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Can a virus ever make you fat?

Ami Banerjee
Last edited 24th September 2010

On both sides of the Atlantic, obesity, particularly in childhood, is a growing problem (no pun intended). So earlier this week, when new research claimed to associate a virus that causes the “common cold” with the development of obesity, the media took interest in both the UK and the US.

Jeffrey Schwimmer, lead researcher was quoted on the BBC:
"It is time that we move away from assigning blame in favour of developing a level of understanding that will better support efforts at both prevention and treatment. These data add credence to the concept that an infection can be a cause or contributor to obesity.”

That is big chat. Like all papers published in major journals, the abstract or summary of the paper is available on PubMed for free. I used the abstract to examine these claims a bit further.

The authors set out to compare blood levels of antibodies to adenovirus (AD36) in children who were obese versus those who were not. The first problem is that they did a “cross-sectional study”, which means they took a snapshot of their patients at a single point in time, rather than following them up over a length of time. That means that we deduce nothing about the virus (the “exposure”) causing obesity (the “outcome”) since we are not following the children up over time from the onset of the infection of the virus. At best, we can talk about an association or a link. Secondly, they have kids from 8-18 years of age. Children at eight are very different to children at eighteen and so you might expect the effect of infection at different stages of childhood to be different. So why are they lumping all kids of all ages together?

In the results, only 124 children were studied, and we have no idea how many patients were excluded from original recruitment. Half of the 124 children were obese. Before we go any further, the antibody (AD36) was present in 15% of the children. In other words, any comments made about the relationship between the antibody and obesity is based on 19 children. That does not seem a big enough number to be making any claims.

The paper’s main findings are: “The majority of children found to be AD36-positive were obese (15 [78%] of 19 children). AD36 positivity was significantly (P _ .05) more frequent in obese children (15 [22%] of 67 children) than nonobese children (4 [7%] of 57 children)”. Again, we are looking at only 19 children who had viral antibodies. In addition, the p-value is only just statistically significant (p=0.05). You do not have to read the whole paper to see the limitations of research. Bottom line: regular Big Macs and lack of exercise are still much more likely to cause obesity in childhood than the common cold.

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