Tracking 18- to 21-year-old men enlisted in the Israeli army, researchers from Tel Aviv University say they have demonstrated an important connection between the number of cigarettes young males smoke and their IQ--young men who smoke are likely dumber than their non-smoking peers.

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.

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% said they never smoked.

The study illuminates a general trend in epidemiological studies, the authors say. "People on the lower end of the average IQ tend to display poorer overall decision-making skills when it comes to their health," says Mark Weiser of Tel Aviv University's Department of Psychiatry.

The  finding can help address a serious concern among health counselors at grade and high schools. Schoolchildren who have been found to have a lower IQ can be considered at risk to begin the habit, and can be targeted with special education and therapy to prevent them from starting or to break the habit after it sets in.

"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."

Making the results more significant, 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.