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Medicine & Science in Sports & Exercise:
BASIC SCIENCES: Epidemiology

Body Mass Index, but Not Physical Activity, Is Associated with C-Reactive Protein

RAWSON, ERIC S.1; FREEDSON, PATTY S.1,2; OSGANIAN, STAVROULA K.1; MATTHEWS, CHARLES E.3; REED, GEORGE1; OCKENE, IRA S.1

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Abstract

RAWSON, E. S., P. S. FREEDSON, S. K. OSGANIAN, C. E. MATTHEWS, G. REED, and I. S. OCKENE. Body Mass Index, but Not Physical Activity, Is Associated with C-Reactive Protein. Med. Sci. Sports Exerc., Vol. 35, No. 7, pp. 1160–1166, 2003. Elevated high-sensitivity c-reactive protein (hs-CRP) is associated with increased risk of future first and recurrent coronary events and has been associated with both high body mass index (BMI) and low physical activity in cross sectional studies.

Purpose: To longitudinally examine the effects of BMI and both current and previous-year physical activity on hs-CRP in healthy men and women (N = 109).

Methods: BMI and hs-CRP were measured five times (baseline and quarterly) over 1 yr. Current physical activity was assessed 12–15 times during the study via 24-h recall. Previous-year physical activity was assessed using the Baecke questionnaire at baseline.

Results: Mean BMI and hs-CRP were unchanged over the course of the study, but current physical activity increased on visit 3. Average hs-CRP was not related to average current physical activity or to natural changes in current physical activity across the five visits. Additionally, current physical activity on any given visit was not associated with hs-CRP on the following visit. When current physical activity, BMI, age, gender, and smoking were included in the statistical model, only BMI was significantly related to hs-CRP (P < 0.001). Average hs-CRP was significantly correlated with average BMI (r = 0.50; P < 0.001) but was not related to previous-year (Baecke) physical activity levels (r = 0.02; P = 0.89). When subjects were grouped by BMI (<25 kg·m−2, 25–29.9 kg·m−2, >30 kg·m−2) hs-CRP was significantly greater in obese (3.2 ± 1.9 mg·L−1) and overweight (2.1 ± 1.7 mg·L−1) than normal weight (1.1 ± 1.0 mg·L−1) subjects (ANOVA P < 0.05). Current physical activity was similar between the three BMI groups at all times, and was unrelated to hs-CRP in all groups, throughout the study period.

Conclusion: These data indicate that BMI, but not previous-year or current physical activity, predicts hs-CRP.

Inflammation plays a significant role in the pathogenesis of coronary heart disease (26). Apparently healthy individuals with increased high-sensitivity c-reactive protein (hs-CRP), a sensitive marker of inflammation, have an increased relative risk of future first cardiac events even after adjustment for age, smoking status, body weight/body mass index (BMI), hyperlipidemia, and hypertension (11,12,19–23). In fact, the relative risk of increased hs-CRP is greater than and independent of traditional (cholesterol, HDL, LDL) and novel (lipoprotein (a), homocysteine, apolipoproteins AI and B) markers of cardiovascular risk (24). Cholesterol screening fails to identify 50% of the individuals who have myocardial infarctions in the United States each year, because their total cholesterol values are either normal or only moderately increased (24). Thus, the factors that may influence hs-CRP in a healthy adult population are important to identify.

The positive relationship between increased BMI and increased hs-CRP has been well documented (7,29), but the mechanism by which BMI can influence hs-CRP is unclear. It has been proposed that the overweight and obese states are associated with increased hs-CRP because they are reflective of low-grade systemic inflammation (29). Recently, it was reported that hs-CRP decreases after significant weight loss (28), which further demonstrates the influence of body size on hs-CRP. Cross-sectional studies indicate that increased levels of physical activity are associated with reduced hs-CRP levels (9,10), and one exercise intervention study reported a trend for reduced hs-CRP after 6 months of exercise training (27). However, the interactions between BMI, physical activity, and hs-CRP are unclear. To our knowledge, there are no longitudinal data available that include multiple measurements of BMI, physical activity, and hs-CRP. Additionally, the influence of current versus previous-year physical activity on hs-CRP has not been reported. The purpose of this investigation was to examine the effects of BMI, current physical activity, and previous-year physical activity on hs-CRP concentrations in apparently healthy adult men and women. We hypothesized that 1) BMI would be a significant predictor of hs-CRP and 2) physical activity would be a significant independent predictor of hs-CRP.

©2003The American College of Sports Medicine

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