Obesity linked to virus, new experiments suggest
July 28, 2000
Web posted at: 2:35 PM EDT (1835 GMT)
(AP) -- A cold-like virus may cause obesity, new experiments suggest.
Researchers at the University of Wisconsin in Madison have found that mice and chickens infected with a common human virus put on much more fat than uninfected animals. They have also discovered that the same virus is more prevalent among overweight people, a strong indication that it may also cause obesity in humans.
In four experiments, the Wisconsin researchers inoculated chickens and mice with adenovirus-36, a member of a viral family that includes about 50 strains. Most adenoviruses cause colds, diarrhea or pinkeye.
After several months, animals infected with adenovirus-36 weighed only 7 percent more on average than those without the virus, but their bodies contained more than twice as much fat.
"This is the first human virus that has been shown to cause obesity in animals," said Nikhil Dhurandhar, one of the study's authors.
It is also the first virus the researchers looked at, raising the possibility that other human viruses may also cause obesity. Dhurandhar and his colleagues picked adenovirus-36 simply because little is known about it and the strain is relatively easy to work with.
Their study is being published in the August issue of the International Journal of Obesity.
"It raises a host of very interesting questions," said John Foreyt, an obesity expert at Baylor College of Medicine. "If it really does play a role I think it's a real breakthrough."
The latest results do not indicate that all obesity is caused by viruses, Foreyt said. But they strongly suggest that infection plays an important role.
"There's just so much more we need to do on this before we can say anything definitive," said Richard Atkinson, a University of Wisconsin professor and author of the study.
Unpublished studies in humans show that 20 to 30 percent of overweight people are infected with adenovirus-36, compared to about 5 percent of the lean population.
Experts are not completely surprised by the Wisconsin group's results. In the last few years, they have found signs that many chronic health conditions are caused by infections. Three different microbes are thought to contribute to clogged arteries. Long thought to be a product of high stress and a poor diet, ulcers are now known to be caused by the bacterium Helicobacter pylori.
In addition, several animal viruses are already known to cause obesity in both animals and humans. But adenovirus-36 is the first human virus known to cause an increase in fat.
Researchers do not know yet how adenovirus-36 causes obesity. Infected animals did not eat more than uninfected ones, suggesting that the virus decreases energy expenditure rather than increasing appetite.
"I feel that it increases the number of fat cells, which encourages them to store more fat," said Dhurandhar, who recently joined Wayne State University in Detroit.
The animal obesity viruses appear to work differently from adenovirus-36, by damaging the part of the brain that controls appetite. The Wisconsin researchers saw no brain damage in chickens and mice infected with adenovirus-36.
Aside from a day or two of cold-like symptoms, Atkinson said, the virus produced no observable effects besides obesity.
Paradoxically, animals infected with the virus also had decreased levels of cholesterol and triglycerides in their blood. Generally, obesity is associated with high cholesterol and triglyceride levels.
Far more research is needed before any practical benefits can be reaped from this research, Atkinson said. It is still too early to know whether it may be possible to develop an effective vaccine against obesity or otherwise counteract the effects of the virus.
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