The tendency for smart people to live longer is down to their genes, scientists have revealed for the first time.

Researchers analysing data from twins found that 95 per cent of the link between intelligence and life expectancy is genetic.

They found that, the brighter twin tends to live longer and noted the pattern was much more pronounced in fraternal - non identical - twins, than identical pairs.

By looking at both fraternal twins - who only share half their twin's DNA - with identical twins, helps researchers distinguish between genetic effects and environmental factors, including housing, schooling and childhood nutrition.

A study has found 95 per cent of the link between intelligence and life expectancy is genetic, for the first time

Rosalind Arden, a research associate at the London School of Economics, said: 'We know that children who score higher in IQ-type tests are prone to living longer.

'Also, people at the top of an employment hierarchy, such as senior civil servants, tend to be long-lived.

'But, in both cases, we have not understood why.'

'Our research shows that the link between intelligence and longer life is mostly genetic.

'So, to the extent that being smarter plays a role in doing a top job, the association between top jobs and longer lifespans is more a result of genes than having a big desk.'

However, Dr Arden said it is important to note that the association between IQ and lifespan is small.

'You can't, for example, deduce your child's likely lifespan from how he or she does in their exams this summer,' she said.

To arrive at their conclusions, Dr Arden and her team looked at three different twin studies from Sweden, the US and Denmark.

Both intelligence and the age of death was recorded in each study, and in each, at least one twin in each pair had died.

Researchers found that, the brighter twin tends to live longer and noted the pattern was much more pronounced in fraternal - non identical - twins, than identical pairs

Only twins of the same sex were included in the study.

Exploring the reasons for their findings, Dr Arden said it is possible that people whose genes make them intelligent, may also benefit from good DNA that improves health.

'It could be that people whose genes make them brighter also have genes for a healthy body,' she said.

'Or intelligence and lifespan may both be sensitive to overall mutations, with people with fewer genetic mutations being more intelligent and living longer.

'We need to continue to test these ideas to understand what processes are in play.'