New York: Smoking cigarettes lowers intelligence, according to a study conducted by the Universityof Michigan.

Scientists studied 172 men – 66 of whom smoked – and gave them scores based on how quickly and accurately they responded to the tests. All smokers were allowed to smoke during the sessions, and it was found that in all the tests, smokers scored lower than non smokers.

The impact on memory, problemsolving and IQ was most pronounced among those who had smoked for years. Robert Zucker, a professor of Psychology at the University of Michigan, 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.’

The study adds to a growing body of evidence that smoking may affect mental ability. Last year, researchers found that it could increase the risk of dementia later in life.

Dr Jennifer Glass, of the University of Michigan’s Department of Psychiatry, called for more research to confirm the findings and to look at whether women smokers suffer similar memory problems.