Mitochondrial DNA may hold answer to why women live longer than men

Scientists working on fruit flies say their work provides an answer to the question of why women tend to live longer than men. The research points to mitochondria, the 'batteries' within cells that generate energy, as hotspots for mutations that negatively affect male health.

Researchers from Lancaster University in the UK and Monash University in Australia studied the ageing of 13 different strains of fruit fly. They found that mutations in the mitochondrial DNA affected the how long male flies lived, and how fast they aged.

'Intriguingly, these same mutations have no effects on patterns of ageing in females', Dr Damian Dowling, of Monash University said. 'Our results therefore suggest that the mitochondrial mutations we have uncovered will generally cause faster male ageing across the animal kingdom'.

Mitochondria were already thought to play a role in ageing: in producing energy from oxygen, they also produce free radicals, which can harm the cell. Dr Dowling and colleagues have now found indications that this might be particularly true for males.

'All animals possess mitochondria, and the tendency for females to outlive males is common to many different species', Dr Dowling explained. 'While children receive copies of most of their genes from both their mothers and fathers, they only receive mitochondrial genes from their mothers. This means that evolution's quality control process, known as natural selection, only screens the quality of mitochondrial genes in mothers'.

The idea of mitochondrial DNA in males not being subject to natural selection and therefore leading to male-only harmful mutations, is known among geneticists as the 'mother's curse'.

Dr Dowling added: 'If a mitochondrial mutation occurs that harms fathers, but has no effect on mothers, this mutation will slip through the gaze of natural selection unnoticed. Over thousands of generations, many such mutations have accumulated that harm only males, while leaving females unscathed'.

But the results should be interpreted with caution. So far, the sex-specific ageing effects of mutations in mitochondrial DNA have only been found in fruit flies and have to be confirmed in other species.

Professor Tim Kirkwood of Newcastle University, who was not involved in the study, told BBC News: 'There are other things we know also count - lifestyle, social and behavioural factors. But the biggest difference in biology is that we have different hormones. I certainly don't think this is a discovery that explains why women live five-to-six years longer than men'.