Willpower not enough to quit

Scientists from Duke University in Durham, the US, have identified genetic variants that increase a person’s likelihood of becoming a lifelong heavy smoker.

Participants with a high-risk genetic profile were more likely to smoke every day as teenagers

Those affected are more easily hooked as teenagers and quickly progress to smoking 20 or more cigarettes a day.

As adults, they find it harder to quit the habit than individuals with a different genetic make-up.

Researchers studied almost 1,000 New Zealanders from birth to the age of 38 to identify those at a greater genetic risk of smoking.

Participants with a high-risk genetic profile were more likely to smoke every day as teenagers. At 38, they had smoked heavily for more years, were more susceptible to nicotine addition, and were more likely to have failed in attempts to quit.

“Genetic risk accelerated the development of smoking behaviour,” said study leader Daniel Belsky. “Teens at a high genetic risk transitioned quickly from trying cigarettes to becoming regular, heavy smokers.”

Genetic make-up did not affect whether or not a person would try smoking for the first time.

But for individuals who did try cigarettes, having high-risk variants increased the chances of heavy smoking and tobacco dependence.

The results, reported in the journal Jama Psychiatry, are based on genetic risk scores derived from previous studies that scoured the whole genetic code for associations with smoking.

Alterations in the DNA in and around genes that affect the brain and body’s responses to nicotine were more common in the heaviest smokers.

How the specific variants affect gene function is not yet known.

DNA samples from the New Zealand group of 880 men and women of European descent were checked to see if they matched the smoking risk profile.

In total, 70 per cent of the participants had tried smoking, but this was not related to genetic risk. Those who smoked just one or two cigarettes a day, or only lit up at weekends, had an even lower genetic risk than non-smokers. But a strong association was seen between having a high-risk genetic profile and problem smoking.

Among teens who had tried cigarettes, those with the genetic variants were 24 per cent more likely to become daily smokers by the age of 15, and 43 per cent more likely to be smoking a 20-pack a day by 18.

As adults, people with high-risk genetic profiles were 27 per cent more likely to become nicotine dependent and 22 per cent more likely to fail at quitting. By the age of 38, a heavy smoking study participant with a high-risk genetic make-up had smoked about 7,300 more cigarettes than the average smoker.

Those who did not become regular heavy smokers in their teens appeared to be protected against the perils of tobacco as adults.