New evidence suggests that smoking isn't only bad for the body but can also take a toll on the mind.
A study published today in the Archives of General Psychiatry linked smoking to faster, more dramatic age-related mental decline in men.
Researchers from University College in London studied more than 5,000 men and 2,000 women from Britain's long-running Whitehall II study, which has surveyed the health of thousands of British civil service employees.
The researchers studied each participant's performance on tests of memory, verbal skills and reasoning over a period of 10 years, beginning when the participants were about 56 years old. They found that men who smoked showed a greater decline in these mental functions than those who had never smoked.
Smoking seemed to speed up the cognitive aging process, making men function mentally as if they were 10 years older, said Severine Sabia, the study's lead author.
"For example, a 50-year-old male smoker shows a similar cognitive decline as a 60-year-old male never-smoker," she said.
The brain changes weren't necessarily permanent. Men who stopped smoking more than 10 years before the tests performed as well as those who had never smoked. But men who kicked the smoking habit less than 10 years before the cognitive tests began didn't do much better than the men who'd kept smoking.
While smoking seemed to drain men's brains, the researchers didn't find a similar connection between smoking and declining mental function in women. Sabia said that could be because women in this age group smoked less than men do, or that there were simply fewer women in the study.
Researchers said there are several factors that could explain the connection between smoking and mental decline. One reason could lie in the way smoking affects the heart, lungs and blood vessels. Because smoking ups the risk of vascular disease, it could limit the body's ability to deliver the blood, oxygen and nutrients the brain needs to function at its best.
Dr. Charles DeCarli, director of the Alzheimer's Disease Center at the University of California at Davis, said differences in cardiovascular disease may also explain why the study found that men showed more cognitive decline linked to smoking than women did.
"Men have more heart disease and greater stroke risk than women do up until about age 70 or so. Part of that is related to lifestyle," DeCarli said. "Men of this age group often smoked more than women did."
Philip Harvey, a professor of psychiatry at the University of Miami School of Medicine, said the addictive nature of cigarettes may also take a toll on the brain, noting that molecules of nicotine in the brain latch onto the same brain receptors involved in attention, concentration and memory.
"That just may lead to a disregulation of those receptors, it may make them function less well," Harvey said. "But that could mean that rather than some kind of long-term damage, it's a reversible process that may involve resetting the receptors."
The study's authors said that smoking's long-term effects on mental function are probably underestimated, since smokers are more likely to die of other health problems before they have the chance to develop dementia.