Smoking linked to higher dementia risk

Smokers have a higher risk of developing dementia, but giving up smoking can lower that risk, according to a new study in South Korea.

Long-term quitters and those who had never smoked had 14 per cent and 19 per cent lower risks for dementia, respectively, compared to smokers who kept up with the habit, the study authors reported in the Annals of Clinical and Translational Neurology.

"Smoking is well known for its thousands of negative health consequences, including cancers and cardiovascular diseases. However, its impact on our brain is relatively less emphasized," said lead study author Dr. Daein Choi of the Seoul National University College of Medicine. 

The article cites several case-control studies from the 1980s and 1990s that found smoking reduced the risk of Alzheimer's disease, but these studies were typically funded by tobacco companies. 

"There has been a misconception that the stimulant effect of nicotine might act as a protective factor for dementia," Choi told Reuters by email. 

Smoking and Alzheimer's risk

Choi and colleagues studied health claims from a national database in Korea, focusing on 46,000 men over age 60. Based on questionnaire responses, the researchers classified the men as continual smokers, short-term quitters of less than four years, long-term quitters of four years or more, and never smokers.

From the start of the study in 2002 until the end in 2013, 1,644 men were diagnosed with dementia.

Compared to continual smokers, long-term quitters and never smokers had a lower risk of dementia in general, and also a decreased risk of so-called vascular dementia, which is caused by poor blood flow to the brain. Never smokers also had a lower risk of Alzheimer's disease.

"The interesting point is that the increased risk of dementia related to smoking was reversible through smoking cessation," Choi said. "We would encourage smokers to quit to benefit from a reduced risk of dementia."

A limitation of the study is that it may not have been long enough to fully determine the effects of smoking cessation on
Alzheimer's disease, which starts slowly and worsens over time. Plus, smoking habits may have changed after the questionnaires were returned.

Quit to 'prevent or slow' dementia

Janine Cataldo of the University of San Francisco Center for Tobacco Control Research and Education, who wasn't involved in this study, told Reuters, "Smoking cessation could be a valuable and feasible intervention to prevent or slow the progression of dementia."

In a study published in 2010, Cataldo and colleagues reviewed previous research publications and found that smokers were almost two times more likely than non-smokers to develop Alzheimer's disease.

"The myth that smoking protects against Alzheimer's disease may discourage cessation attempts among older smokers and contribute to the reluctance of health care providers to treat tobacco dependence in older smokers," she said by 
email.

Additional studies should look at smoking cessation and dementia across different ethnicities, as well as with women,
Cataldo said.

"Given that smoking is a significant risk factor for cardiovascular disease and Alzheimer's disease, it makes sense that smoking cessation could become an integral part of the prevention and treatment of Alzheimer's disease," she said.