Just how dangerous is obesity? A new report from Boston University and the University of Pennsylvania has expressed concern that some studies have underestimated the threat.
Published in the Proceedings of the National Academy of Sciences (2016; 113 , 572–77), the report challenges one research approach in particular: the single-observation study. This type of study relies on a one-time “snapshot” of body mass index and does not take into account whether subjects have weighed more at other times. As a result, says the report, researchers may have miscalculated the mortality risk associated with obesity.
Why? Because studies that do not distinguish between people who never exceeded normal weight and people of normal weight who were formerly overweight or obese fail to account for the enduring effects of prior obesity and ignore the fact that weight loss is often linked to illness. The resulting bias has led some studies to conclude that excess weight has a protective effect.
Amid this controversy, the BU and Penn researchers wanted to examine the topic more closely. They gathered data on “weight at time of survey” and “lifetime maximum weight” from the 1988–2010 National Health and Nutrition Examination Survey (which recorded both) and then compared results with death records through 2011, using various models.
Weight at time of survey proved to be a poor predictor of mortality; models using maximum lifetime weight were more accurate. In light of these findings, the authors urged more researchers to use weight history and not just a single weight snapshot when predicting mortality risk.
“Weight histories contain valuable information about mortality risks for at least two reasons,” they explained. “One is that obesity at a particular age may predispose to illness, regardless of weight at higher ages. The second is that weight loss is often associated with illness. These two mechanisms would lead to different patterns of association between weight change and mortality.”
The bottom line?
“Our results suggest the burden of overweight and obesity on mortality is likely substantially larger than commonly appreciated,” the study authors stated. “If correct, this may have serious implications for the future of life expectancy in the United States.”
To read the full report, go to www.pnas.org/content/113/3/572.full.
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