Changes in health behaviors and risk of depression after breast cancer diagnosis and treatment: a nationwide cohort study

Purpose: Protective lifestyle behaviors could potentially mitigate the risk of depression in breast cancer survivors. This study examined the association between changes in key health behaviors and depression risk after breast cancer diagnosis and treatment. Methods: This nationwide cohort study assessed 30,523 breast cancer survivors without a prior history of depression, focusing on changes in weight, smoking habits, alcohol consumption, and physical activity from pre- to post-cancer diagnosis. The primary outcome was incident depression, with adjusted hazard ratios and confidence intervals calculated to consider potential confounders. Results: During an average follow-up of 5.3 years (160,755 person-years), lifestyle changes post-diagnosis included decreases in smoking (2.8% to 0.9%) and alcohol consumption (24.9% to 7.5%) and an increase in physical activity (18.9% to 32.1%). Substantial weight gain (> 10%) was associated with a 27% elevated risk of depression compared to those who maintained weight. Both continuation and cessation of smoking were associated with increased depression risk compared to sustained non-smokers. Changes in alcohol consumption, either initiation or cessation, were associated with increased depression risk compared to sustained non-drinkers. Conversely, breast cancer survivors who became inactive post-diagnosis had a reduced risk of depression compared to those who remained inactive. Our exploratory analysis showed that regular physical activity prior to diagnosis was associated with a 7% lower risk of depression compared to inactivity. Conclusion: We observed that post-diagnosis weight gain exceeding 10%, sustaining or quitting smoking, starting or stopping alcohol consumption, and pre-diagnosis physical inactivity were all associated with an increased risk of depression in breast cancer survivors. Healthcare providers should support healthy behaviors to mitigate depression risk after breast cancer diagnosis and treatment.