Health Spectator

In our editorial on the spread of obesity through social networks, Health Spectator mentioned that we doubted purely social causes were at work in the spread of obesity. We suggested that the network model discussed by Christakis and Fowler could result from an “infectious agent” that might possibly include a set of eating and exercise habits.

But it could also indicate a more typical infectious agent such as a virus or bacterium.

In fact, at least one study had already established that a virus occurring in humans—Ad-36, now the subject of much general press—could cause obesity in animals. And other researchers have become increasingly suspicious that not only obesity, but cancer, heart disease, and other major illnesses could result at least partially from infection by viruses or bacteria. Such evidence has been steadily mounting.

As we reported in our news story based on a paper just published in the International Journal of Obesity, Dr Richard L. Atkinson and other researchers tested both obese and thin volunteers for antibodies to adenovirus-36—the suspected agent—as well as three other viruses not believed to be linked to obesity. They not only searched for antibodies to the virus, but checked serum lipid levels (cholesterol and triglycerides) as well. They also measured the body mass index (BMI) of the individuals and their percentage body fat.

The researchers also included 89 pairs of twins in their study, enabling them to compare differences between twins who tested differently for exposure to Ad-36.

Years ago, animal experiments showed that when infected with Ad-36, stem cells turned into fat cells. It is well known that increasing the number of fat cells in the body enhances the likelihood that the individual will be overweight.

The present study was designed to test for an effect of the virus on humans.

When all the data were analyzed, the scientists found that 30% of the obese versus 11% of the thin subjects had been exposed to the adenovirus. Among twin pairs in which one twin had been exposed to the adenovirus and one had not, the exposed twins showed higher percentage body fat and BMI than their siblings.

Perhaps the most surprising effect of the adenovirus confirmed in this study is that while it increases fat accumulation, it lowers serum triglyceride and cholesterol levels.

As expected, the study showed no correlation between human obesity, cholesterol or triglyceride levels and exposure to the adenoviruses known as Ad-2, Ad-31, and Ad-37.