Smoking is directly related to lower IQ, according to a study by researchers at Tel Aviv University in Israel and published in the journal Addiction.

The researchers tested the IQ of more than 20,000 healthy men aged 18 to 21 who were serving in the Israeli army or who have recently completed their service. Twenty-eight percent of men in the sample smoked, while 3 percent were former smokers and 68 percent had never smoked.