OVERWEIGHT people can add about a year to their life for every stone they shed, according to Scottish research.

Scientists say that every extra kilogram (2.2lb) they carry cuts life expectancy by two months and means that if an obese person was to lose five stone, they could live about five years longer.

Obesity levels today are more than three times what they were in 1980, when only six per cent of men and eight per cent of women were obese.

The major genetic analysis also found education leads to a longer life, with almost a year added for every 12 months spent studying beyond school.

Other key findings included giving up smoking, which can lead to seven years’ extra life or more.

Being open to new experiences might also help people live longer, said the University of Edinburgh team, whose findings are published in Nature Communications.

They said learning and staying in shape are the keys to a long and healthy life.

Dr Peter Joshi, a Chancellor’s Fellow specialising in the genomic basis of lifespan in humans, said: “Our study has estimated the causal effect of lifestyle choices.

“We found that, on average, smoking a pack a day reduces lifespan by seven years, whilst losing one kilogram of weight will increase your lifespan by two months.”

Dr Joshi and colleagues analysed genetic information from more than 600,000 people alongside records of their parents’ lifespan.

As people share half of their genetic information with each of their parents, the team were able to calculate the impact of various genes on life expectancy.

Lifestyle choices are influenced to a certain extent by our DNA. Genes, for example, have been linked to increased alcohol consumption and addiction.

This allowed the researchers to work out which have the greatest influence on lifespan. Their method was designed to rule out the chances any observed associations could be caused by a separate, linked factor.

This enabled them to pinpoint exactly which lifestyle factors cause people to live longer, or shorter, lives.

They found that cigarette smoking and traits associated with lung cancer had the greatest impact on shortening lifespan.

For example, smoking a packet of cigarettes per day over a lifetime takes an average of seven years off life expectancy, they calculated. But smokers who give up can eventually expect to live as long as somebody who has never smoked.

Body fat and other factors linked to diabetes also reduce life expectancy.

The study also identified two new DNA differences that are vital. The first, in a gene that affects blood cholesterol level, reduces lifespan by about eight months.

The second, in a gene linked to the immune system, adds around half a year to life expectancy.