MRCGP exam update: Waist-to-hip ratio in CHD

Current situation?  

Obesity is an increasing problem worldwide.  

Abdominal obesity is one important risk factor for obesity and accounts for more than 90 per cent of the worldwide MI risk.  

Waist circumference is an alternative indirect measurement of body fat that reflects the intra-abdominal fat mass, which is strongly correlated with CHD risk, diabetes, hyperlipidaemia, and hypertension.  

Waist-to-hip ratio was the strongest predictor of MI in men and women, across all age and ethnic groups, in smokers and non-smokers and in those with or without dyslipidaemia, diabetes or hypertension.  

A large waist circumference is also a predictor for type-2 diabetes. Carrying excess fat, particularly deposition of visceral fat, is known to promote insulin resistance and other features of the metabolic syndrome.  

What is the evidence?  

The importance of intra-abdominal fat was underlined by new research which found that with increases in visceral fat, mortality increased by up to five-fold (Obes Res 2006; 14: 336). This increase was actually independent of BMI.  

A large case-control study (by the INTERHEART  investigators) of more than 27,000 people from diverse ethnic groups across the world has shown conclusively that waist-to-hip ratio is the best measure for assessing CHD risk and BMI is the worst measure  (Lancet 2005; 366: 1,640).  

One prospective study on the risk of death in patients with acute MI identified abdominal obesity as measured by the waist-to-hip ratio as a better risk indicator than BMI (Int J Cardiol 2005; 98: 123).  

The opposing effects on cardiovascular risk between abdominal and lower-body fat tissue are probably related to different biochemical characteristics of fat in these regions and differences in secretion of adipokines that contribute to cardiovascular and metabolic risk (Obes Res 2004; 12: 1,217). 

Implications for practice  

The association of BMI with MI disappears when adjusted for the other risk factors, whereas the associations of waist, hip, and waist-to-hip ratio are still highly significant.  

If a raised waist-to-hip ratio (0.83 in women and 0.9 in men) were to be used to assess the risk of cardiovascular disease, the proportion of the population classified as obese worldwide would increase substantially.  

Available guidelines  

The main message from the INTERHEART report is that current practice with BMI as the measure of obesity is obsolete and results in considerable underestimation of obesity.     

Useful websites  

www.heartforum.org.uk — National Heart Forum  

www.library.nhs.uk —    National Library for Health  

Dr Louise Newson is a GP in the West Midlands and author of ‘Hot Topics for MRCGP’, Pas Test 2006 

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