Does Smoking Cause Dementia? Study Finds Higher Risk Link

From heart disease to cancer, smoking comes with a range of health risks. Researchers have warned that dementia shouldn't be left off that list.

Scientists based in South Korea found a connection between smoking and dementia by studying 46,140 men at least 60 years old who were registered to a population-based screening program from 2002 to 2013. Participants detailed their smoking habits on a questionnaire completed between 2002 and 2003, and again in 2004 and 2005.

Starting in 2006, researchers assessed the men for eight years to see if they developed dementia as well as Alzheimer's disease or vascular dementia (two of the most common forms of dementia). Women were not included in the study due to extremely low rates of smoking among that demographic in South Korea, the authors said.

The men were categorized as continual smokers; short-term quitters who had kicked the habit in the previous four years or less; long-term quitters at four years or more; or men who had never smoked.

The findings, published in Annals of Clinical and Translational Neurology, showed that former smokers who had quit long-term, and those who had never smoked, had a 14 percent and a 19 percent lower risk, respectively, of developing dementia from the baseline, compared with those who lit up regularly.

When Alzheimer's was considered, nonsmokers had an 18 percent lower risk than those who smoked cigarettes. Meanwhile, the vascular dementia risk for long-term quitters and those who had never smoked was 32 percent and 29 percent lower, respectively.

Read more: Skinny fat body time linked to dementia in study

The authors concluded that smoking was associated with an increased risk of dementia. But ex-smokers who'd kicked the habit for a long period could reverse the risk to some extent.

Co-author Dr. Daein Choi of the Department of Biomedical Sciences, Seoul National University College of Medicine, told Newsweek: "The interesting part of our result was that smoking quitters had decreased risk of developing dementia compared to those who smoked continuously. We were quite surprised because the effect of smoking on our nervous systems might have been irreversible since the neurons of our nervous system have a very little regenerative capacity."

Choi continued: "We would like to highlight smoking as a risk factor for dementia. Our findings would also encourage smokers to quit in order to benefit from reduced risk of dementia."

Around one-third of the world's population age 15 or over smokes, according to the World Health Organization. In the U.S., more than 16 million Americans are living with a disease likely caused by smoking, and the behavior causes more than 480,000 deaths per year.

Rates of smoking are dropping, but health officials are still tackling dementia. Rates of dementia (a syndrome characterized by factors such as memory loss) are expected to triple by 2050, according to the World Health Organization. But there is no cure for the condition, nor is there a definitive cause of it. Scientists are therefore dedicated to exploring every possible contributing factor to its development, from genetics to lifestyle factors such as smoking.

"The toxic chemicals in cigarettes can increase oxidative stress and inflammation, which have both been linked to the development of Alzheimer's disease. Smoking also increases the chance of developing other health conditions like type 2 diabetes, which in turn elevate the likelihood of dementia," commented Dr. Sara Imarisio, head of the charity research at Alzheimer's Research U.K., who was not involved in the study.

Imarisio advised those concerned about developing dementia to "drink within the recommended guidelines, stay physically fit, eat a balanced diet and keep your blood pressure and cholesterol levels in check."

Researchers from Seoul National University College of Medicine and Seoul National University Hospital collaborated on the study.

This article has been updated with comment from Dr. Daein Choi​.