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Smoking and Dementia: What You Need to Know

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Doctors have long known that smoking cigarettes and other tobacco products increases the risk for a host of illnesses, including heart disease, stroke and lung cancer. While the relationship between smoking and dementia has been less clear, a growing body of scientific research conducted over the last decade suggests a strong connection.

Although the results from these observational studies can’t establish a direct causal relationship (in other words, they don’t prove that smoking causes dementia), they do provide powerful evidence that inhaling tobacco smoke exposes the brain to toxic conditions that may cloud cognition. In fact, the World Health Organization now estimates that smoking may be responsible for up to 14 percent of all cases of Alzheimer’s disease (AD), the most common form of dementia. Fortunately, there’s also evidence to suggest that kicking the habit can minimize that risk.

Multiple mechanisms

A 2015 analysis published in the online scientific journal PLOS ONE evaluated the results of 37 studies that compared current smokers with people who never smoked or who quit. The authors found that current smokers were 30 percent more likely to develop some form of dementia than people who never smoked. When researchers looked more closely, they found a 40 percent increased risk for AD among smokers and a similar risk for vascular dementia. Some earlier studies suggest that the increased risk for dementia among smokers may be even greater.

Smoking appears to lead to cognitive decline in a number of ways. For example, inhaling tobacco smoke triggers a phenomenon known as oxidative stress, which harms the DNA in cells throughout the body, including the brain. Oxidative stress appears to promote the formation of amyloid plaques and neurofibrillary tangles in the brain; both are closely associated with AD.

Also, tobacco smoke damages arteries, which interferes with the free flow of blood to the brain. Depriving neurons, or brain cells, of the oxygen and nutrients in blood can cause them to die and lead to vascular dementia, the second most common form of age-related cognitive decline after AD. Smoking also boosts levels of the amino acid homocysteine and inflammation, both of which have been linked to dementia.

Studies indicate that smoking’s impact on dementia risk is dose-dependent—that is, the more you smoke, the greater your risk. Other research suggests that nonsmokers who are exposed to tobacco smoke face an increased risk for severe dementia. In one study, published in 2013 in Occupational and Environmental Medi- cine, researchers tested the cognitive skills of nearly six thousand men and women aged 60 and older who lived in China. They also asked the study participants (or their caregivers) about their exposure to environmental, or “secondhand,” tobacco smoke.

The researchers found that people who had been exposed to secondhand smoke were 29 percent more likely, on average, to have dementia than those who had not been exposed. An analysis of data from a subgroup of participants followed for several years revealed that individuals exposed to secondhand smoke for five to nine years were 66 times more likely than those with no exposure to have developed severe dementia.

Scientists know less about the effects of smokeless tobacco (such as chewing tobacco and snuff) on dementia risk because of limited research in this area. One 2011 study in the International Journal of Geriatric Psychiatry failed to find a significant association. Still, smokeless tobacco has been shown to increase the risk for a number of serious conditions, including heart disease and oral cancer.

Research suggests that if you smoke, quitting is one of the single best steps you can take. The PLOS ONE analysis found that over time, people who quit smoking lowered their risk of developing dementia to the level of never smokers. However, an earlier review published in the American Journal of Epidemiology found that people who quit smoking were, nonetheless, more likely than others who never smoked to experience some loss of cognitive skills as they aged; but the authors also found that people who gave up tobacco eventually had the same risk for dementia as never smokers.

 

Posted in Memory on May 3, 2016


Medical Disclaimer: This information is not intended to substitute for the advice of a physician. Click here for additional information: Health After 50 Disclaimer


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