Every smoker is aware their habit puts them at risk of disease and early death – yet many still live to a ripe old age.
Now, scientists have discovered it may be down to their genes.
Smokers who live for a long time may have specific genes promoting a lengthy lifespan, a US study has found.
And these “longevity” genes were also linked with an 11 per cent lower incidence of cancer.
Scientists say the genes help the body’s cells maintain and repair themselves, protecting the person from ageing, and environmental damage like smoking.
Tobacco kills up to half of its users, figures from the World Health Organisation show.
It says the tobacco epidemic is “one of the biggest public health threats the world has ever faced”, killing around 6 million people a year.
According to the American Cancer Society, tobacco use accounts for at least 30 per cent of all cancer deaths, causing 87 per cent of lung cancer deaths in men, and 70 per cent of lung cancer deaths in women.
And a body of previous research has suggested that smoking accelerates the ageing process and cause disease and an early death.
But not all smokers die early, and a small proportion survive to an old age, researchers noted.
To investigate why, they studied smokers who lived for a long time.
They identified these people had a variant of a gene that allowed them to better withstand environmental damage, like the chemicals from cigarettes.
This gene was strongly linked with a high survival rate.
The study’s author, Morgan Levine, of UCLA, said: “We identified a set of genetic markers that together seem to promote longevity.
“What’s more, many of these markers are in pathways that were discovered to be important for ageing and lifespan.”
They may extend a person’s lifespan by helping their cells repair themselves, she added.
Ms Levine continued: “Therefore, even though some individuals are exposed to high levels of biological stressors, like those found in cigarette smoke, their bodies may be better set up to cope with and repair the damage.”
And the same genes might also be important to prevent cancer, the researchers said.
The study found they were associated with a nearly 11 per cent lower incidence of the disease.
The research was published in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences.
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