Effects of obesity on death rates understated in prior research, study shows

January 4, 2016 by Lisa Chedekel, Boston University Medical Center
Credit: Peter Häger/Public Domain

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 research, which gauges weight at only a single point in time, has underestimated the effects of on mortality. Studies that fail to distinguish between people who never exceeded 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.

Stokes and Preston argue that using "weight histories" in studies of obesity and mortality is important for two reasons. One reason is that obesity at a particular age may predispose people to illness, regardless of subsequent weight loss. The other is that weight loss is often caused by illness.

The researchers used data from the large-scale 1988-2010 National Health and Nutrition Examination Survey, linking the data to death certificate records through 2011. The survey asked respondents to recall their maximum lifetime weight, as well as recording their weight at the time of the survey.

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

The study used statistical criteria to compare the performance of various models, including some that included data on weight histories and others that did not. The researchers found that weight at the time of the survey was a poor predictor of mortality, compared to models using data on lifetime maximum weight.

"The disparity in predictive power between these models is related to exceptionally high mortality among those who have lost weight, with the normal-weight category being particularly susceptible to distortions arising from weight loss," the researchers said. "These distortions make overweight and obesity appear less harmful by obscuring the benefits of remaining never obese."

The study comes amid controversy over the relationship between obesity and mortality, with some recent studies indicating that excess weight is a protective factor in health. One such study, a major meta-analysis in 2013 led by a researcher with the Centers for Disease Control and Prevention, indicated that being overweight was associated with lower mortality, and that slight obesity conferred no excess risk of death.

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 , through decreased appetite or increased metabolic demands. Few studies have adequately accounted for that source of bias, Stokes and Preston noted.

They urged more research using histories, saying such an approach had proven valuable in studies of smoking, which distinguish between former and current smokers and those who have never smoked.

Explore further: Researcher finds mortality risks of being overweight or obese are underestimated

More information: Revealing the burden of obesity using weight histories, Proceedings of the National Academy of Sciences, www.pnas.org/cgi/doi/10.1073/pnas.1515472113

Related Stories

Researcher finds mortality risks of being overweight or obese are underestimated

April 7, 2014
New research by Andrew Stokes, a doctoral student in demography and sociology in the School of Arts and Sciences at the University of Pennsylvania, suggests that many obesity studies substantially underestimate the mortality ...

Study says obesity doesn't protect patients with cardiovascular disease

October 12, 2015
Demographers Samuel Preston of the University of Pennsylvania and Andrew Stokes of Boston University set out to solve a puzzle: Why is it that study after study shows obese or overweight people with cardiovascular disease ...

Ultrasound can read weight of fetuses with FGR in obese moms

December 17, 2015
(HealthDay)—Sonographic (US) examination can accurately estimate fetal weight, even in overweight and obese women with singleton pregnancies affected by fetal growth restriction (FGR), according to research published in ...

To reduce risk of infant death, shed excess pounds before becoming pregnant

November 17, 2015
Achieving a healthy weight before becoming pregnant and gaining an appropriate amount of weight during pregnancy significantly reduce the risk of the baby dying in his or her first year of life, according to new research ...

New research says that increasing personal happiness produces easier weight loss

October 7, 2015
Many people believe that if they lose weight they will be happier about themselves, but new research by the University of Adelaide is suggesting people take the opposite approach.

MRI reveals weight loss protects knees

November 30, 2015
Obese people who lose a substantial amount of weight can significantly slow the degeneration of their knee cartilage, according to a new MRI study presented today at the annual meeting of the Radiological Society of North ...

Recommended for you

Lack of sleep leads to obesity in children and adolescents

April 16, 2018
Children who get less than the recommended amount of sleep for their age are at a higher risk of developing obesity.

Getting kids to a good weight by 13 may help avoid diabetes

April 4, 2018
There may be a critical window for overweight kids to get to a healthy level. Those who shed their extra pounds by age 13 had the same risk of developing diabetes in adulthood as others who had never weighed too much, a large ...

Obesity is shifting cancer to young adults

March 26, 2018
A Case Western Reserve University School of Medicine researcher has compiled evidence from more than 100 publications to show how obesity increases risk of 13 different cancers in young adults. The meta-analysis describes ...

Obesity rates keep rising for U.S. adults

March 23, 2018
Obesity rates have continued to climb significantly among American adults, but the same hasn't held true for children, a new government report finds.

Obesity trigger identified within the human gut

March 22, 2018
The key chemical for happiness and sadness, serotonin, is also a force in our body's weight gain and calorie control, and scientists say more research could reduce obesity rates.

How obesity dulls the sense of taste

March 20, 2018
Previous studies have indicated that weight gain can reduce one's sensitivity to the taste of food, and that this effect can be reversed when the weight is lost again, but it's been unclear as to how this phenomenon arises. ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.