A virus that can cause obesity in animals may be linked to some cases of obesity in humans, researchers at the University of Wisconsin Medical School have found.
A preliminary study of 199 people has shown that as many as 15 percent of obese people may carry antibodies to the virus, indirect evidence that they once were exposed to the virus itself. None of the lean volunteers tested had the antibodies.
Dr. Nikhil Dhurandhar described the findings Mon., April 7, at the Experimental Biology annual meeting in New Orleans. An assistant research scientist in the UW Medical School department of medicine, Dhurandhar conducted the research with UW Medical School Professor of Medicine and Nutritional Sciences Dr. Richard Atkinson.
Between 80 and 90 million Americans are obese, defined as having a body-mass index of 27 or above. Body mass index is calculated by dividing a person's weight in kilograms by the square of height in meters. A viral connection to obesity in humans has never been seriously considered before, the researchers noted.
Dhurandhar first found that one type of adenovirus that infects birds and is found only in his native India could induce obesity when it was injected into chickens.
Human adenoviruses form a large family of some 50 viruses. Transmitted through the air, they can cause upper respiratory infections, cold symptoms, gastrointestinal problems and eye inflammation in humans.
Dhurandhar and Atkinson next injected laboratory animals with a form of adenovirus known to affect humans, Ad-36, which resulted in obesity.
"A paradoxical characteristic of the virus is that in animals it appears to produce low levels of cholesterol and triglycerides along with the obesity," said Dhurandhar, noting that obesity is usually accompanied by elevated levels of these substances.
In the current study, Dhurandhar tested 154 obese and 45 lean human volunteers for the presence of antibodies to Ad-36. He found about 15 percent of the obese volunteers had antibodies to Ad-36 while the lean volunteers showed none.
The antibody-positive obese people had significantly lower cholesterol and triglycerides levels than the antibody-negative obese people, a pattern similar to that seen in animals infected with Ad-36. But the two groups did not differ on any of 29 other measures the researchers compared, including age or family history of obesity.
In males the presence of antibodies was associated with a significantly better response to treatment with obesity drugs, said Dhurandhar.
"There has been an alarming worldwide increase in the prevalence of obesity in the past 30 years," said Atkinson, noting that its prevalence in the United States rose 30 percent between 1980 and 1990, affecting more than 33 percent of the population. "This increase is the type of pattern that might occur with a new infectious disease, as has been seen with the AIDS virus. A great deal of further research is necessary to determine if the global epidemic of obesity may be due in part to infection with Ad-36."
The research was funded in part by the UW Beers-Murphy Clinical Nutrition Center.