Cigarette smokers have lower IQs than non-smokers, and the more a person smokes, the lower their IQ

From Reuters:

Young men who smoked a pack of cigarettes a day or more had IQ scores 7.5 points lower than non-smokers in a study of over 20,000 Israeli military recruits.

"Adolescents with poorer IQ scores might be targeted for programs designed to prevent smoking," concluded the researchers in the journal Addiction.

The average IQ for non-smokers was 101, while it was 94 for men who had started smoking before entering the military. IQ steadily dropped as the number of cigarettes smoked increased, from 98 for people who smoked one to five cigarettes daily to 90 for those who smoked more than a pack a day. IQ scores from 84 to 116 are considered to indicate average intelligence.

The study may suggest that lower IQ individuals are more likely to choose to smoke, rather than that smoking makes people less intelligent.

References:

http://www.reuters.com/article/idUSTRE61M3UQ20100223
The Physician in US Cigarette Advertisements, 1930–1953 (illustrated review) http://1.usa.gov/VcuA7W via @Skepticscalpel

Comments from Google Buzz:

Dr Mike Cadogan - By definition non-smokers smarter than smokers...

Ben Ferguson - That's a weird conclusion to come to, in my opinion. They associated essentially pack-years with intelligence, which would seem to indicate a dosage effect, but then the suggestions were that they had lower IQs to begin with? It's a bit of a non sequitur. That there's a dosage effect would suggest that most of them had equal IQs before starting smoking; to conclude that they started smoking as a result of having lower intelligence to begin with has nothing to do with their aims and even undermines their findings.

Lakshman Swamy - Smoking is an addiction, and the smoking population is marginalized as it is. Obviously smoking is terrible for you... but let us not forget that smokers need healthcare and health advice more than most. I worry that this will further a "judging" attitude on the part of physicians.

Arin Basu - There is a problem in reducing entities like intelligence to single numbers like IQ scores (this is an offhand comment, I have not read /this/ particular article), but talking of programme targetting on the basis of studies that go to suggest "if you have low IQ then you smoke", in other words, implicitly accepting low IQ as /cause/ of smoking is dangerous. Well spotted though.

Image source: Wikipedia, Tomasz Sienicki, Creative Commons Attribution ShareAlike 2.0 License.