Association Between Physical Activity Frequency and Depression Severity Among Adults in the United States With Mild to Moderate Depression: A Cross-Sectional Analysis Using National Health and Nutrition Examination Survey (NHANES) Data

INTRODUCTION: Depression is a major contributor to global disease burden. While physical activity is often promoted as a protective factor, its independent association with depression severity remains unclear in population-based samples. This study examined the relationship between moderate-to-vigorous physical activity (MVPA) frequency and depression severity among U.S. adults with mild to moderate depressive symptoms. METHODS: We analyzed data from the 2015-2016 and 2017-2018 cycles of the National Health and Nutrition Examination Survey. Adults aged ≥18 years with Patient Health Questionnaire-9 (PHQ-9) scores between 5 and 14 were included. The outcome was total PHQ-9 score; the exposure was MVPA frequency, categorized as low (one to two days per week) and moderate/high (three or more days per week). Survey-weighted linear regression was used to adjust for demographic and clinical covariates. RESULTS: Among 1,865 participants (representing 41.2 million U.S. adults), MVPA three or more days per week was not significantly associated with depression severity (β = 0.141, p = 0.48). However, higher income-to-poverty ratio (β = -0.173, p < 0.01) and older age (β = -0.012, p < 0.01) were linked to lower PHQ-9 scores. Racial/ethnic minorities reported significantly higher depression scores than Mexican Americans. CONCLUSION: Physical activity frequency was not independently associated with depression severity. Socioeconomic and demographic factors were stronger predictors, highlighting the importance of addressing social determinants in depression interventions.