Exploring the Relationship between Socioeconomic status and C-Reactive protein levels in the US population using NHANES Survey Data

Exploring the Relationship between Socioeconomic status and C-Reactive protein levels in the US population using NHANES Survey Data Abstract Background Several studies have examined the impact of socioeconomic status on health and its overall quality. Low socioeconomic status has been associated with a higher prevalence of chronic health conditions, mortality from coronary heart disease, stroke, diabetes and subclinical markers of disease risk. An elevated Plasma C-Reactive Protein (CRP) is one of such markers, signaling an increased risk for atherosclerotic cardiovascular disease and sub clinical stages of pulmonary dysfunction. Various studies have been carried out on the association between CRP levels and Socioeconomic status. However, most studies did not consider how factors like acute and chronic health conditions along with health behaviors relates with the socioeconomic difference in CRP levels. In addition, many of the study samples in the previous studies were not representative of the socioeconomic diversity of the United States. In this study, we explored the relationship between socioeconomic status and C-Reactive protein levels in the US population, taking account of health indicators and behavioral factors. Methods We used the National Health and Nutrition Examination Survey (NHANES) dataset from 2001 to 2006. The survey includes interviews, clinical examinations and laboratory test data. Demographic factors (age, ethnicity and poverty), health/immunity indicators (recent illness, leucocyte count, asthma, chronic bronchitis and rheumatoid arthritis) and behavioral risk factors (obesity, current smoker, heavy drinking and exercise) were examined in this study to see how they predict the socio economic variation in CRP levels. Blood samples from a total of 13,708 adults who were over 20 years were assayed for CRP. Pregnant women (888) and participants who did not have income data (1006) were excluded from the study. For our analysis, CRP were divided into three categories: moderate (1.01 – 3.0 mg/L), high (3.01 – 10.0 mg/L) and very high ([greater than] 10 mg/L). First, bivariate analysis was done to display the characteristics of the study population by poverty status. T-tests and Chi-square tests were used for continuous and categorical variables respectively. Multinomial logistic regression was then used to obtain the relative odds of having a CRP level that is above normal in relation to poverty. Results The mean levels of CRP and blood leucocyte count were higher for subjects in poverty. Subjects in poverty were more likely to be female and of a younger age. People in poverty had a higher prevalence of recent illness, asthma, chronic bronchitis, and rheumatoid arthritis. They also reported a higher prevalence of obesity, current smoking, heavy drinking and as well as less exercise. As age increased, the odds of all CRP levels compared to the normal increased. Obesity had the highest odds ratio (Moderate 2.81; 95% CI: 2.41 – 3.29; High 5.88; 95% CI: 4.96 – 6.96; Very high 8.51; 95% CI: 7.03 – 10.30) for CRP above normal levels. The odds of having very high CRP level was also increased for people with chronic bronchitis and rheumatoid arthritis. Controlling for the demographic factors, health indicators and behavioral factors, living in poverty increased the odds of very high CRP levels by 36% when compared to those not living in poverty. Conclusion Socioeconomic status is related to higher CRP levels, and this relationship is noteworthy at very high CRP levels. People who have low indicators of health and immunity are more likely to be in poverty and to have a very high CRP level. We found that the line depicting CRP level for those in poverty and above poverty crossed as age increased. Further studies need to be carried out on this subject to examine if there is an interaction effect between CRP levels and poverty at different age groups.