As it's unethical to test these viruses in humans, for now all of the evidence for their effect on people comes from associative data. Previous work done by Dr. Dhurandhar and his colleagues showed that in a randomly tested population, 30 percent of obese people had been exposed to Ad-36 as compared to only five percent of lean people.
"We even have some twin data that indicates that if you have twins who are discordant for [Ad-36] — meaning one has been exposed to the virus and one hasn't — the twin who has been exposed to the virus and has antibodies to that virus is more obese than the twin," Whigham adds.
However, she says once the mechanism of the viruses is better understood, it will be possible to develop tests that more definitively determine whether the virus is causing obesity in humans. She says that all that can be said about the mechanism of the viruses at this point is that they work on a cellular level, turning on and off genes related to fat cell maturity. So, while it's not yet known how a virus could increase fat, some obesity researchers, like endocrinologist Frank Greenway at the Pennington Center at Louisiana State University, think they may be contributing to the obesity epidemic.
"When I first heard that obesity might be caused by a virus, I was quite surprised. As one now looks back at the increase in obesity, clearly it's rising very fast and it has to be something that's in the environment," Greenway says. "Now, I don't think that viruses are causing the whole problem, but they may well be part of it."
Whigham says infection with one of these viruses is likely not a guaranteed sentence to obesity. "At this point there's no reason to cause people to panic that if they get exposed to the virus they will definitely become fat. And I also remind people that there's lots of good reasons to follow a healthy diet and a regular exercise program," she adds.
Important next steps in this line of research will include determining how many of the other adenoviruses could be causing increased fat. Once they are all identified, it may be possible to start developing a vaccine. Till then, our best bet is to keep our hands clean.
Anyone who feels their exercise and dieting is failing for more than just the ordinary reasons can actually get tested — Obetech, LLC has developed a test for antibodies to Ad-36. The company was founded by Richard Atkinson, another of the main researchers in this field, and one of the authors on this study.
This research was published in the Januray, 2006 issue of the American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, and was funded by the National Institutes of Diabetes and Digestive and Kidney Diseases and the Beers-Murphy Clinical Nutrition Center, University of Wisconsin.