Adopting a smoking habit young may lead to a lifelong struggle with tobacco addiction, according to researchers at the University of Utah and their colleagues at the University of Wisconsin-Madison. The study adds to the argument for efforts to reduce the number of youths who begin smoking.

Investigators examined 2,827 long-term European American smokers, recruited in Utah and Wisconsin to the National Heart, Lung, and Blood Institute's Lung Health Study. They identified common genetic variations, called single nucleotide polymorphisms (SNPs), which impact nicotine receptors in the nervous system, significantly increasing the chance that the youths in the study will struggle with nicotine addiction throughout their lives.

"We know that people who begin smoking at a young age are more likely to face severe nicotine dependence later in life," explained Robert Weiss, PhD, professor of human genetics at the University of Utah and lead author of the study. "This finding suggests that genetic influences expressed during adolescence contribute to the risk of lifetime addiction severity produced from the early onset of tobacco use."

SNPs are changes in a single unit of DNA, which, linked and inherited together, are called a haplotype. One haplotype for the nicotine receptor put European American smokers at greater risk of heavy nicotine dependence as adults, but only if they began daily smoking before the age of 17, according to the study. A second haplotype reduced the risk of adult heavy nicotine dependence for people who began smoking in their youth.

The authors found that people who began smoking before the age of 17 and possessed two copies of the high-risk haplotype had a 1.6-fold to almost 5-fold increase in risk of heavy smoking as an adult. For people who began smoking at age 17 or older, presence of the high-risk haplotype did not significantly influence their risk of later addiction.

"In recent years we've seen an explosion in the understanding of how small genetic variations can impact all aspects of health, including addiction. As we learn more about how both genes and environment play a role in smoking, we will be able to better tailor both prevention and cessation programs to individuals," said Nora D. Volkow, MD, director of the National Institute on Drug Abuse (NIDA),

The research was published in the July 11 issue of PLoS Genetics. The study was funded in part by NIDA and the National Heart, Lung, and Blood Institute, both part of the National Institutes of Health.