Smokers may in future be able to blame their genes for their addiction. Researchers have identified three genetic mutations that increase the number of cigarettes people smoke a day. Several also appear to be associated with taking up smoking, and one affects how difficult individuals find it to stop.
The findings, based on data from more than 140,000 individuals and published in Nature Genetics, will be incorporated into DNA tests developed by the Icelandic company deCODE, to tell people what risk they run of becoming smokers.
A statement from deCODE, which took part in the research, said that, taken together, the variants identified a "sizeable proportion" of smokers whose health was at greater risk than average because of their habit.
Dr Kari Stefansson, the chairman of deCODE and one of the researchers from 23 institutions in a dozen countries, said: "Smoking is bad for anyone's health. It is even worse for some, and today's discoveries continue to strengthen our ability to identify who those people are and give them a compelling additional reason to quit."