The Concept of CMR

BMI: a weak correlate of metabolic syndrome abnormalities

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According to international guidelines, obesity is defined as a BMI of 30 kg/m² or more (24). BMI is commonly used as a valuable index of relative body weight and a crude estimate of total adiposity (25). Although of great use in estimating overall obesity, this clinical tool has serious limitations. First, the index assumes that weight is distributed evenly over the body (1) and does not take into account the heterogeneity of obesity (16). For example, individuals with large muscle mass but without excess body fat (e.g., American football and ice hockey or rugby players) could be misclassified as having a high-risk body weight. In addition, BMI does not provide information on body fat location, which has been shown to be a critical correlate of metabolic disturbances leading to CVD (26). In this regard, several studies relating BMI to CVD outcomes in healthy individuals have reported inconsistent results. Some studies have found a linear relationship between BMI and cardiovascular risk, whereas others have failed to find an association (20, 21, 27-29). However, most studies on the issue have not measured abdominal adiposity. In the Heart Outcomes Prevention Evaluation (HOPE) prospective study conducted in men and women with stable CVD, Dagenais et al. (30) found that BMI was no longer an independent predictor of myocardial infarction after adjusting for abdominal obesity indices such as waist-to-hip ratio (WHR) and waist circumference. Moreover, after adjusting for traditional risk factors such as BMI, waist circumference and WHR were independent predictors of CVD death, myocardial infarction, and total mortality (30). Other studies carried out in subjects without known CVD have also reported that WHR and waist circumference were better predictors of coronary heart disease than BMI (20, 31). For example, a 13 year follow-up study of 792 men reported that a high WHR increased ischemic heart disease risk while indices of total obesity had no predictive value (21). The authors concluded that although the association between WHR and CVD risk was not significant in multivariate analyses when cholesterol levels and blood pressure were taken into account, WHR was more closely related to CVD risk than other indices of obesity such as skinfold thickness or BMI (21). An additional prospective study conducted in women also reported similar findings (20).

Reference

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1. Bray GA, Bouchard C and James WPT, eds. Handbook of obesity. New York: Marcel Dekker. 1998.

16. Després JP, Lemieux I and Prud'homme D. Treatment of obesity: need to focus on high risk abdominally obese patients. BMJ 2001; 322: 716-20.

20. Lapidus L, Bengtsson C, Larsson BO, et al. Distribution of adipose tissue and risk of cardiovascular disease and death: a 12 year follow up of participants in the population study of women in Gothenburg, Sweaden. BMJ 1984; 289: 1261-3.

21. Larsson B, Svardsudd K, Welin L, et al. Abdominal adipose tissue distribution, obesity, and risk of cardiovascular disease and death: 13 year follow up of participants in the study of men born in 1913. BMJ (Clin Res Ed) 1984; 288: 1401-4.

24. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults--The Evidence Report. National Institutes of Health. Obes Res 1998; 6 Suppl 2: 51S-209S.

25. Garrow J and Summerbell C. Meta-analysis on the effect of exercise on the composition of weight loss. Int J Obes Relat Metab Disord 1994; 18: 516-7.

26. Kissebah AH, Freedman DS and Peiris AN. Health risks of obesity. Med Clin North Am 1989; 73: 111-38.

27. Wilson PW, D'Agostino RB, Sullivan L, et al. Overweight and obesity as determinants of cardiovascular risk: the Framingham experience. Arch Intern Med 2002; 162: 1867-72.

28. Wannamethee SG, Shaper AG, Walker M, et al. Lifestyle and 15-year survival free of heart attack, stroke, and diabetes in middle-aged British men. Arch Intern Med 1998; 158: 2433-40.

29. Stevens J, Cai J, Pamuk ER, et al. The effect of age on the association between body-mass index and mortality. N Engl J Med 1998; 338: 1-7.

30. Dagenais GR, Yi Q, Mann JF, et al. Prognostic impact of body weight and abdominal obesity in women and men with cardiovascular disease. Am Heart J 2005; 149: 54-60.

31. Folsom AR, Stevens J, Schreiner PJ, et al. Body mass index, waist/hip ratio, and coronary heart disease incidence in African Americans and whites. Atherosclerosis Risk in Communities Study Investigators. Am J Epidemiol 1998; 148: 1187-94.

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