Sabia and fellow NIHMR colleagues analyzed data from 10,308 civil servants located in London, England, with ages of 35 to 55 years at the beginning of the study.

Specifically, the researchers used the Whitehall II study, which was conducted between the years of 1985 and 1988. This portion of the study was considered phase 1.

In the Whitehall II study, the subjects were asked questions relating to their smoking habits. They were again asked the same questions between 1997 and 1999.

During this 1997-1999 time frame, 5,388 of the 10,308 subjects took five different performance tests involving memory, reasoning, vocabulary, and semantic and phonemic (verbal) fluency.

This was called phase 5 of the study.

The performance tests were given five years later to 4,659 of the 5,388 participants.

What were the results of the study? Please read on.

The French researchers found that subjects who smoked were more likely to have lower scores than people that had never smoked.