Young smokers who have smoked more cigarettes have clear differences in their brains compared to lighter smokers, according to a new study.
"Earlier studies of older participants showed that the smokers had structural differences in various brain regions," said senior author Edythe D. London.
And in studies of adolescent animals, nicotine damaged and killed brain cells, added London, from the Semel Institute for Neuroscience and Human Behavior at UCLA and the David Geffen School of Medicine in Los Angeles.
"While the results do not prove causation, they suggest that there are effects of cigarette exposure on brain structure in young smokers, with a relatively short smoking history," London said.
She and her team at UCLA mapped the brains of 42 people ages 16 to 21 using magnetic resonance imaging (MRI) and asked them about their smoking history and cravings.
Eighteen of the participants were smokers. They had typically started smoking around age 15 and smoked six to seven cigarettes per day.
There were no clear differences in the brains of smokers versus non-smokers. However, among smokers, those who reported smoking more cigarettes tended to have a thinner insula, a region of the cerebral cortex involved in decision making, according to results published in the journal Neuropsychopharmacology. The effects seemed confined to the right insula.
Previous studies have suggested the insula plays a central role in tobacco dependence, with the highest density of nicotine receptors in the brain.
The researchers also found a thinner insula in the brains of people who had more cravings and felt more dependent on cigarettes. Their study was funded by Philip Morris USA, makers of Marlboro and Virginia Slims.
Young people ages 18 to 25 have the highest smoking rates in the U.S. at 30 percent, London said.
"Because the brain is still undergoing development, smoking during this critical period may produce neurobiological changes that promote tobacco dependence later in life," she said. Changing the structure of the insula may affect future smoking dependence and other substance abuse.
"It is possible that changes in the brain from prolonged exposure help maintain dependence," she said.
People who start smoking early in life seem to have more trouble quitting and have more serious health consequences than those who start later, London said.
But since the study only assessed smokers at one point in time, it doesn't prove that cigarettes changed their brains.
"It is possible that such changes pre-dated the smoking, i.e. they were not caused by smoking," Dr. Nasir H. Naqvi