The study, carried out by researchers at Karolinska Institutet and Karolinska University Hospital, is based on the military enlistment exams of 49,000 men born between 1949 and 1951. The men took IQ tests and also answered questions about their smoking and alcohol habits.
The results of the study, which were published in the latest issue of the Journal of Epidemiology, indicated a 15 percent increase in the risk of dying at age 53 for every step down on a nine-level intelligence scale.
But when researchers excluded other known risk factors, such as smoking and alcohol consumption, the relationship entirely disappeared. Instead, it indicated that the root of the problem was that men with lower intelligence often had more unhealthy lifestyles.