gms | German Medical Science

Background: There is growing evidence that beyond individual factors, community-level characteristics relate to the development and progression of chronic diseases. Persistent inflammation might act as an underlying mechanism. Study questions: We asked whether district-level socio-economic status is associated with C-reactive protein as an established non-specific biomarker of low grade inflammation and whether associations might be observed independently of individual-level factors including educational status, health-related behaviours, and measures of obesity.

Methods: This cross-sectional analysis used individual-level data from the National Health Interview and Examination Survey for Adults in Germany 2008-2011 (DEGS1) which is based on a nationwide representative sample of the population 18-79 years. Serum high-sensitivity C-reactive protein (hs-CRP) measures and individual-level covariables were available for 6,662 participants nested in 163 municipalities. Information on district-level net household income as a proxy variable for district-level socio-economic status was assigned to each study participant according to residential area. Associations between individual and district-level variables with serum levels of hs-CRP were assessed using two-level random-intercept linear regression models. Besides sex and age, the following independent individual-level variables were consecutively added to multivariable models: educational status; health-risk behaviours including smoking, sports activity, alcohol consumption; and body mass index (BMI). In additional analysis, waist circumference and preexisting chronic diseases including cardiovascular diseases and diabetes were also considered.

Results: District-level net household income was inversely related to hs-CRP measures. Adjusting for age and sex, a 13.3% lower geometric mean of hs-CRP levels was found among adults residing in districts with the highest tertile of net household income compared to those in the lowest tertile (p<0.001). Results were not materially changed after additionally adjusting for individual-level educational status and health-related behaviours. Additional inclusion of BMI attenuated the association between net household income and hs-CRP levels. An inverse association between individual-level educational status and hs-CRP was, however, only in part attenuated after further adjustment for health-risk behaviours and obesity. Similar results were obtained after additional inclusion of waist circumference and chronic diseases. Results were consistent after stratification by sex as well as after excluding individuals with hs-CRP levels above 10 mg/L (n=231). Conclusions: The observed association between district-level net household income and hs-CRP was apparently mediated by measures of obesity. The independent inverse relationship between individual educational level and low grade inflammation was, however, not fully explained by health-risk behaviours and obesity.

Practical implications: Health-risk behaviours and obesity might be of great importance in explaining area-level social disparities in chronic disease burden. However, additional factors (e.g. indicators of psychosocial stress) need to be considered in order to explain individual-level social disparities.