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Smoking and Dementia: What to Know

Doctors have long known that smoking cigarettes and other tobacco products increases the risk of 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, the most common form of dementia. Fortunately, there’s also evidence to suggest that kicking the habit can minimize that risk.

What's the connection?

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 Alzheimer’s disease 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 Alzheimer’s disease.

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 Alzheimer’s disease. 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 Medicine, researchers tested the cognitive skills of nearly 6,000 men and women age 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.

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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.

Quitting: It’s tough but worth it

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.

On the downside, quitting smoking can be a challenge. Many people end up requiring several attempts before they are finally able to kick the tobacco habit. Yet it’s worth remembering that nicotine is addictive, which helps explain why relapses are so common.

Kicking the habit

According to the Centers for Disease Control and Prevention, a majority of quitters “go it alone,” and don’t seek out treatments or assistance. But there are a number of smoking-cessation aids available that can improve your odds for success.

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A good place to start is by talking to your doctor. Research shows that people who ask their physicians for help are more likely to quit for good. A bit of advice from your doctor may be all you need, but he or she can also prescribe medications proven to aid smoking cessation. The three most widely used are nicotine replacement therapy, varenicline (Chantix), and bupropion (Zyban).

• Nicotine replacement therapy. These products provide a controlled amount of nicotine without exposing you to tobacco smoke and are designed to wean you off of cigarettes. Nonprescription nicotine replacement therapy products are available as transdermal patches, chewing gum, and lozenges. Prescription-only products are available in oral and nasal spray formulations.

• Varenicline. This prescription medication, available in the United States since 2006, blocks the pleasurable effects of nicotine in the brain and reduces craving and withdrawal symptoms.

• Bupropion. Originally developed as an antidepressant, bupropion can also help ease craving and withdrawal symptoms in people who quit smoking.

A 2013 review of pharmacological interventions for smoking cessation found that all three medications help boost the odds, at least somewhat, of remaining smoke-free.

The review, which was published by a nonprofit independent scientific organization called the Cochrane Collaboration, found that varenicline appears to work best, while bupropion and nicotine replacement therapy are about equally effective.

Findings from the review also showed that combining two forms of nicotine replacement therapy (such as a patch and gum) works as well as varenicline. (Both varenicline and bupropion carry warnings that they may cause psychological problems such as suicidal thoughts, though the evidence supporting that claim has been questioned.)

Studies suggest that people who seek counseling have higher success rates than those who quit on their own, so you may want to consider seeing a healthcare provider with experience in smoking cessation. However, it’s unclear whether one-on-one sessions are superior to group therapy.

Some therapists offer smokers alternative treatments, although most haven’t been well studied. One 2014 study conducted at several Massachusetts hospitals found that 44 percent of smokers who participated in hypnotherapy sessions were still abstaining from tobacco after three months, compared with 28 percent using nicotine replacement therapy.

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Finally, some smokers report being able to quit or cut back on tobacco by switching to electronic cigarettes. These devices heat liquids and certain chemicals, which may or may not include nicotine, to produce a vapor that’s inhaled. A [2014 Cochrane review](http://circ.ahajournals.org/content/129/19/1945 short) identified several studies examining whether “e-cigarettes” help smokers quit. Unfortunately, the Cochrane group found that the quality of these studies was generally poor. Overall, there’s too little known about e-cigarettes to say whether they’re safe, much less an effective intervention for quitting tobacco.

If you’re ready to kick the habit, you may be able to look to your insurer for financial assistance. Under the Patient Protection and Affordable Care Act, private health insurance providers must cover at least two stop-smoking attempts annually, with no copayment and without the need for prior authorization.

An attempt includes four tobacco-cessation counseling sessions (telephone, group, or individual) and use of any Food and Drug Administration-approved prescription or nonprescription smoking cessation medication for 90 days when prescribed by a healthcare provider. Medicaid smoking cessation coverage varies by state.

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