By Matt McMillen
The list of reasons to quit smoking just got longer.
A new study published today on the website of the Archives of General Psychiatry has found that smoking appears to accelerate the pace of age-related cognitive decline in middle-aged men.
The mental function of the average 50-year-old male smoker can be expected to decline as quickly as that of a 60-year-old who has never smoked, the researchers estimate, even after factors such as educational level and overall health are taken into account.
"While we were aware that smoking is a risk factor for lung diseases, cancer, and cardiovascular disease, this study shows also its detrimental effect on cognitive aging," says lead author Severine Sabia, Ph.D., an epidemiologist at University College London, in the UK. "This detrimental effect is evident as soon as [age] 45."
And it's not just the pack-a-day crowd that needs to worry. So-called social smokers also put their brains at risk whenever they light up, the study suggests. "Intermittent smokers showed the same cognitive decline as persistent smokers, showing the importance of definitive smoking cessation," Sabia says.
Female smokers did not display similar declines, however -- an unexpected finding the researchers say may reflect gender differences in smoking and health patterns, rather than differences in how the brain responds to smoking.
"That is new and surprising," says Joseph Quinn, M.D., a neurologist at Oregon Health and Science University, in Portland, who was not involved in the new research. "While there are lots of possible explanations, all are speculative. But women are not off the hook."
Sabia and her colleagues analyzed data on 7,236 British civil servants who participated in a long-running health study known as Whitehall II. Over a 25-year period, the men and women periodically answered questions about their smoking habits: how old they were when they started to smoke; how much they smoked each day; and, if they'd quit, how long it had been since they kicked the habit.
Three times in 10 years, the same group also underwent a battery of tests designed to measure their short-term memory and their capacity to plan, organize, and pay attention (known as executive function). On average, the workers were 56 years old when they first took the brain tests.
Male smokers "showed a cognitive decline as fast as non-smokers 10 years older than them," Sabia says.
There was some good news. Former smokers who had been off cigarettes for at least ten years showed no increase in cognitive decline compared to men who had never smoked.
"Anyone who stops smoking reduces their risk," Quinn says.
One question the study can't answer is whether the cognitive decline the researchers measured can be linked to Alzheimer's disease and other forms of dementia, says David Teplow, Ph.D., interim director of the Mary S. Easton Center for Alzheimer's Research at UCLA, in Los Angeles.
"Are these people going to get diseases? That's what we want to know," Teplow says, adding that he hopes the researchers will continue to follow the study participants into old age, when a potential link between smoking and dementia would become apparent.
Previous research has identified smoking as a risk factor for dementia, but the extent of the association remains unclear, Sabia and her colleagues note.
In the meantime, the study's message for smokers is clear: Quit now.
"It is just that simple," Teplow says. "Live a healthy life, exercise, and eat a good diet. And a good diet means not inhaling cigarette smoke."