Relationship of total and abdominal adiposity with CRP and IL-6 in women
Introduction
The prevalence of obesity has steadily increased over the last several decades, particularly in women (1). While much of the cardiovascular risk attributable to obesity may be mediated through effects on blood pressure, lipids, and glucose tolerance, some of this risk may be mediated by inflammatory pathways. Adipocytes secrete interleukin-6 (IL-6) 2., 3., one of the chief determinants of hepatic C-reactive protein (CRP) production (4). Some have reported that abdominal adipose tissue, as opposed to subcutaneous depots, may have higher secretion levels of IL-6 (5). Higher levels of CRP have been reported in obese individuals 6., 7., 8., but the relationship between CRP and body mass index (BMI) in the normal weight range has not been well-characterized. In addition, few studies (6) have examined whether abdominal adiposity is associated more strongly with CRP levels than measures of total adiposity, such as BMI. Additionally, few studies have examined whether IL-6 mediates the risk of elevated CRP associated with obesity.
The purpose of this study was to examine the association between anthropometry and risk of elevated CRP and IL-6 in women, using both measures of total adiposity (BMI) as well as measures of abdominal adiposity, including waist circumference (WC) and waist-hip ratio (WHR). In addition, we wished to determine whether the higher risk of elevated CRP among heavier women might be mediated by IL-6 and whether there was any potential effect modification by postmenopausal hormone therapy (HT).
Section snippets
Methods
This cross-sectional study was conducted among controls from two plasma substudies in the Women's Health Study, an ongoing randomized, double-blind, placebo-controlled trial of 39,876 female health professionals age 45 and older designed to determine the effects of low-dose aspirin and vitamin E in the primary prevention of cardiovascular disease and cancer. The design and cohort of the WHS is described in detail elsewhere (9).
Women enrolled in the WHS completed a baseline questionnaire which
Results
The characteristics of women with elevated CRP levels (⩾75th percentile: ⩾0.59 mg/dl) are presented in Table 1. Women with elevated CRP had higher BMI, WC, and WHR. In addition, they were more likely to be current HT users and to have a history of hypertension. Women with elevated IL-6 (⩾75th percentile: ⩾2.05 pg/ml) had higher BMI, WC, and WHR, and were more likely to smoke and less likely to use HT. They were also more likely to have a history of hypertension.
Figure 1 shows the relationship
Discussion
We found that both CRP and IL-6 levels were strongly correlated with BMI, not just at higher levels but throughout the full spectrum of BMI. Both inflammatory markers were also strongly associated with waist circumference, but more weakly associated with WHR. Risks associated with measures of abdominal adiposity were not independent of total adiposity, as measured by BMI. Among the adiposity measures that we studied, BMI was the strongest predictor of elevated inflammatory markers. The
Acknowledgements
The Women's Health Study is supported by grants CA-47988 and HL-43851 from the National Institutes of Health.
The authors would like to acknowledge the crucial contributions of the entire staff of the WHS, under the leadership of David Gordon, as well as Susan Burt, Mary Breen, Marilyn Chown, Lisa Fields-Johnson, Georgina Friedenberg, Inge Judge, Jean MacFadyen, Geneva McNair, David Potter, Claire Ridge, and Harriet Samuelson. We would also like to thank Anna Klevak and Rimma Dushkes for their
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