Smoking and Dementia
It is not clear if there is an association between smoking and Alzheimer’s dementia. Smoking is a risk factor for vascular disease including atherosclerosis in the heart and brain. As a result, smoking will increase the risk of vascular dementia.
Components of cigarette smoke have been shown to damage the wall of blood vessels (vascular endothelium). This kind of damage is a precursor to the development of atherosclerosis. Smoking also changes blood flow by causing local clotting (thrombosis) and sudden constrictions in arteries (vasospasm).
Smoking substantially increases the risk of stroke, sudden death, heart attack, peripheral vascular disease, and aortic aneurysm. A study of British doctors found a strong relationship between the duration and extent of smoking and the death rate from heart disease among men younger than 65. Similarly, women who smoked 1-4 cigarettes per day had 2.5-fold greater risk of fatal and non-fatal heart attacks. Several large prospective population-based studies have also shown that individuals who smoked cigarettes are at increased risk of developing Alzheimer’s disease.
The increased risk of dementia is greatest in smokers without a hereditary propensity for dementia such as the APOE4 gene allele. Interestingly, this paradox may be explained by the increased risk of early death from cardiac disease of smokers with APOE4. (They may not live long enough to develop Alzheimer’s.) It is also possible that the APOE4 allele may create a protection from smoking risks.
The Rotterdam Study examined the relationship between dementia and Alzheimer’s disease in a cohort of individuals aged 55 years and older.  The study found an increased risk of dementia in both male and female smokers. The risk of dementia for current smokers was the highest. The mean age of onset for dementia was younger in former and current smokers than in those who never smoked. The total amount of pack-years smoked also correlated with increased dementia risk. Those who smoked 20 pack-years or more were three times more likely to develop Alzheimer’s compared to nonsmokers,. The risk for dementia in former smokers is only 1.5 times that of those never smoked. Despite some inconsistencies between studies, it’s clear that smoking damages the brain over time. The most reasonable way to protect the brain from dementia risk of smoking is stopping or never starting.
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