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Obesity paradox

Obesity paradox studies are flawed claim researchers

Dr Ryan Masters lead author of the study
Study claims ibesity paradox is a mirage
As obese people grow older, their risk of death increases

Previous studies that claim the obesity epidemic is overhyped are flawed, according to new research published in the American Journal of Epidemiology.

"This study should put to rest the notion that it's possible to 'age out' of obesity risk, and provides a powerful counterfactual against those who say concern over obesity is overhyped," said Dr Bruce Link, professor of Epidemiology and Sociomedical Sciences, Mailman School, Columbia University.

Previous research has reported that the obesity paradox claims people aged 65 and older, and who have an elevated BMI, may live longer. However, the study claims that the so-called obesity paradox is a mirage, and as obese people grow older, their risk of death increases.

In the analysis the investiagtors matched US National Health Interview Survey data on obesity with corresponding records in the National Death Index using data from some 800,000 adults surveyed between 1986 and 2004. They examined age patterns in the obesity-mortality association between ages 25 and 100 years, via a series of Cox regression models to account for the survey selection biases.

Their findings suggest that survey-based estimates confounded by disparate cohort mortality and age-related survey selection bias. When these factors are accounted for in Cox survival models, the obesity-mortality relationship is estimated to grow stronger with age.

The researchers argue that past studies of longevity and obesity were biased due to limitations of the National Health Interview Survey. The survey excludes individuals who are institutionalised, such as in a hospital or nursing home, a group largely made up of seniors.

As a result, the data is overrepresented by older individuals who are healthy, including the relatively healthy obese. This is compounded by the fact many obese individuals fail to make it to 65 years, and therefore do not live long enough to participate in studies of older populations.

"Obesity wreaks so much havoc on one's long-term survival capacity that obese adults either don't live long enough to be included in the survey or they are institutionalized and therefore also excluded,” said Dr Ryan Masters, Robert Wood Johnson Foundation Health & Society Scholar, Mailman School, lead author of the study. “In that sense, the survey data doesn't capture the population we're most interested in."

Next, Masters said that he will investigate why some of the older obese captured in NHIS data only put on extra weight later in life.

"The recent obesity epidemic hit all age groups at the same time, meaning many of the elderly obese only gained their excess weight in the last ten years or so," said Masters. "To account for this fact, I will take a page from studies of cigarette smokers by looking at 'life years' to measure how long someone has been obese rather than whether or not they happen to be obese at the time of a single snapshot survey."

Dr Daniel Powers, University of Texas, was a co-author of the study.

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