July 7, 2014
Tapan Mehta, PhD, assistant professor in the Department of Physical Therapy—in collaboration with Kevin R. Fontaine, PhD, professor and vice chair in the Department of Health Behavior; and Gustavo de los Campos, PhD, assistant professor, Alfred A. Bartolucci, PhD, professor emeritus, and David B. Allison, PhD, distinguished professor, in the Department of Biostatistics—evaluated whether the obesity-associated years of life lost (YLL) have decreased over calendar time.
There has been a debate over whether the harmful association of obesity on mortality has reduced over time due to conflicting results from individual analyses. Previous analyses of the National Health and Nutrition Examination Surveys suggested that the harmful association of obesity-mortality may have decreased over calendar time, while some other studies suggested that this might not be the case. Apart from the inconsistent findings, previous studies have been confounded by factors such as length of follow-up, recency of BMI measurement, age-related effect modification, and stable study level-factors. Dr. Mehta and colleagues collected individual-level data from multiple U.S. prospective studies that spanned different calendar times and mortality follow-up periods. They implemented a rigorous design and conducted analysis that adjusted for the aforementioned confounders.
Study findings show that the lifespan shortening association of obesity has reduced over calendar time in many groups. Grade 1 obesity’s (body mass index [BMI] 30 to less than 35) association with YLL has lessened over calendar time for older Caucasian men (ages over 60) but not for younger middle aged men (ages equal to or less than 60). In contrast for Caucasian women, there is evidence of a decline in the obesity-YLL association, both for Grade 1 obesity and Grades 2-3 obesity (BMI equal to or greater than 35), with reduced longevity across all adult ages.