"Man flu" may not be the convenient myth promulgated by lazy blokes that its critics claim it is, according to findings by a team of scientists at an American university.
Their research has found that high testosterone levels may make men more susceptible than women to a range of ailments.
Researchers at Stanford University believe that their research may explain why men fall ill more often with a number of bacterial, viral, fungal and parasitic infections, and may also explain why immunisation drugs for flu, yellow fever, measles and hepatitis are less effective when administered to men.
In tests, scientists delivered a flu vaccine to 53 women and 34 men.
The jab caused a surge in protective antibodies in the women but in the men provoked responses that resulted in a decline in the number of antibodies.
"This is the first study to show an explicit correlation between testosterone levels, gene expression and immune responsiveness in humans," said lead scientist Prof Mark Davis.
"It could be food for thought to all the testosterone supplement takers out there."
The scientists, writing in the journal Proceedings of the National Academy of Sciences, said that the anti-inflammatory properties of testosterone might be linked to its role as a medication suppressant.
Davis speculated on the evolutionary reasons for this.
"Ask yourself which sex is more likely to clash violently with, and do grievous bodily harm to, others of their own sex," Davis added.
He said that male aggression was more likely to lead to physical injury, and testosterone may have had a role in supressing the immune system to prevent potentially fatal over-reactions to wounds.