Inflammation Could Explain Why Poor, Uneducated Suffer More CVD

Lisa Nainggolan

November 21, 2007 (Ann Arbor, MI ) – US researchers have found that people of lower socioeconomic position have a higher inflammatory burden in terms of interleukin-6 (IL-6) and C-reactive protein (CRP) than those of a higher socioeconomic position [1]. Dr Nalini Ranjit (University of Michigan, Ann Arbor) and colleagues report their findings in the November 20, 2007 issue of Circulation.
CRP and IL-6 are inflammatory markers linked to atherosclerosis, and "this study helps to explain some of the puzzle as to why poor people have more heart disease," says Ranjit. She told heartwire that the results should spur health educators and doctors to "target low-income people more specifically."
Ranjit and colleagues also found that adiposity was the single most important factor explaining the role of socioeconomic positioning on inflammatory markers, especially among blacks and whites. She believes that people of a lower socioeconomic status in the US "are structurally led into lifestyles that encourage adiposity, and that probably results in the inflammation."
Increase in CRP With Lower Socioeconomic Position "Small" but Important
Ranjit et al explain that associations of low socioeconomic position with higher inflammatory markers have been reported in European populations, but US studies are limited. One US study has failed to find any association of poverty with low-grade inflammation, and the two other US studies have focused on restricted samples (the mostly white Framingham Offspring Study and a sample of well-functioning adults aged 70 to 79 years).
Their cross-sectional study used data from the baseline examination of the diverse Multi-Ethnic Study of Atherosclerosis (MESA), which included 6814 men and women aged 45 to 84 years of age. Of the participants, 38% were white, 28% were African American, 22% were Hispanic, and 12% were Chinese.
They examined associations between two socioeconomic position measures--household income and education--with IL-6 and CRP, before and after adjustment for infection and medication use, psychosocial factors, behaviors, adiposity (waist circumference and body-mass index [BMI]), and diabetes mellitus. Average household income was $51 500, and average education was 13.6 years.
Low income was associated with higher concentrations of IL-6 and CRP in all ethnic groups studied--a drop in income of approximately $40 000 corresponded to 6% to 9% higher IL-6 and CRP (depending on race/ethnic group), with the largest association seen among whites.
In contrast, associations of education with these inflammatory markers were inconsistent across ethnic groups--among whites and blacks, each level of education one standard-deviation (SD) unit lower corresponded to 6% to 14% higher levels of IL-6 or CRP, whereas no association between education and inflammation was seen among Hispanic and Chinese subjects. However, when the researchers restricted their analysis to English-speaking Hispanics, they found that the effect size was comparable to that observed in whites and blacks.
Although the size of the associations "may appear small," say Ranjit et al, they note that the effects observed in whites--a 14% higher CRP associated with a 1-SD decrease in education and income--are equivalent to the difference in CRP associated with a 1.7 kg/m2-higher BMI. Alternatively, a CRP difference of 14% is approximately equivalent to the CRP reduction seen with statin therapy, they note.
Obesity: The Single Most Important Factor Explaining Observations
When the researchers examined covariates singly for each race/ethnic group, they found adiposity to be consistently the most important mediator of associations among blacks and whites for both socioeconomic position measures--income and education.
"Adiposity varies much more by socioeconomic status among blacks and whites than among Hispanics and Chinese," Ranjit explained to heartwire. She added that both Hispanic and Chinese participants "had very little variation in their BMI--most of the Chinese had low BMI, and the large majority of Hispanics had high BMI.
"Our results suggest that persons of lower socioeconomic position have greater inflammatory burden than those of high socioeconomic position as a result of the cumulative effects of multiple behavioral, psychosocial, and metabolic characteristics."
Ranjit told heartwire that it is possible that poor diets leading to adiposity make people more susceptible to infection, which ultimately leads to chronic low-level infection and the higher levels of inflammatory markers seen in people of lower socioeconomic position in this study. However, this requires confirmation, she notes.
"Our public-health messages should probably target poorer people," she says. "Sometimes lifestyles force things on you. If you are working all day or working weird shifts, you don't have time to cook yourself a proper meal and you end up eating at McDonald's." She added that this is "an intergenerational thing," with poorer children tending to eat the same kind of diet as their parents.
Ranjit N, Diez-Roux AV, Shea S, et al. Socioeconomic position, race/ethnicity and inflammation in the multiethnic study of atherosclerosis. Circulation 2007; 116:2383-2390.