Lifestyle factors and BMI attenuate relationships between biomarkers of inflammation and depressive symptoms and well-being: A cross-sectional study

Background: Mental disorders are a growing public health concern and evidence has linked chronic low-grade inflammation with depression and well-being. Research also suggests that certain modifiable lifestyle factors such as smoking, alcohol use, physical activity, diet quality and BMI are related to psychological health. These may modulate the relationship between low-grade inflammation and mental health conditions. In this study we examined inflammatory biomarker associations with two psychological health scores and investigated whether relationships are influenced by lifestyle factors and BMI. Methods: This was a cross-sectional study of 1824 middle-to older-aged men and women randomly selected from a large primary care centre. Depressive symptoms and well-being were assessed using the 20-item Centre for Epidemiologic Studies Depression (CES-D) Scale and the World Health Organization-Five (WHO-5) Well-Being Index. Linear regression analyses were performed to examine depression and well-being score relationships with six inflammatory biomarkers, and a composite inflammatory biomarker score, adjusting for demographic characteristics, health conditions, lifestyle factors and BMI. Results: Depression and well-being score associations with complement component 3 (CES-D only) c-reactive protein, interleukin 6, leptin, white blood cell counts, neutrophils and the inflammatory biomarker score were observed. These relationships survived adjustment for demographic variables and health conditions but were attenuated in models which included lifestyle factors and BMI. In final models, only leptin (β = 0.566, p = 0.018) and inflammatory score (β = 0.137, p = 0.004) associations with the CES-D score remained. Conclusions: These findings suggest that the relationship between systemic low-grade inflammation and depressive symptoms and well-being may be largely explained by lifestyle factors and adiposity, highlighting the potential importance of promoting a healthy lifestyle in the treatment of depressive disorders.