Smoking accelerates up mental decline in men, making their cognitive deterioration equivalent to non-smokers who are 10 years older, psychiatrist found in a study released on Monday.

While British researchers found in a large, long-term study that smoking appeared to be associated with rapid declines in memory, thinking, learning and processing information in men, smoking did not appear to be associated with these mental declines in women.

Researchers said that the habit is linked with early dementia-like cognitive difficulties that can show up as early as the age of 45 in men, and that a 50 year old male smoker would show a similar cognitive decline exhibited in a 60 year old male never smoker.

Dr. Séverine Sabia, of University College London and his team based their research on data from the Whitehall II cohort study that consisted of 5,099 men and 2,137 women who were British Civil Service employees with an average age of 56 years at the first mental assessment. 

The assessment included five tests that measured participants’ memory, vocabulary, verbal and math skills.  Participants were tested three times, with the initial evaluation at midlife, then once every five years over a decade.

Researchers analyzed data using six assessment of smoking status over a span of 25 years and three cognitive assessments over a decade and found that not only is smoking associated with a more rapid cognitive decline in male smokers, but men who continued to smoke over the follow-up period of the study had displayed greater decline in cognitive ability.

Researchers noted that men who quit smoking in the 10 years before their first cognitive tests were still at risk of greater mental deterioration, particularly in higher level cognitive processes in planning.  However “long-term ex-smokers” did not show faster cognitive decline.

"Finally, our results show that the association between smoking and cognition, particularly at older ages, is likely to be underestimated owing to higher risk of death and dropout among smokers," the authors concluded.

Study authors said that they are still unsure to why their results demonstrated a link between smoking and mental declines in men but not in women, but they suggested that the sex difference could be due to the fact that men smoke more tobacco compared to women. 

Study authors said that smoking is increasingly recognized as a risk factor for dementia in the elderly and as a contributor in the number of dementia cases worldwide.  They estimated that there were 36 million cases of dementia in 2010, and the number of these cases is projected to double every 20 years, according to previous research.

Cognitive decline can now be added to the long list of tobacco health hazards, like the increased risk for lung cancer, other chronic respiratory diseases and cardiovascular diseases. 

"While we were aware that smoking is a risk factor for respiratory disease, cancer, and cardiovascular disease, this study shows it also has a detrimental effect on cognitive ageing and this is evident as early as 45 years," said Sabia told Fox News.

The study is published in the Archives of General Psychiatry.