GENES rather than feeble will power may be letting down people who try and fail to give up smoking.
Scientists have identified genetic variants that increase a person's likelihood of becoming a lifelong heavy smoker. 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 to quit.
"Genetic risk accelerated the development of smoking behaviour," said study leader Dr Daniel Belsky, from Duke University in Durham, US.
"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 were reported in the scientific journal JAMA Psychiatry.