25 May 2012

Obesity not always tied to higher heart risk

An obese person isn't inevitably at increased risk of cardiovascular disease and death, a new UK study finds.


An obese person isn't inevitably at increased risk of cardiovascular disease and death, a new UK study finds.

"The people really at risk are the ones who have obesity in combination with other metabolic health risk factors," said Dr Mark Hamer, a principal research associate at University College London who worked on the study with his colleague Dr Emmanuel Stamatakis.

The results are in line with most previous research that defined metabolic health as having normal levels of markers like blood pressure, blood glucose, high density lipoprotein cholesterol, and C-reactive protein.

"People with good metabolic health are not at risk of future heart disease" – even if they are obese, Dr Hamer said. On the flip side, the non-obese in poor metabolic shape face as much risk as the unhealthy obese, the researchers concluded.

Obese people encouraged to lose weight

The findings, published online in the Journal of Clinical Endocrinology & Metabolism, are based on more than 22 000 middle-aged participants in national health studies conducted in England and Scotland.

The researchers say the results suggest that metabolic factors may be more important in predicting a person's risk of cardiovascular disease than excess body weight in itself.

From a clinical perspective, stratifying individuals based upon their metabolic profile may help to identify those – both obese and non-obese – who should be treated with drugs or changes in diet and exercise, the study authors noted.

"We encourage obese people to lose weight for their health, but (some) provision should be made in how we screen people" for metabolic risk, Dr Hamer said.

An adult who has a body mass index of 30 or higher is considered obese. A normal BMI is between 18.5 and 24.9, and a BMI between 25 and 29.9 is considered overweight.

During the past 20 years, obesity has increased significantly in the United States. More than a third of American adults are obese, according to the Centres for Disease Control and Prevention.

Obese not at risk of cardiovascular disease

For the new report, the authors collected data on BMI and metabolic profiles and followed individuals, on average, for seven years. Then they looked at how many participants had died during the study period, and from what causes.

None of the participants had heart disease at the start of the study. But almost a quarter were obese, and just under a quarter of those were considered "metabolically healthy obese" – meaning they had normal blood pressure, cholesterol, glucose and CRP.

During the study period, more than 600 participants died from heart-related causes and 1,800 from other causes.

The obese individuals in good metabolic health were not at greater risk of dying from cardiovascular disease than the metabolically healthy non-obese, the researchers found.

Waist circumference used to define obesity

But both non-obese and obese participants in poor metabolic health had a 59% and 64% increased risk of dying from heart disease, respectively, compared to the healthy non-obese.

Among the metabolically unhealthy participants, the non-obese had high levels of hypertension and inflammation – comparable to those in the unhealthy obese group.

The metabolically unhealthy obese also had a 72% higher risk of dying from non-heart-related causes than those in good health.

That was after taking into account study participants' age, sex, smoking, physical activity and socioeconomic status.

Researchers found the results to be largely unchanged when they used waist circumference to define obesity instead of BMI.

Think broadly about obesity

Dr Hamer and his colleague note in their report that strength of their study was having a large study population. But because they only measured participants' metabolic risk factors at the beginning of the study, it's possible that some of the metabolically healthy obese went on to develop unhealthy markers.

The study shows the need "to think more broadly about obesity" rather than to focus on body weight alone, said Dr Cora Lewis, a professor of preventive medicine and an epidemiologist at the University of Alabama, Birmingham, who was not involved in the research.

"If you are obese and you struggle with weight, but your (metabolic) risk factors are fine, that may not be such a bad place to be," Dr Lewis told Reuters Health – adding that only "a minority of people" fit the description of "metabolically-healthy obese."

(Aparna Narayanan, Reuters Health, May 2012) 

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