Clustering of unhealthy habits linked to higher depression risk, study suggests

New research has revealed that individuals accumulating several unhealthy lifestyle habits—such as poor diet, lack of exercise, and suboptimal sleep—are significantly more likely to experience depression, according to a new study published in the Journal of Affective Disorders.

Depression affects millions worldwide and is influenced by many factors, including genetics, environment, and behavior. While previous research has shown that individual habits like smoking or poor sleep can raise the risk of depression, this new study takes a broader view by examining how these behaviors interact as a group.

Led by Qian Tian, researchers from Fudan University and Shanghai University in China wanted to understand whether a combined measure of unhealthy lifestyle behaviors (ULB) could help predict depression risk more effectively than looking at each habit in isolation. They developed a scoring system based on five key behaviors: poor diet, physical inactivity, irregular sleep, smoking, and excessive alcohol use.

Data was extracted from the National Health and Nutrition Examination Survey, which included 21,854 participants from the USA between 1999 and 2018 (average age of 46 years, 52% males). The team then analyzed how ULB scores related to depression. Depression was measured using a standard questionnaire called the Patient Health Questionnaire-9, with scores of 10 or higher indicating likely depression.

The research group discovered that 7% of participants met criteria for depression and that depression was more common in women. Individuals with higher ULB scores were much more likely to be depressed. In fact, those in the highest quartile of unhealthy behaviors had nearly twice the risk of depression compared to those with the healthiest lifestyles. The relationship wasn’t just linear – depression increased in severity as the unhealthy behaviors accumulated. This pattern held true across all age groups, genders, and health conditions.

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“The interaction between unhealthy lifestyle behaviors (ULB) and depression may affect emotions and behaviors through various mechanisms. Firstly, unhealthy lifestyle behaviors often coexist with other chronic diseases such as hypertension. … Secondly, unhealthy diets and lifestyle habits can alter brain structure and function. … Finally, unhealthy lifestyle behaviors often accompany social isolation and low self-esteem, leading to negative emotions and psychological stress, thus increasing the risk of depressive symptoms,” Tian and colleagues explained.

The researchers believe this scoring system could be used in routine health screenings to identify people at risk of depression early. By assessing lifestyle habits alongside mental health questionnaires, doctors and social workers could offer more targeted support and interventions.

However, the study does have limitations. As it was a cross-sectional analysis (a snapshot in time), it cannot prove that unhealthy habits cause depression—only that the two are strongly linked. It’s also possible that depression leads to a less healthy lifestyle. Additionally, the data relied on self-reported habits, which can introduce bias.

The study, “The relationship between unhealthy lifestyle behaviors and depression: Evidence from NHANES,” was authored by Qian Tian, Jiahui Guo, Jingyun Ding, and Yan Zhu.