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January 15, 2018

Penn study: Improvements in U.S. mortality rate offset by obesity

Public Health Obesity
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A buffet line.

The rate of adult obesity has risen dramatically in the United States in recent decades, surpassing 36.5 percent of Americans and contributing to an uptick in otherwise preventable deaths from associated medical conditions, according to the Centers for Disease Control and Prevention. 

New research out of the University of Pennsylvania underscores just how much of an impact obesity has had on the country's mortality rates and overall life expectancy, which already falls outside the top 25 countries in the world. 

Obesity in the United States has offset some of the public health gains from advances in medical treatment and a reduction in the number of people who smoke. 

"We estimated that the impact of rising obesity was about twice as important for mortality trends as the impact of declining smoking," said lead researcher Samuel Preston, a sociology professor in Penn's School of Arts and Sciences. "Smoking is such an important variable in mortality analysis, and U.S. mortality is improving faster than it otherwise would because of reductions in smoking, but it's not improving fast enough to offset the effect of obesity." 

Penn demography student Yana Vierboom and Boston University global health researcher Andrew Stokes also joined the study, which took a unique approach to evaluating the effect of Body Mass Index on mortality. Rather than record BMI at baseline, the team looked at the maximum BMI for every subject in a demographic dataset including more than 25,000 people between 40-79 years old. 

This alternative measure enabled the researchers to better predict mortality by removing the mortality bias of weight loss associated with illness. It also allowed researchers to key in on the question of how weight history influences long-term health. 

Data used in the study was taken from successive cohorts of the National Health and Nutrition Examination Survey — from 1988-1994 and 1999-2010 — and from mortality files attached to the same records through 2011. 

Preston and his colleagues estimate that the mortality decline in the U.S. would have been about a half-percentage-point faster than it was had there not been such a sharp increase in obesity. 

The study looked at how many additional years beyond 40, finding that the increase in BMI accounted for a .9-year decrease in life expectancy beyond 40 years old during the period under review. 

"These results underscore the importance of the obesity epidemic for American health and mortality," Preston said. "When it's having this large an impact on the national level of vital statistics, it puts the spotlight on the importance of stopping and reversing the rise in obesity."

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