Tuesday, February 23, 2016

BU study: Effects of obesity on death rates understated in prior research

http://www.eurekalert.org/pub_releases/2016-01/bumc-bse010416.php

Public Release: 4-Jan-2016
BU study: Effects of obesity on death rates understated in prior research
Boston University Medical Center

Researchers from the Boston University School of Public Health and the University of Pennsylvania have found that prior studies of the link between obesity and mortality are flawed because they rely on one-time measures of body mass index (BMI) that obscure the health impacts of weight change over time.

The study, published online in the journal Proceedings of the National Academy of Sciences, maintains that most obesity research, which gauges weight at only a single point in time, has underestimated the effects of excess weight on mortality. Studies that fail to distinguish between people who never exceeded normal weight and people of normal weight who were formerly overweight or obese are misleading because they neglect the enduring effects of past obesity and fail to account for the fact that weight loss is often associated with illness, the researchers said.

When such a distinction is made, the study found, adverse health effects grow larger in weight categories above the normal range, and no protective effect of being overweight is observed.

"The risks of obesity are obscured in prior research because most of the studies only incorporate information on weight at a single point in time," said lead author Andrew Stokes, assistant professor of global health at BUSPH. "The simple step of incorporating weight history clarifies the risks of obesity and shows that they are much higher than appreciated."

Stokes and co-author Samuel Preston, professor of sociology at the University of Pennsylvania, tested a model that gauged obesity status through individuals' reporting of their lifetime maximum weight, rather than just a 'snapshot' survey weight. They found that the death rate for people who were normal weight at the time of survey was 27 percent higher than the rate for people whose weight never exceeded that category.

They also found a higher prevalence of both diabetes and cardiovascular disease among people who had reached a higher-than-normal BMI and then lost weight, compared to people who remained in a high BMI category.

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Of those in the normal-weight category at the time of the survey, 39 percent had transitioned into that category from higher-weight categories.

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A number of past studies have shown that people who lose weight have higher rates of death than those who maintain their weight over time. Part of the reason for that disparity is that illness may be a cause of weight loss, through decreased appetite or increased metabolic demands. Few studies have adequately accounted for that source of bias, Stokes and Preston noted.

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