Is Child Obesity an Infectious Disease?

A commentary on the link between a cold virus and obesity.

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Is obesity contagious? The surprising news that some obese children are more apt to carry a common cold virus than slimmer children has many people wondering. If the potential link between the adenovirus 36 and childhood obesity turns out to be real, then someday new obesity treatments might be tailored to attack the virus to treat or prevent childhood obesity, an epidemic that affects 17 percent of American children and teenagers.

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There have been other unexpected discoveries of microbes causing disease, the most famous being the bacterium Heliobactor pylori, which turned out to be the major cause of stomach ulcers. In the early 20th century, ulcers were thought to be caused by stress and excess stomach acid, and sufferers were told to rest and eat bland food. In 1982, when two Australian physicians first said H. pylori caused ulcers, the international medical community scoffed. It took more than a decade for that fact to be accepted as true. An H. pylori test and antibiotics are now the recommended treatment for ulcers.

The new report on child obesity and viruses, published in Pediatrics, found that children who had been exposed to the adenovirus 36 were more likely to be obese than children who were never infected, with 22 percent of obese children having antibodies to the virus, compared to 7 percent of normal-weight children. The antibodies indicate that the body's immune system has tried to defend itself against the virus, a sign of prior exposure or infection. The study tested 67 obese and 57 normal-weight children, and was led by researchers at the University of California-San Diego and Rady Children's Hospital. Other studies in adults have found that obese folks are also more likely to have antibodies to the virus than are slimmer people.

However, 4 of the 19 children in the new study who carried antibodies were not overweight, so the association between infection and weight is far from proven. That's true in adults, too. And the majority of the obese children in the study hadn't been exposed to adenovirus 36, yet they were still fat. So the "obesity is an infection" theory doesn't let anyone abandon a healthy diet and exercise in favor of antiviral medications—at least not yet.

Even if the link between the virus and obesity is proven, weight gain remains a complex issue that involves a person's genetics, culture, and environment, not just his or her history of infection. Indeed, people are more likely to become obese if their friends are overweight, a 2007 study in the New England Journal of Medicine found. People became heavier if someone close to them gained weight, with men being 44 percent more likely to become obese if their brother put on weight, and women being 67 percent more likely if their sister gained weight.

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If adenovirus 36 turns out to be the culprit behind some obesity cases, new treatments might make the painfully difficult task of losing weight a bit easier for some. But most of us, children and adults alike, will still have to follow the weight-control advice we often don't like to hear: eat healthy, watch portion sizes, and get outside and play for an hour a day.

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