Alcoholics who smoke have more problems with memory, problem solving and quick thinking than those who are nonsmokers, researchers have found.
This "early aging" of the brain gets worse over time, according to the study published online May 17 and in the October print issue of Alcoholism: Clinical & Experimental Research.
The study measured mental or "cognitive" functioning.
"The independent and interactive effects of smoking and other drug use on cognitive functioning among individuals with [alcohol dependence] are largely unknown," Alecia Dager, an associate research scientist in the department of psychiatry at Yale University, said in a journal news release. "This is problematic because many heavy drinkers also smoke. Furthermore, in treatment programs for alcoholism, the issue of smoking may be largely ignored," she noted.
For the study, adult participants were divided into four groups. The first included 39 healthy people who never smoked. The other groups included people seeking treatment for alcoholism after not drinking for one month. Of these, 30 people had never smoked, 21 were former smokers and 68 were current smokers.
According to study corresponding author Timothy Durazzo, the investigators "focused on the effects of chronic cigarette smoking and increasing age on cognition because previous research suggested that each has independent, adverse effects on multiple aspects of cognition and brain biology in people with and without alcohol use disorders."
The researchers analyzed participants' mental ability in a number of areas.
Durazzo, who is an assistant professor in the department of radiology and biomedical imaging at the University of California, San Francisco, said in the news release that "at one month of abstinence, actively smoking [alcohol-dependent participants] had greater-than-normal age effects on measures of learning, memory, processing speed, reasoning and problem-solving, and fine motor skills."
In contrast, among participants with alcohol problems, "never-smokers and former-smokers showed equivalent changes on all measures with increasing age as the never-smoking controls," he explained.
"These results indicate the combination of alcohol dependence and active chronic smoking was related to an abnormal decline in multiple cognitive functions with increasing age," Durazzo said, and that "the combined effects of these drugs are especially harmful and become even more apparent in older age."
He pointed out that other factors, including nutrition and exercise, may also influence brain function during early abstinence. He added that underlying medical issues including high blood pressure and diabetes as well as psychiatric conditions such as depression and post-traumatic stress disorder could also play a role.
Based on their findings, the authors suggested that as people get older, chronic smoking and heavy drinking are associated with increased oxidative damage to the brain.
"Oxidative damage results from increased levels of free radicals and other compounds that directly injure neurons and other cells that make up the brain. Cigarette smoking and excessive alcohol consumption expose the brain to a tremendous amount of free radicals," Durazzo explained.
While the study tied alcohol dependence combined with smoking to early brain aging, it didn't establish a cause-and-effect relationship.
The researchers advised that people seeking treatment for alcohol abuse should also be routinely offered help to quit smoking.