MedicalResearch.com Interview with:
Ching-Ti Liu, PhD
Department of Biostatistics
Boston University School of Public Health
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: Being overweight and obese are increasing worldwide and this obesity epidemic threatens to reverse the gains in life expectancy achieved over the past century. However, many investigators have observed, paradoxically, that overweight individuals are associated with a lower mortality risk. These results may suffer from a potential confounding due to illness or reverse causality in which preexisting conditions may alter both body weight and the risk of death. Recently published studies have tried to mitigate this reverse causal bias by implementing sample exclusion and they came to a different conclusion: between BMI and all-cause mortality there is an increased risk of death for the entire range of weights that are in the overweight and obesity ranges.
However, the elimination strategies may lead to the loss of generalizability or precision due to over-adjustment. In addition, the traditional investigations have only utilized a subject’s weight at a single point in time, which makes it difficult to adequately address bias associated with reverse causality.
Currently, the idea incorporating a subject’s weight history has been proposed to deal with the concern of reverse causality, but the existing works had been based on a subject’s recall or self-reported data, which may lead to misclassification and, therefore, result in overestimating the risk of mortality.
To help assess the relevance of being overweight or obese to the risk of death in the general population, we conducted a prospective study, using an individuals’ maximum BMI before the beginning of survival follow-up instead of their weight status at a single point in time, using data from the Framingham Heart Study (FHS).
We observed increasing risk of mortality across various BMI categories (overweight < obese I < obese II) relative to normal weight using maximum BMI over 24 years of weight history.
MedicalResearch.com: What should readers take away from your report?
Response: The implications from this study are as follows:
- First, the mortality risks associated with being overweight and obese are likely underestimated by conventional analytic approaches that rely on a snapshot of weight status for assessing risks. By incorporating the subjects’ weight history, the mortality risks increase substantially, implying that obesity may be a more serious threat to the health of individuals and populations than is currently understood;
- Second, there are also specific implications around our findings of elevated risks in the overweight category. This is a large group and, therefore, our finding of a positive association with risk in contrast to prior evidence which shows a negative association has implications for both clinical practice and population health impact;
- Third,, from a clinical perspective, our findings highlight the importance of eliciting information on weight history from patients for a comprehensive understanding of their health status; and finally, our results reinforce the importance of living a healthy lifestyle and maintaining a normal body weight.
MedicalResearch.com: What recommendations do you have for future research as a result of this work?
Response: The majority of our data sample were of white ethnicity, which limits the generalizability to other ethnicities/races. Therefore, it is worth investigating the pattern in other ethnicities/races as well. Additionally, incorporating the information on dieting that results in BMI changes or weight loss may help to elucidate the association further.
Disclosures: The article contains funding/support and conflict of interest disclosures. Please see the article for the information.
Xu H, Cupples LA, Stokes A, Liu C. Association of Obesity With Mortality Over 24 Years of Weight HistoryFindings From the Framingham Heart Study. JAMA Netw Open. 2018;1(7):e184587. doi:10.1001/jamanetworkopen.2018.4587
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