Is A Cold Virus Obesity’s Missing Link?

by Melissa Clark Vickers
October 27, 2010

With nearly one-third of U.S. children ages 2-19 overweight or obese, heaps  of research and media attention is targeting the causes of obesity. A highly improbable piece of the obesity puzzle was recently identified in the form of a cold virus. A recent study in Pediatrics investigated a possible association between a specific cold virus, adenovirus 36 (AD36), and childhood obesity—one that could account for as much as a 50-pound difference between children exposed to the virus and those not. “Association” is a long way from explicit “cause and effect,” but the study raises some intriguing questions.

Research
Adenovirus 36 (AD36) is no stranger to obesity. Previous studies have linked this common cold virus to obesity in adults—30 percent of obese adults have AD36 antibodies, while only 11 percent of non-obese adults have them. Building on these results, including a recent Korean study looking at the prevalence of AD36 in obese children, researchers from California explored the relationship between AD36-specific antibodies and obesity in children.

The study included a racially and ethnically diverse sample of 124 children ages 8-18 years old from San Diego, California. Children who had acute or chronic diseases affecting weight, genetic conditions associated with obesity, failure to thrive, and/or were taking medications known to cause weight gain or loss were excluded from the study.

The 124 children were grouped according to body mass index (BMI): obese (>95^th percentile) or nonobese (<95^th percentile). Fifty-four percent were classified as obese and 46 percent nonobese. In addition to height and weight, researchers measured waist and hip circumference, and the presence of AD36-specific neutralizing antibodies in their blood.

Results
Children exposed to the AD36 virus were significantly more likely to be obese than those not exposed:

• Fifteen of the 67 obese children (22 percent) tested positive for the AD36-specific antibodies, while only four of the 57 nonobese children tested positive.
• The average BMI for AD36-positive children (33.7) was significantly higher than AD36-negative children (26.8).
• Within the obese subgroup, the average BMI for AD36-positive children (36.6) was significantly higher than AD36-negative children (31.8).
• AD36-positive children weighed 52 pounds more than AD36-negative children.
• Within the obese subgroup, AD36-positive children weighed 35 pounds more than obese AD36-negative children.
• Waist and hip measurements were higher for the AD36-positive group as well.

While the differences between the groups are statistically significant, the study does have some considerable limitations. The sample size (124 children) is fairly small from which to make generalizations. In addition, this study did not attempt to look at family history to provide insight on how genetics might have played a role. Neither did researchers collect data on when the obese children gained the excess weight relative to cold infections, or even when the exposure to the AD36 virus might have occurred. The study also did not distinguish between “nonobese” and overweight children, with BMIs between the 85^th and 95^th percentile.

Recommendations
This study represents a significant departure from traditional thinking about causes of obesity (too many calories and not enough exercise). Studies with other primates, rats, and chickens have demonstrated that infecting these animals with the AD36 virus causes an increase in total body fat, independent of caloric intake. Studies with rats indicate that the virus can impact fatty acid and glucose metabolism, an effect also seen in human cells that suggests that they behave similarly to rodents infected with the virus.

Maybe we’re looking at this backwards. Instead of the virus causing obesity, perhaps obesity predisposes a child to be more susceptible to the virus in the first place. In a Letter to the Editor in response to this study, a North Carolina pediatrician suggests another possibility—Vitamin D deficiency:

“A far simpler and more probable explanation for the observed association lies in the fact that obesity is known to be associated with substantially increased risk of being vitamin D deficient–and a number of studies have shown that raising vitamin D levels is protective against susceptibility to colds and influenza.”

If the Adenovirus 36 virus is definitively shown to cause weight gain, it would have important treatment implications. A child who is obese by virtue of this cold virus might require a different treatment than one who is obese because of genes or a sedentary lifestyle.

The AD36 virus is one of many that cause cold-like symptoms, so practicing good hygiene (frequent hand-washing, covering the mouth when sneezing), especially during cold and flu season, is a common-sense approach to avoiding infection. There is currently no test for AD36, so taking the more prudent approach to a healthy lifestyle (eating sensibly and making physical activity routine for the entire family) is good insurance against those unwanted—and unhealthy—pounds.

Just as not every child who leads a sedentary lifestyle and eats too much junk food becomes overweight, not everyone exposed to the AD36 virus is doomed to obesity. Many pieces of the obesity puzzle have yet to be identified—or are not yet fully understood. As more attention is given to the obesity epidemic, we’re likely to see more of the pieces fall into place.