A Beer Belly Trumps a Raised BMI in Predicting Heart Trouble

The importance of an increased waist circumference as a risk factor for cardiovascular disease has been discussed on this blog several times before.  Now data on confirmation and quantification of the risk have been analyzed by an international team led by Mayo Clinic researchers in the Journal of the American College of Cardiology. 

The data came from medical publications in which information was available for: coronary artery disease at baseline, waist circumference or waist/hip ratio, body mass index (BMI), and mortality in the coronary disease patients.  Five published and one unpublished study yielded the necessary information on 15,900 people; 2,396 were obese (BMI 30 or above) and 6,648 had a normal BMI. Average follow-up was 2.3 years.  There were 5,696 deaths.

The subjects were allocated to two sets, each having 3 classes (tertiles) – high, medium, and low. One set was termed Central Obesity, using tertiles for waist circumference and waist/hip ratio.  The other set used BMI to build tertiles.  Mortality was compared between the highest and lowest tertile in both sets. 

Central obesity was associated with a 70% increase in the risk of mortality, regardless of BMI.  On the other hand, increasing BMI was associated with a lower risk – the so-called “obesity paradox”.  This apparent protective effect of an increasing BMI was trumped, however, by central obesity; the latter was associated with higher mortality both in obese patients (i.e. BMI over 30) and in those with a normal BMI – increases of 93% and 70%, respectively. 

This analysis shows that BMI, although widely used, isn’t a good measure of the increased risk associated with excess fat accumulation.  Waist circumference or the waist/hip ratio is a simple and superior measure, because it represents the fat in the belly, compared with that in the thighs or upper arms.  An expert concludes, in an accompanying editorial, that BMI shouldn’t be disregarded completely – attention should be paid to waistlines that are “exaggerated” for the corresponding BMI, especially if it’s accompanied by raised blood triglyceride levels.