In what in many ways is a definitive study on the topic, a very large analysis of 1.46 million adults further confirms that overweight and obesity significantly increase the risk of mortality (study). The analysis by Berrington de Gonzalez and colleagues, which appears in the New England Journal of Medicine today, pooled together data from 19 prospective studies that followed participants over time – noting participant’s body mass index (BMI) and keeping track of participant deaths.
Because health status and smoking status can have an impact both on weight and mortality – sick people often lose weight, and smokers are often lean and prone to dying earlier than non smokers – researchers focused their analyses on participants who were both non-smokers and healthy at the study’s start. The goal was to get a truer reflection of the impact that weight could have on health.
What they found was that as BMI increased above the normal range (BMI = 18.5 – 24.9), the risk of premature death went up. Those in the overweight category (BMI = 25 – 29.9) had a 13 percent higher risk compared to those with a BMI of 22.5 – 24.9. Those in the obese category (BMI = 30 – 34.9) had a 44 percent higher risk. While those in the super obese categories with a BMI between 35 – 39.9 and 40 – 49.9 had an 88 percent increase and more than double the risk, respectively. (BMI Calculator).
As found in some other studies, there was also some increase in risk for those who fell in the underweight category (BMI = 15 – 18.4) and in the lower end of the normal range (BMI = 18.5 – 19.9). The data suggest though, that these numbers may be capturing some residual health issues, possibly undiagnosed illness which causes some of this increase in risk among the very lean. Those participants in the underweight category who were regularly active – a marker for good health – had less of an increase in risk than those who weren’t active. That the risk linked to underweight largely went away after 15 years of follow-up is another indicator that pre-existing illness may be at work in the group.
Perhaps the most notable finding from the paper is a clear and sustained increase in mortality seen in folks who fall in the overweight category (BMI = 25 – 29.9). Some previous results from some big studies, such as Flegal et al, 2007, found no increase in mortality in this category, most likely because they did not exclude smokers and those with illness as the current paper did.
What this new analysis clearly shows is that maintaining a healthy weight has real health benefits. While there will always be news stories and select journal articles calling into question the true benefits of a healthy weight, this paper shows that in the face of our growing obesity epidemic, where 66 percent of the US population is overweight or obese and therefore at increase risk of pre-mature death, we need to put to rest the question of whether overweight impacts health and start to answer in ernest the question: what are we going to do about it?