During adulthood, our bodies tightly regulate the number of fat cells, which could explain why it seems easy to gain back lost weight.
Children exposed to a particular strain of a common cold virus are more likely to be obese than those not exposed, a new study suggests.
In a study of 124 children, ages 8 to 18, nearly 80 percent of those who had been exposed to a virus called adenovirus 36 were obese. They weighed an average of 50 pounds (23 kilograms) more than kids who were not exposed to the virus, said study researcher Dr. Jeffrey B. Schwimmer, associate professor of clinical pediatrics at the University of California, San Diego.
And among kids who were obese, those exposed to the virus weighed an average of 35 pounds (16 kg) more than obese kids who hadn't been exposed to the virus, he said.
"The bottom line is, it's a big number," Schwimmer told MyHealthNewsDaily. "Certainly, it's more than enough to be associated with health problems."
Thirty-five to 50 extra pounds is a lot for a child, considering an average, healthy 8-year-old usually weighs between 50 pounds and 90 pounds (23 kg to 41 kg) to begin with, Schwimmer said.
There are more than 50 strains of the adenovirus, which is the virus most commonly responsible for respiratory illnesses that range from the common cold to pneumonia-like sicknesses. Most people are exposed to some strain of the virus before age 10, according to the Nemours Center for Children's Health Media.
Scientists determined whether children had been exposed to the adenovirus by looking for antibodies in their blood.
The virus may affect obesity by infecting "pre-fat" cells – cells that have the ability to store fat – in the body and causing them to mature more quickly, Schwimmer said. It may also inhibit the cells' ability to break down fat, so fat cells become greater in both number and size.
"The more rapidly they become mature, the more fat cells a person will have," he said.
But that doesn't mean people should panic about being exposed to this strain of virus, he said. Even if the virus is a causal factor for obesity, not every person will have the same reaction to infection.
Childhood obesity has more than tripled over the last 30 years, according to the Centers for Disease Control and Prevention. Much attention has been paid to factors such as food intake, exercise, sedimentary lifestyles and genetics, but viral infection is another factor that should also be considered, Schwimmer said.
"Body weight regulation is complicated and differs from person to person," he said. "For some people, [exposure to the virus] may be a tremendously important factor, and less so for others."
Previous research has linked adenovirus strains to obesity in both animals and humans, but this study is the first to look at the role of the virus in childhood obesity, said Dr. Nikhil Dhurandhar, chief of the Infection and Obesity laboratory at the Pennington Biomedical Research Center in Louisiana, who has been studying what he calls "infectobesity" for the past 20 years.
"If there's at least some part of obesity that is caused by infections, then there is a potential to have a vaccine to prevent this type of obesity," said Dhurandhar, who is not involved with the study.
Researchers hope to learn whether children who are obese and were exposed to the virus respond to weight-loss methods differently than children who were never exposed the virus. They also hope to investigate the possibility of preventing the virus with a vaccine, and, if so, explore how to determine who should get it.
The study was published online Sept. 20 in the journal Pediatrics.
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