X factor the key to longer life

SCIENTISTS may have figured out why women live longer than men – linking it to having two X chromosomes which defend against ageing, a new study says.

The extra X provides a sturdy cellular structure that protects against gene mutation and sickness, according to a report published in the journal Biology Letters.

For the study, scientists from the University of New South Wales gathered data on the sex chromosomes and lifespan of 229 species, including insects, fish and mammals.

They found that animals with two of the same sex chromosomes – such as birds with two “Z” chromosomes – live nearly 18 per cent longer.

Their research piggybacks on a pre-existing theory known as the “unguarded X hypothesis”, which notes that one X can serve as a buffer against disease. As the theory goes, only one X is activated in each of a woman’s cells, so a harmful mutation in one cell is less likely to affect all cells.

That makes mutation-related disorders “masked” more often in females, according to scientists. By contrast, guys are more likely to be exposed to the same types of mutations because their XY chromosomes only have a lone X.

But when the males of other species double up, they tend to live longer than females.

Overall, males live an average of 7 per cent longer than females in species where males have two of the same sex chromosomes, according to the study.

When the chromosome pattern is the other way around – as in the case of humans – women live an average of nearly 21 per cent longer than guys.