Obese kids and AD-36: Is obesity caused by a virus?

© 2010 Gwen Dewar, all rights reserved

If so, there is hope. Because researchers are testing a new vaccine against adenovirus-36.

Obesity rates among children are skyrocketing, and it’s clear that many factors are involved.

Kids might eat more and exercise less. They might also gain weight because they don’t sleep enough at night.

But what about contagion? Is it possible that some kids are getting fatter because they’ve been infected with a virus?

The concept has been dubbed “infectobesity” (Dhurandhar 2001) and it would have been dismissed as outlandish decades ago.

But in recent years, researchers have discovered evidence that viruses contribute to all sorts of chronic medical conditions (Ewald 2002). Now they are adding obesity to the list. And the culprit of interest is adenovirus-36, also known as AD-36.

AD-36 is one of many viruses that cause the common cold. But unlike other strains, AD-36 has an alarming side effect. Add it to a Petri dish of human stem cells, and those cells begin making fat cells. Lots of fat cells.

The virus appears to speed up the rate at which fat cells develop. And it may make fat cells grow larger, too.

Does this mean that human beings who are exposed to the virus will get fatter?

The classic way to answer such a question is with a randomized, double-blind study. Inject some people with adenovirus-36, and other people with saline solution. Follow up with years of observation and see who gets fatter.

• In experiments on chickens, rodents, and monkeys, the animals exposed to adenovirus-36 got fatter—in some cases packing on more than 4 times as much weight as did controls (Atkinson 2007; Dhurandhar et al 2002).

• In clinical studies on human beings, researchers have found that obese people are more likely to test positive for adenovirus-36 antibodies—evidence that they had been exposed to the virus in the past (Atkinson 2007).

And obese kids?

Sixty-seven kids were obese, 57 were of normal weight. Of the obese kids, 15 tested positive for antibodies. Only 4 of the slim kids tested positive.

So obese kids were more likely to have been exposed to AD. And that’s not all. Among the obese kids, the fattest were those who’d tested positive for antibodies.

Principal investigator Jeffrey B. Schwimmer explains in a press release video clip:

“When we looked only at obese children, those obese children with evidence of infection by adenovirus-36 weighed on average 35 pounds more than did obese children who did not have evidence of infection with this virus.”

It's an interesting point, particularly considering the alternative hypothesis--that obese kids are more likely to get infected with AD-36 because they have poorer immune systems.

If this were the case, it's not clear why obese children who have been exposed to AD-36 would be heavier than obese children who have not been exposed.

Unanswered questions

Maybe they were exposed only recently and the effects haven’t yet emerged. But it’s also possible that the virus affects some people differently, or that some infections are more severe than others. And of course some people may work especially hard to fight the accumulation of fat. More research is needed.

But the case for infectobesity remains compelling. And the timing seems right. As Richard Atkinson notes, the virus was first discovered by researchers in 1978, just before the worldwide epidemic of obesity took off (Atkinson 2007).

Moreover, adenovirus-36 isn’t the only virus associated with obesity in humans. Researchers in India found that obese people who tested positive for antibodies to the SMAM-1 virus were significantly heavier than obese people who tested negative (Dhurandhar et al 1997). More such viruses may be identified in the future.

Can we do anything about infectobesity?

But researchers are testing a new vaccine against adenovirus-36. In a few years, it may come on the market. An “obesity vaccine” may become a regular part of pediatric visits.

Until then, nervous skinny people should note that this research doesn’t justify putting obese people in quarantine.

Adenovirus-36 is a cold virus, so people are contagious when they are suffering from the cold symptoms--not months later when they’ve begun to gain weight. As Jeffrey Schwimmer tells Science News, “It’s the skinny person with a cold you have to watch out for."

And perhaps we shouldn’t resent this virus too much. In many--but not all--studies, AD-36 is also linked with lower cholesterol levels (Atkinson et al 2007; Na et al 2009). And for most of human history, people were mostly concerned with getting enough to eat. A virus that helped your body store fat would have been a good thing.

Is AD-36 one of the first human viruses known to benefit people—at least under certain conditions? I wonder. As reader Simon Waters has reminded me, there are the viruses that benefit us indirectly, by making us immune to other, closely related pathogens. But are there any other viruses that have more direct effects? I look forward to finding out.

References: Obese kids and AD-36

Dhurandhar NV. 2001. Infectobesity: Obesity of Infectious Origin. Journal of Nutrition 131:2794S-2797S.

Dhurandhar NV, Kulkarni PR, Ajinkya SM, Sherikar AA, and Atkinson RL.1997. Association of adenovirus infection with human obesity. Obes Res. 1997 Sep;5(5):464-9.

Ewald PW. 2002. Plague Time: The New Germ Theory of Disease. New York: Anchor Press.

Gabbert C, Donahue M, Arold J, and Schwimmer JB. 2010. Adenovirus 36 and Obesity in Children and Adolescents. Pediatrics. Published online September 20, 2010 (doi:10.1542/peds.2009-3362).

Na HN, Hong YM, Kim J, Kim HK, Jo I, and Nam JH. 2009. Association between human adenovirus-36 and lipid disorders in Korean schoolchildren. Int J Obes (Lond). 2010 Jan;34(1):89-93.

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