June 26, 2006

BIRMINGHAM, Ala. – Poor diet and lack of exercise are well-known causes of obesity. But what about the amount of sleep a person receives, or even exposure to air conditioning? These may be just as important, according to an article published today in the International Journal of Obesity.

David B. Allison, Ph.D., professor of biostatistics in the University of Alabama at Birmingham (UAB) School of Public Health, and colleagues, reviewed several studies on food marketing practices and institutionally driven reductions in physical activity and their impact on increases in obesity rates. They found that the data are far from conclusive. They also reviewed data regarding other presumed causes of obesity that are less often considered but also provide compelling data. These factors included the average hours of sleep that persons receive, the use of psychotropic medications and how much someone uses air conditioning and heating.

“Obesity has increased across the board, and changes in age, race, sex, and smoking status of the population cannot completely account for the epidemic,” Allison said “This paper introduces 10 hypotheses regarding factors that may have contributed to the rise of the obesity epidemic and suggests the need for a more broad-reaching and open-minded inquiry on putatively contributing factors. We believe addressing some of these factors could have implications for both the treatment and prevention of obesity.”

The 10 factors that may have contributed to the rise in obesity rates are:

• Less sleep can cause increased body weight;
  
  
• Endocrine disruptors, including DDT and PCBs can increase body fat;
  
  
• Keeping ones home or office at one temperature year around promotes body fat;
  
  
• Smoking cessation increases weight because nicotine has both thermogenic and appetite suppressant effects;
  
  
• Certain pharmaceuticals, including antipsychotics, antidepressants, contraceptives and antihistamines increase weight;
  
  
• Some age and ethnic groups that have a higher prevalence of obesity than others have increased as a proportion of the population;
  
  
• Greater maternal age may increases risk of offspring obesity;
  
  
• Obesity may perpetuate its own increase through a fetally-driven positive feedback loop;
  
  
• Obesity has a genetic component and individuals with genetic predisposition toward obesity may be reproducing at a higher rate; and
  
  
• The probability that two individuals will mate is related to how similar their body types in adiposity and this can increase the number of offspring with high levels of adiposity.
  
  

“If these additional explanations are probable contributors to the obesity epidemic, as we believe they are, then additional research is warranted to evaluate how much they actually contribute, their mechanisms of action, their interaction effects and how they may be countermanded,” Allison said. “While we are not discounting the potential effects of food marketing practices and institutionally driven reductions in physical activity, if these other explanations are as veracious as we believe they might be, then the expectations for the likely public health impact of programs that only target the food marketing and physical activity might be tempered. Public health practitioners and clinicians may need to address a broader range of influential factors to more adequately address the epidemic.”