Men across the world who complain of sickness and are dismissed as having "man flu" have been vindicated by a new study which has found that female hormones actually protect women against the influenza virus.

The study published on Wednesday in the American Journal of Physiology - Lung Cellular and Molecular Physiology, found that the female sex hormone estrogen has antiviral effects against the influenza A virus.

Man flu ... it's real.

The team of researchers from John Hopkins University found that the antiviral properties of estrogen could protect women from the more aggressive symptoms of the virus, and may even be able to be harnessed to treat infections more broadly.

The findings support the idea that men are more vulnerable to the flu and may experience more severe symptoms of the illness, lead researcher Dr Sabra Klein said.