The role of dietary inflammatory index and physical activity in depressive symptoms: Results from NHANES 2007-2016

Background: Depression is a major public health problem. This study was aimed to analyze the relationship between Dietary Inflammatory Index (DII), physical activity, and depressive symptoms, and to explore the effect of different lifestyles on depressive symptoms by combining DII and physical activity to form four lifestyle groups. Methods: This study analyzed data from the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2016. A total of 21,785 subjects were involved. Depressive symptoms and dietary inflammation were measured by the Patient Health Questionnaire (PHQ-9) and Energy-adjusted Dietary Inflammatory Index, respectively. The participants were divided subgroups by different physical activity combined pro-inflammatory or anti-inflammatory diet groups.Results: Both pro-inflammatory diet and inactivity were positively associated with depressive symptoms. Compared with the anti-inflammatory diet & active group, the risk of depressive symptoms was 2.061 times higher in the pro-inflammatory diet & inactive group, 1.351 times higher in the pro-inflammatory diet & active group, and 1.603 times higher in the anti-inflammatory diet & inactive group. Physical inactivity was associated with a higher risk of depressive symptoms than a pro-inflammatory diet. Females and the 20-39 age group showed a strong association between lifestyles and depressive symptoms. Limitations: Because of the cross-sectional study, no causal conclusions could be drawn. Moreover, PHQ-9 is a relatively basic method of identifying depressive symptoms, more and further research is needed.Conclusions: Both a pro-inflammatory diet and physical inactivity were associated with higher risk of depressive symptoms, especially for young and female population.