Women have twice as many X-chromosomes as men, which gives them a much stronger immune system and means they also live longer

For women pouring scorn on their male counterparts' susceptibility to "man 'flu", be kind on them – it may simply be due to genetic inferiority.

Women have a built-in advantage to their immune system because they have two X-chromosomes rather than one, research suggests, providing possible evidence for why they live longer and are more likely to recover from cancer than men.

The findings have resulted from a study of RNA, one of the three macromolecules along with DNA and proteins that are essential to all forms of life, and the tiny strains of this chemical known as microRNA that are encoded in the X-chromosome.

Dr Claude Libert, of Ghent University in Belgium, explained that some MicroRNAs can weaken the ability to resist illness and disease by "silencing" immunity genes. However, because women have two X-chromosomes, their bodies are more likely to be able to compensate than men's.

"Statistics show that in humans, as with other mammals, females live longer than males and are more able to fight off shock episodes from sepsis, infection or trauma," he said.

"We believe this is due to the X-chromosome which in humans contains 10 per cent of all MicroRNAs detected so far in the genome. The roles of many remain unknown, but several X-chromosome-located strands of MicroRNA have important functions in immunity and cancer."

Dr Libert, who co-authored the research, said the results could have important implications in the search for more effective drugs or better treatments for cancer. "How this unique form of genetic inheritance influences X-chromosome linked microRNAs will be a challenge for researchers for years to come," he said, "not only from an evolutionary point of view, but also for scientists investigating the causes and cures of disease."

Women should perhaps not be celebrating too much at the news, however. The paper, published today in the journal BioEssays, also noted that "the same mechanisms that endow females with a survival advantage also increase their susceptibility to autoimmune disorders later in life."