Harvard Men's Health Watch

On call: An obesity virus?

Q. I was very interested in your article on how obesity seems to spread through social networks. I understand that it's a new type of research, but I wonder if it might have overlooked the possibility that obesity might also be spread by an actual virus.

A. Obesity in America has increased steadily since 1960, with a particularly dramatic increase between 1980 and 2010. Because genetic changes cannot explain the obesity epidemic, scientists have considered other causes. At least five animal viruses can cause obesity, but these infections cause many serious, often fatal abnormalities in addition to excess body fat. Only one human virus, adenovirus 36, has been linked to obesity in people, but the link is indirect: individuals with evidence of previous adenovirus 36 infection are more likely to be obese than people who have never been infected. But even if it's confirmed, this type of research can establish an association but not a cause-and-effect relationship between the virus and obesity.

It's an interesting observation that warrants more research. Still, it's a mistake to blame our expanding national waistline on viruses or even on the way obesity-prone behavior can spread through social networks. Instead, think about the calories we consume and the hours we spend glued to video screens.

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