The body mass index (weight in kg divided by the square of height in metres) remains the standard way of assessing weight by the medical profession. The problem is, as I’ve pointed out previously, (for example, here and here) it is a generally useless measure as a marker for health.
In previous pieces, I have presented evidence that a better marker for health and disease is the ‘waist-to-hip ratio’ (WHR). Weight that accumulates around the middle of the body, as opposed to weigh distributed elsewhere, does seem to have a link with chronic diseases such as heart disease and diabetes.
The most recent research to examine the relationship between body weight and shape and disease risk was published this week in the Journal of the American College of Cardiology [1]. More than 2700 men and women had their waist-to-hip ratios and BMIs measured, and this was compared to their risk of disease in the arteries. Two techniques were used to assess coronary artery disease: electron beam computed tomography (design to measure calcium build-up in the coronary vessels) and MRI scanning (which measured fatty build-up – atherosclerosis – in the body’s major artery – the aorta). Deposition of calcium in an artery is generally taken to be an early indicator of vessel disease and potential cardiovascular problems including heart disease.
The researchers split up the study participants into 5 what are known as ‘quintiles’ for BMI and WHR. The first quintile is made up with the 20 per cent of participants with the lowest BMIs/WHRs, while the 5th quintile contains those with the highest BMIs/WHRs. With me so far?!
The results of this study found that increasing BMI was not a strong predictor of atherosclerosis risk. In fact, individuals needed to be in the fifth quintile of BMI for this to be associated with a significantly increased risk of atherosclerosis compared to those in the first quintile.
However, the WHR turned out to have a strong association with the markers for heart disease measured. For instance, those in the 2nd WHR quintile were already at a statistically significant increased risk of calcium deposition compared to those in the first quintile. And those in the fifth quintile of WHR were found to be about 90 per cent more likely to have calcium deposition compared to those in the first quintile. Similar relationships were found between WHR and atherosclerosis too.
As the authors of this study point out, these results mirror those of other work looking at the relationship between BMI/WHR and overt cardiovascular disease. For example, one study published in 2005 spanning 52 countries found that BMI had no significant bearing on heart attack risk, while WHR did appear to have a strong association with this measure of health [2].
It is often recommended that the waist to hip ratio should, ideally, not exceed 0.90 and 0.83 for men and women respectively. An alternative measurement that is simpler and appears to be also useful is just the waist circumference. The results of this most recent study suggest that cut-off points for waist circumference are 32 inches (81 cm) and 37 inches (94 cm) for women and men respectively. Taking steps to combat weight accumulation around the middle seems like it might help keep our health from going to pot.
References:
1. See R, et al. The Association of Differing Measures of Overweight and Obesity With Prevalent Atherosclerosis. The Journal of the American College of Cardiology 2007; 50:752-759
2. Yusuf S, et al. Obesity and the risk of myocardial infarction in 27,000 participants from 52 countries: a case-control study. Lancet 2005;366(9497):1640-9
