CHICAGO (Reuters) - Middle-aged adults who smoke tended to perform poorly on tests of memory and reasoning compared to nonsmokers, adding to the list of reasons not to smoke, French researchers said on Monday.

Analyzing previously collected data on about 5,000 British civil servants, the researchers found those who smoked were more likely than people who never smoked to be in the lowest-performing of five groups in tests of memory, reasoning, vocabulary and verbal fluency.

Smoking was associated with mental decline in middle age, as it is with dementia and a host of physical ills later in life, they found.

"Smoking in middle age is associated with memory deficit and decline in reasoning abilities," concluded Severine Sabia and colleagues from the National Institute of Health and Medical Research in Villejuif, France.

Compared to smokers, people who said they had quit cigarettes were more likely to adopt healthier behaviors, such as drinking less alcohol, being more physically active, and eating more fruits and vegetables, Sabia reported in the journal Archives of Internal Medicine.

The participants were aged 35 to 55 at the beginning of the study, which followed some subjects up to 17 years.

The study also demonstrated how difficult it can be to conduct long-term research on smokers: more than twice as many smokers as non-smokers refused to take the memory test again or were not able to be re-tested, in some cases because they died in the interim.