In a typical smoker of 18 to 21, the average IQ was 94, while abstainers 101. For more smokers pack a day, it did not exceed 90 although other indicators for all participants in the study were the same.
For now, scientists are unable to explain the exact mechanism by which smoking lowers intelligence, but are willing to accept that in some cases this is already a known fact - people with lower IQ more often heavy smokers.
Let us remind that low IQ is one of the truest signs of a tendency to heart disease. More precisely, it is second only to smoking, and only afterwards, blood pressure, and sedentary lifestyle.