ADAPTIVE THERMOGENESIS AS AN EXPLANATION FOR THE GEOGRAPHIC
DISPARITIES IN CHILDHOOD OBESITY IN THE UNITED STATES
Kenneth J. McLeod, Craig Laramee, and Leann M. Lesperance
Program in Biomedical Engineering, Watson School of Engineering and Applied Sciences
Clinical Science and Engineering Research Center
Binghamton University, Binghamton, NY 13902
Contact Information: kmcleod@binghamton.edu
Background: The wide disparities in geographic prevalence rates for pediatric obesity (greater
than a factor of two) in the U.S. have served as a basis for investigating various factors which
may be contributing to the childhood obesity epidemic. While factors such as educational
attainment, poverty levels, and access to healthcare are commonly implicated in the rising levels
of obesity, body mass is strongly influenced by the physiologic requirement to maintain heat
balance (i.e. adaptive thermogenesis, and thus, changes in the modern living environment may be
significantly influencing obesity rates as well. We hypothesized that sustained exposure of
children to chilled and/or dehumidified environments, which are sufficient to cause high body
heat losses may explain a substantial fraction of the geographic disparities in pediatric obesity
rates.
Methods: We undertook a correlation analysis between childhood obesity prevalence and
surrogates of air-conditioning exposure in each state (cooling-degree-days and relative
humidity), and included three additional factors commonly associated with health outcomes:
general practitioners per 100,000, high school graduation rates, and childhood poverty levels.
Least squares linear regression was used in all analyses with parameters mean centered for all
regression involving interaction terms. The fraction of the various states’ population born in their
state of residency varies from a low of 21% in Nevada to 79% in Louisiana. Because low nativeborn residency rates admit the possibility that obesity prevalence in the affected states may not
reflect a long term adaptation to the built environment, analyses were weighted by native-born
residency.
Results: Prevalence of obese school-aged children in the contiguous 48 states ranges from a low
of 13% in Colorado to a high of 28% in Mississippi. Population-weighted cooling-degree-days
for the 48 contiguous states range from under 250 oF-days in Oregon to more than 3460 oF-days
in Florida; relative humidity ranges from 23% (Arizona) to 65% (Wisconsin); fraction of
children living in poverty ranges from 6.5% (New Hampshire) to 32.8% (Mississippi); high
school graduation rates range from 60.1% (South Carolina) to 87.8% (Nebraska); and primary
care physician density ranges from 78.9 per 100,000 (Idaho) to 189 per 100,000 (Massachusetts).
Least squares linear regression analysis identified only childhood poverty levels and the two
environmental factors as significant predictors of childhood obesity prevalence, and these latter
two factors are sufficient to explain over 80% of the obesity prevalence variation in the U.S.
Conclusions: Adaptive thermogenesis resulting from chronic exposure to chilled environments
appears to play a significant role in the development of childhood obesity in the U.S. This
observation may provide insight for developing new approaches for addressing the increasing
prevalence of childhood obesity both in the U.S. as well as other developed and developing
countries.
Keywords: Childhood obesity, physiologic adaptation, built environment