Drinking higher quantities of alcohol and smoking cigarettes are both linked to a lower IQ, research finds.
People who smoke and drink have a worse memory and poorer problem-solving skills.
Similarly, higher rates of binge drinking are also linked to a lower IQ, a previous study found.
Smoking may be even more damaging to thinking skills than drinking.
High levels of smoking and drinking both lead to a slower brain and making more mistakes.
The reason may be that smoking and drinking damage the blood vessels supplying the brain.
The conclusions come from a study of 172 men, some of whom were alcoholics.
All completed tests of IQ, memory and thinking skills and were followed up over nine years.
The results showed that the more they drank and smoked, the lower their IQ.
Drinkers and smokers also had worse memories and poorer thinking skills.
Dr Jennifer Glass, the study’s first author, said:
“We can’t say that we’ve found a cause-and-effect relationship between smoking and decreased thinking ability, or neurocognitive proficiency.
But we hope our findings of an association will lead to further examination of this important issue.
Perhaps it will help give smokers one more reason to quit, and encourage quitting smoking among those who are also trying to control their drinking.”
Professor Robert Zucker, study co-author, said:
“The exact mechanism for smoking’s impact on the brain’s higher functions is still unclear, but may involve both neurochemical effects and damage to the blood vessels that supply the brain.
This is consistent with other findings that people with cardiovascular disease and lung disease tend to have reduced neurocognitive function.”
The study was published in the journal Drug and Alcohol Dependence (Glass et al., 2006).