Can you “catch” obesity?
and World Science staff
There is a lot of good advice to help us avoid becoming fat, such as eat less and exercise. But here’s a surprising piece of advice from researchers: wash your hands.
There is growing evidence that some viruses may cause obesity, thus making obesity contagious, said Leah Whigham of the University of Wisconsin, Madison, lead researcher in a new study on the subject.
The idea isn’t new, but it has been controversial among scientists, Whigham said. “It makes people feel more comfortable to think that obesity stems from lack of control,” she remarked. “It’s a big mental leap to think you can catch obesity.”
Her study found that a human-infecting virus called AD-37 causes obesity in chickens. Previous studies had found two three related viruses was associated with obesity in animals or humans, the researchers added.
The study appears in the January issue of the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology.
AD-37 and its kin are adenoviruses, members of a family of viruses that commonly cause upper respiratory tract infections including the common cold.
Whigham said more research is needed to find out if Ad-37 causes obesity in humans. One study was inconclusive, she said, because only a handful of people showed evidence of infection with Ad-37, not enough people to draw any conclusions.
Researchers should now identify which, if any, viruses cause human obesity, she added. Fruther steps could be to devise a screening test to identify people who are infected; and develop a vaccine.
“If Ad-36 is responsible for a significant portion of human obesity, the logical therapeutic intervention would be to develop a vaccine to prevent future infections,” wrote Frank Greenway of Louisiana State University, Baton Rouge, in an editorial in the same issue of the journal. “One would want to ensure that all the [subtypes] of human adenoviruses responsible for human obesity were covered in the vaccine.”
The notion that viruses can cause obesity isn’t new, but it has been controversial among scientists, Whigham said.
Yet, there is evidence that factors other than poor diet or lack of exercise may be at work in the obesity epidemic. “The prevalence of obesity has doubled in adults in the United States in the last 30 years and has tripled in children,” the study noted. “With the exception of infectious diseases, no other chronic disease in history has spread so rapidly,” and the causes have not been clearly identified, she added.
Other diseases once thought to be the product of environmental factors are now known to stem from pathogens, she added. For example, ulcers were once thought to be the result of stress, but researchers eventually implicated bacteria, H. pylori, as a cause.
“The nearly simultaneous increase in the prevalence of obesity in most countries of the world is difficult to explain by changes in food intake and exercise alone, and suggest that adenoviruses could have contributed,” the study said. “The role of adenoviruses in the worldwide epidemic of obesity is a critical question that demands additional research.”
The theory that viruses could play a part in obesity began a few decades ago, the researchers said. That was when Nikhil Dhurandhar, now at Louisiana State University, noticed that chickens in India infected with the avian adenovirus SMAM-1 had significantly more fat than non-infected chickens.
The discovery was intriguing because the explosion of human obesity, even in poor countries, has led to suspicions that overeating and lack of exercise weren’t the only culprits in the rapidly widening human girth. Since then, Ad-36 has been found to be more prevalent in obese humans, Whigham and colleagues noted.
In the new study, the team worked to determine which adenoviruses might be associated with obesity in chickens. The animals were separated into four groups, each of which was exposed to one of three adenoviruses, or no virus.
Chickens inoculated with Ad-37 had significantly more fat compared with the other three groups, which included those infected with Ad-2 or Ad-31, the researchers found. The authors concluded that Ad-37 increases obesity in chickens.
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