Is the Man Flu a Reality?

We all get sick. Young or old, male or female, everyone gets sick at some point in their lives. But only some are susceptible to a specialized disease known as the "Man Flu," which somehow causes men to think they have the flu when, in fact, they have only a little cold.

Where did the idea of a Man Flu come from? It's origins are uncertain. In general, a lot of people tend to think they're worse off than they really are when they're sick - a poll by Panadol Cold and Flu, for example, found that 61% of people who went to pharmacists claiming to have the flu didn't. Somewhere along the line, anecdotal evidence began to suggest that when men get sick, they whine more, think they are sicker than they are, and generally make more of a fuss than women. How this became a pop-culture norm isn't certain, but in 2006 a non-scientific survey stirred up the controversy by claiming that the Man Flu was real. The web-based survey found that men are more likely to skip work when they think they have the flu, even though they only have a cold. Furthermore, it found that men moan more, spend more on drugs, and stay in bed longer until they feel better. Men reported taking three days to recover on average, while it only took women a day and a half to feel better.

Of course, a web-based survey of magazine readers is hardly a reputable study. But it fired up the debate none the less, and now attention is focused on the real science behind the Man Flu. Do men really think they're sicker than they are? Do they exaggerate their illnesses? Or, even, do they get sick more often than women?

The media sure thinks the science is clear. In 2009, news outlets went nuts over a study that they claimed showed women have stronger immune systems. "Man Flu is Not A Myth," the Daily Mail touted. Furthermore, "scientists prove men suffer more from disease," thanks to the results of a new study published online this week.

Of course, trusting the media's interpretation of science is like handing your car keys over to a five year old. Here's what these studies really found:

In 2009, researchers from McGill University published a paper in the Proceedings of the National Academy of Sciences titled, "Gender differences in expression of the human caspase-12 long variant determines susceptibility to Listeria monocytogenes infection." While hailed by the media to prove that women resist the flu because have better immune systems than men, the study actually was looking into the effects of Caspase 12 on resistance to a particular bacterial infection in male and female mice.

Caspases are a kind of enzyme called proteases which are responsible for the breakdown of other proteins. They are often activated during inflammation, like when our bodies are fighting off illnesses. A particular mutated form of Caspase 12 has been implicated to be involved in the susceptibility to severe bacterial infections, and the researchers wanted to know how this mutated caspase might cause this. So they genetically modified mice to have different versions of the caspase, and intentionally gave them a bacterial infection. To their surprise, they found that the female mice that had the mutated caspase did better than the male mice, and further experiments found that estrogen levels were a key player in this protection against infection. Expression of estrogen actually lowered the expression levels of the mutant caspase, protecting the females against the bacterial assault.

While this study is fascinating and really, really cool, it says nothing about how men and women respond to the flu. First off, it's in mice. While mice are a great model for many diseases, they aren't perfect mirrors of human immune systems. We cure cancers in mice every day that we can't cure in people, for example. Rodent systems can give us clues to the underlying immune pathways, but they don't tell us exactly how people's cells behave. It certainly didn't, in any way shape or form, show that disease rates are higher in men than women, or that any group of humans suffers more from any disease in terms of frequency or severity.

Secondly, it studied the susceptibility to bacterial infections, not viral infections like influenza or the common cold. While our bodies may have some of the same reactions to the two, like fevers and sneezing, the immune response cascades are very different. So while the study did teach scientists more about how immune systems may respond to bacterial infections, it told us absolutely nothing about whether men are more likely to catch or feel worse from the flu.

What about the 2010 study, then?

Just this week, so-called "experts" were said to have found that the Man Flu is real. The study they're referring to is the newest publication out of Cambridge University, titled "The evolution of sex-specific immune defences," which is online first through the Proceedings of the Royal Society B. In it, authors Olivier Restif and William Amos detail the results of an adaptive dynamic model which takes into account both includes host-pathogen population dynamics and host sexual reproduction.

What they found was that reproductive differences alone were not enough to select for the evolution of different levels of immunity. However, when ecological factors added to the mix - say, for example, higher rates of exposure to disease in one population - different sexes could evolve different levels of suceptibility to disease. Specifically, they found that if men were more at risk of disease due to adventurous behavioral tendencies, they might develop lower immunocompetence over time than women.

These data are counterintuitive in many cases, and may indeed revolutionize the way researchers think about how the immune system evolves in response to ecological conditions. However, they don't tell us anything about our current immune system. Modeling is a great way to look at how a system may have changed or may change in the future, but it's not an exact science. The results in this paper don't say that men currently suffer from more illnesses, are more immunocompromised than women when given an infection, or that they are more likely to whine about it - instead, they simply suggest that there could have been reasons for such differences to evolve. That's all.

So does the Man Flu really exist? Wives will tell you it does. I know Barry can be a real baby when he gets sick. But as for any scientific evidence, the jury is still out. Until someone looks directly at how men and women react to viral infections, we don't have any valid evidence to suggest that the Man Flu is real.

Citations:
Yeretssian, G., Doiron, K., Shao, W., Leavitt, B., Hayden, M., Nicholson, D., & Saleh, M. (2009). Gender differences in expression of the human caspase-12 long variant determines susceptibility to Listeria monocytogenes infection Proceedings of the National Academy of Sciences, 106 (22), 9016-9020 DOI: 10.1073/pnas.0813362106

Restif, O., & Amos, W. (2010). The evolution of sex-specific immune defences Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2010.0188