In our previous editorial, we reviewed the results of the large international observational study (IDEA) published in October 2007 [1]. This study provided evidence that waist circumference predicted diabetes and cardiovascular disease (CVD) prevalence in a sample of nearly 170,000 patients followed by primary care physicians in 63 countries worldwide. Although it was very large in size and clearly demonstrated the clinical relevance of measuring waist circumference, IDEA was cross-sectional in design and only assessed the prevalence of diabetes and CVD-associated abdominal obesity.
In an issue of Circulation published last December [2], investigators of the EPIC-Norfolk study reported results of a careful investigation of the relationship of waist and hip circumferences to coronary heart disease (CHD) incidence. EPIC-Norfolk is a large prospective study of a population-based sample of 24,508 men and women 45 to 79 years of age, who were followed for 9.1 years for incidence of CHD. The study is significant as 1,708 men and 892 women developed CHD over the course of follow-up. The authors found that increased waist circumference raised the risk of CHD, while increased hip girth seemed to confer some protection against CHD after adjustment for body mass index (BMI), age, systolic blood pressure, cholesterol, cigarette smoking, physical activity, and alcohol intake.
The finding that waist circumference was a predictor of CHD incidence confirms the powerful impact this index of abdominal obesity has on CVD risk. Several studies have previously shown that an increase in waist circumference increases CHD risk at any BMI level. For instance, the INTERHEART study comparing myocardial infarction cases with asymptomatic controls has clearly shown that an increased proportion of abdominal fat, as reflected by a high waist-to-hip circumference ratio, significantly increases the odds ratio for myocardial infarction [3]. In addition, several prospective observational studies [4-6] have shown that an increased waist circumference increases risk of CHD independent of and beyond the “effect” of BMI.
It has been suggested that the CVD risk resulting from an elevated waist circumference may be a marker of excess intra-abdominal (visceral) adiposity, which is predictive of insulin resistance and a pro-atherogenic, thrombotic, and inflammatory profile [7]. The expanded intra-abdominal fat depot acts as a large “endocrine gland” that becomes inflamed and generates an insulin resistant and pro-inflammatory state that helps increase CHD risk. However, an original and relevant finding of EPIC-Norfolk is that peripheral fat (after adjustment for BMI) is cardioprotective. This finding is fully consistent with the notion that lower body subcutaneous fat may act as a protective metabolic sink by buffering excess energy through storage and protecting other organs and coronary arteries against harmful lipid deposition [7]. When exposed to a surplus of calories, those of us who accumulate excess energy in lower body subcutaneous fat appear to be at lower risk of CHD, while those who cannot efficiently clear and store the energy in peripheral depots build up their intra-abdominal fat stores and increase their ectopic fat, a process leading to atherogenic metabolic disturbances that increase CHD risk.
By regressing waist values to CHD risk, the authors estimated that a 5 cm drop in waist circumference could reduce CHD risk by 11% in men and 15% in women. The authors also pointed out that reducing waist circumference by such an amount (5 cm) can certainly be achieved with moderate weight loss. For instance, as a rule of thumb, we often mention that a weight loss of 1 kg is associated with a reduction in waist circumference of approximately 1 cm. A weight loss of only 5 kg would therefore be enough to produce the reduction in CHD risk estimated by the EIPIC-Norfolk investigators. Although these observations should be considered indirect evidence, they fit with the notion that moderate weight loss (only 5 kg) can substantially reduce abdominal fat and produce clinical benefits [8]. Of course, intervention studies will be required to confirm these estimates.
In summary, this interesting paper from EPIC-Norfolk provides solid evidence that along with stethoscopes, measuring tapes should be on the list of simple clinical tools that physicians should use to evaluate their patients.
References
- Balkau B, Deanfield JE, Després JP, et al. International Day for the Evaluation of Abdominal Obesity (IDEA): a study of waist circumference, cardiovascular disease, and diabetes mellitus in 168,000 primary care patients in 63 countries. Circulation 2007; 116: 1942-51. PubMed ID: 17965405
- Canoy D, Boekholdt SM, Wareham N, et al. Body fat distribution and risk of coronary heart disease in men and women in the European Prospective Investigation Into Cancer and Nutrition in Norfolk cohort: a population-based prospective study. Circulation 2007; 116: 2933-43. PubMed ID: 18071080
- Yusuf S, Hawken S, Ounpuu S, et al. Obesity and the risk of myocardial infarction in 27,000 participants from 52 countries: a case-control study. Lancet 2005; 366: 1640-9. PubMed ID: 16271645
- Rexrode KM, Carey VJ, Hennekens CH, et al. Abdominal adiposity and coronary heart disease in women. JAMA 1998; 280: 1843-8. PubMed ID: 9846779
- Folsom AR, Kushi LH, Anderson KE, et al. Associations of general and abdominal obesity with multiple health outcomes in older women: the Iowa Women’s Health Study. Arch Intern Med 2000; 160: 2117-28. PubMed ID: 10904454
- Lakka HM, Lakka TA, Tuomilehto J, et al. Abdominal obesity is associated with increased risk of acute coronary events in men. Eur Heart J 2002; 23: 706-13. PubMed ID: 11977996
- Després JP and Lemieux I. Abdominal obesity and metabolic syndrome. Nature 2006; 444: 881-7. PubMed ID: 17167477
- 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. PubMed ID: 11264213