New research from the US appears to back the suggestion that obesity may be triggered by a virus infection: it found that children had a higher chance of developing obesity if they had been exposed to a particular type of adenovirus.

The study was the work of researchers from the University of California (UC), San Diego School of Medicine and appears in the 20 September early online issue of the journal Pediatrics.

As a September publication, the study paper coincides with National Childhood Obesity Awareness Month.

One of the study investigators was Dr Jeffrey B Schwimmer, who is an associate professor of clinical pediatrics at UC San Diego, and also director of Weight and Wellness at Rady Children’s Hospital in San Diego. He told the press that he hopes this research will prevent obese people, and children in particular, from being blamed for their condition: we need to move away from “assigning blame in favor of developing a level of understanding that will better support efforts at both prevention and treatment”, he said.

“These data add credence to the concept that an infection can be a cause or contributor to obesity,” he added.

For the study Schwimmer and colleagues looked for evidence in a group of children of having been infected by a virus called adenovirus 36 or AD36.

The presence of neutralizing antibodies against AD36 shows that a child has been infected with the virus, which is one of over 50 strains of adenovirus known to infect humans. AD36 causes various types of infection in humans, including respiratory, eye and gastro-intestinal.

AD36 is the only strain that has been linked to obesity in humans, and animal studies have also shown links to obesity. However, we don’t know very much about the mechanisms behind the link: for example does it affect everyone in the same way, and is the weight gain that follows infection caused by a change in people’s metabolism?

Schimmer explained that lab studies with cell cultures have shown that the virus infects immature fat cells and prompts them to develop more quickly and replicate in larger numbers than normal.

He said more work needs to be done to show if this is a mechanism for obesity.

For the study, Schwimmer and colleagues examined 124 children aged between 8 and 18 (median age 13.6 years), of whom 67 (just over half) were considered obese, using the BMI percentile system recommended by the US Centers for Disease Control and Prevention (CDC).

(The CDC recommends a system for screening for childhood obesity that compares a child’s BMI (body mass index: weight in kilos divided by the square of the height in metres) to a standard population of the same age and sex. If the child’s BMI is in the 95th percentile or higher, then he or she is considered obese.)

The researchers tested for the presence of AD36-specific neutralizing antibodies using serum neutralization assays.

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Their results showed that:

The researchers concluded that: “These data support an association of obesity and higher body weight with the presence of neutralizing antibodies to AD36 in children.” They pointed out that their study was only able to establish a link between AD36 and obesity; it did not show that the virus triggered a propensity to obesity. However, they wrote that: “If a cause-and-effect relationship is established, it would have considerable implications for the prevention and treatment of childhood obesity.” Schwimmer said that carrying extra weight is a major concern at any age, “but especially so for a child”. “Obesity can be a marker for future health problems like heart disease, liver disease and diabetes. An extra 35 to 50 pounds is more than enough to greatly increase those risks,” he added. In the US, it is estimated that around 17 per cent of children and teenagers are obese, and that a person who is obese in childhood has a 70 to 80 per cent chance of continuing to be obese into adulthood. Poor eating habits, lack of exercise, stress and depression, as well as a family history of obesity, socioeconomic status and ethnicity are thought to contribute to risk for childhood obesity. “Adenovirus 36 and Obesity in Children and Adolescents.” Charles Gabbert, Michael Donohue, John Arnold, and Jeffrey B. Schwimmer. Pediatrics, Published online 20 September 2010. DOI:10.1542/peds.2009-3362 Additional source: UC San Diego.