Man Flu, scourge of modern Manly life. Struck down by this dreaded disease men are reduced to a shadow of their former glory, unable to maintain the meager level of household responsibility they usually get away with or even care for their own well being. Reduced to mewling invalids, men afflicted with Man Flu have little recourse beyond bed rest and watching daytime television while a significant other tends to their every need. After being ridiculed by wives and girlfriends for decades science has come to the rescue and vindicated us, the Man Flu exists!*
*The preceding is a work of fiction and any resemblance to real people or events is coincidental.
Despite what the media would have us believe recent advances in scientific research has not in fact established that Man Flu is a real phenomena beyond simply showing our inability to deal with sickness effectively. The real science behind the hype, as usual, is much more modest in it’s scope and consequences.

So what was actually studied? The research was carried out by McGill University in Canada and looked at the effects of a certain protein, caspase-12. The study involved investigating how the activity of this protein affects immune response against Listeria monocytogenes bacteria, a microbe that can cause serious food poisoning, in mice. Part of the study also investigated the effect of gender on the activity of the protien and whether any difference was mediated by the hormone oestrogen. To do this researchers infected mice with the bacteria and looked at spleen and liver bacteria levels in male and female mice with and without the gene for the protein and male mice with the gene and being treated with estrogen. 

The interesting thing is that this gene did have a different effect on how sick the mice got depending on the presence or absence of estrogen. Those male mice with the gene were more susceptible to the infection than females or males recieving hormone treatment, but the gene is inactive in most humans. Only about 20% of native Africans have a working version of the gene, so this research has virtually no applicability to general differences in flu severity between men and women. I guess Man Flu remains a myth, for now.