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Tuesday, 11 September 2012

Waistline and increased risk of premature death: what's so new?

@HealthMed The latest European Society of Cardiology Congress in Munich coincided with the last days of a Gallery of the Modern exhibition of caricatures by Munich satirist Karl Arnold:  amongst them a striking 1922 image of a stylish corpulent man said for 20 years not to have been able to see his feet. Then a social observation, it is of course now well recognized that the frankly obese are at high risk of diabetes, heart disease, stroke and other medical conditions.

At first sight surprising, that there should have been major interest from scientists and the press in new US research presented at the 2012 heart Congress linking a larger waistline to premature death; and not just from a beer belly, but for anyone with a body shape with above normal waist to hip circumference.  What’s so unusual? Surely everyone knows that being overweight increases risk of serious medical problems.

What did these American researchers do? They looked at the strength of the link between different measures of obesity and risk of early death. In the research, lead by Professor  Francisco Lopez-Jimenez from the Mayo Clinic, almost 13,000 American men and women were studied for around 14 years, within a cohort study: the Third National Health and Nutrition Examination Survey (NHANESIII). There were around 2500 deaths of which around 1100 were from cardiovascular causes. The researchers measured body-mass index (BMI), a general measure of fatness, and waist-to-hip ratio (WHR), a measure of central obesity. This meant they were able to include people not currently considered obese based on BMI, but who had a relatively large belly, as well as those overweight both based on BMI and abdominal girth. The surprising finding of the study was that, compared to subjects with normal BMI and WHR, the group with normal BMI but relatively high central fat not only had a high death rate (2.8 times for cardiovascular disease and 2.1 times for all causes), but their risk of premature death was much higher than participants who were obese based on BMI (1.4 times normal cardiovascular risk).

It is already well established that abdominal fat is particularly deadly in relation to risk of heart disease. This new NHANESIII research in addition reported that increasing waist-hip ratio is linked to earlier death from all causes, not just for heart disease. It also provided objective data of the graded increase in risk as abdominal fat and waist-hip ratio increases.

What messages to take from this study? Obvious questions include whether it is reliable and if so generalizable from US to European and other international populations. As a prospective observational study, the results are open to bias – i.e. factors co-incidentally present in the larger waisted people may have been responsible e.g. the type of diet causing the central overweight rather than distribution of the fat itself.

However the authors reported that their findings were similar after adjusting for other well-known risk factors for premature heart disease and death, such age, male gender, ethnicity, socio-economic factors, smoking, hypertension, and diabetes.  Furthermore, this new report from Munich supported the previous systematic review by the authors noting similar findings in patients with coronary artery disease: i.e. central obesity a much stronger link  than BMI to premature death.

Reasons for the observed health risks are thought to include major regional differences in types chemicals secreted by fat from different parts of the body. Unlike fat padding in other part of the body, abdominal (or visceral fat) makes chemicals that promote resistance to insulin, increasing risk of diabetes, an important risk factor for heart disease. This fat also makes inflammatory chemicals that can accelerate damage to arteries, leading to atheroma (deposits of fat and abnormal cells – from the Greek for ‘porridge lump’) in the arterial walls. This both reduces blood flow to vital organs, and increases the likelihood of a clot forming to cause critical narrowing or complete blockage of an artery, a major cause of heart attack and stroke. There is also  evidence that in contrast there may also be a protective metabolic profile associated with the presence of lower body fat.
These findings add to increasing concern about health risks from central overweight and stress the importance of preventive measures, even if BMI is within the normal range. Health professionals need to make the public aware of these risks and explain what preventive measures may help. The good news is that losing excess central weight is practical through a healthy, lower calorie diet, combined with regular aerobic exercise, reduces major risk factors for heart disease: reduces cholesterol, decreases blood pressure and reduces risk of diabetes, and lowers risk of heart and other serious diseases. Other reasons for benefits may include better metabolic profile from the increase in muscle mass with exercise, and the improved tissue nutrition resulting from generation of more micro-vessels.
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