Smoking makes a person dumb

Young men who smoke are likely to have lower IQs than their non-smoking peers, a new study has determined.

The study led by Prof Mark Weiser of Tel Aviv University's Department of Psychiatry and the Sheba Medical Center at Tel Hashomer Hospital tracked 18- to 21-year-old men enlisted in the Israeli army.

The average IQ for a non-smoker was about 101, while the smokers' average was more than seven IQ points lower at about 94, the study determined.

The IQs of young men who smoked more than a pack a day were lower still, at about 90. An IQ score in a healthy population of such young men, with no mental disorders, falls within the range of 84 to 116.

"In the health profession, we've generally thought that smokers are most likely the kind of people to have grown up in difficult neighborhoods, or who've been given less education at good schools," says Prof Weiser, whose study was reported in a recent version of the journal Addiction. "But because our study included subjects with diverse socio-economic backgrounds, we''ve been able to rule out socio-economics as a major factor."

The study also measured effects in twin brothers. In the case where one twin smoked, the non-smoking twin registered a higher IQ on average.

Although a lower IQ may suggest a greater risk for smoking addiction, the cross-sectional data on IQ and smoking found that most of the smokers investigated in the study had IQs within the average range nevertheless.

In the study, the researchers took data from more than 20,000 men before, during and after their time in the military. All men in the study were considered in good health, since pre-screening measures for suitability in the army had already been taken. The researchers found that around 28 percent of their sample smoked one or more cigarettes a day, 3 percent considered themselves ex-smokers, and 68 percent said they never smoked.

"People on the lower end of the average IQ tend to display poorer overall decision-making skills when it comes to their health," says Prof Weiser.

"People with lower IQs are not only prone to addictions such as smoking," Prof Weiser adds. "These same people are more likely to have obesity, nutrition and narcotics issues. Our study adds to the evidence of this growing body of research, and it may help parents and health professionals help at-risk young people make better choices."

Photograph: Stringer India / Reuters