In the low-risk group (24% of the sample) there were almost no bad habits. About 40% were adolescents with poor nutrition: they often skipped breakfast, ate fast food and had few vegetables and fruits. Another 22% fell into the group of those who were physically inactive and spent a lot of time in front of screens. Almost 14% were in the group with multiple bad habits - they had most of the 15 items, including suicidal thoughts and actions.
More than half of the participants had four to six bad habits, and about a quarter had seven or more. After adjusting for family income, number of friends, academic workload and family history of depression, it turned out that adolescents in the physically inactive and multiple-habits groups had a noticeably higher risk of having anxiety and depression at the same time than the low-risk group. Those who had seven or more bad habits had chances almost three times higher than those who had three or fewer.
To check whether the suicide questions were distorting the results, the scientists repeated the analysis without three such items - using only the 12 habits related to nutrition, sleep and movement. The conclusions did not change: a clustering of bad habits still predicted an increased risk. This is a correlation - a statistical association that by itself does not prove causation.
The authors suggest that such combinations of habits may be a common basis for vulnerability to internal problems, rather than a specific trigger for anxiety or depression. The study is observational, so it cannot prove that habits directly cause disorders: unaccounted factors, such as childhood trauma or neighborhood conditions, may influence both lifestyle and mental health. In addition, the data are based on self-reports, and the sample included only schoolchildren - those who dropped out of school may have different risks.