Is dementia really related to smoking?

Drugs
smoking and dementia

Researchers in Kentucky investigated if smoking truly does increase the risk of dementia, following other studies that have come to this conclusion.

A recent study published in the Journal of Alzheimer’s Disease examined if tobacco smoking was a risk for dementia. Numerous studies have demonstrated that smoking is associated with risk of dementia. However, these researchers discuss how previous results did not take into account the fact that smoking is a competing risk of death. This is important to consider since smoking is strongly associated with earlier death due to other medical conditions.

Smoking can be the cause of death before signs of dementia appear

The researchers studied how smoking is a competing risk for dementia, which is an event that either prevents the observation of dementia or alters the chance that dementia occurs. For example, the study discusses how smoking may kill someone before they show signs of dementia, therefore, it would be inaccurate to attribute the person’s dementia to smoking. As such, this study performed a mathematical analysis to determine if smoking can actually be accounted for when predicting dementia risk.

The study included 531 adults older than 60 years old who had normal brain function at the start of the study and were followed over time by the University of Kentucky’s Alzheimer’s disease Center. The participants were followed for about 11.5 years. Approximately 9% of the participants reported smoking tobacco at the beginning of the study, and about 43% reported being former tobacco smokers.

Researchers could not assume participants’ exposure to tobacco smoke

Since smoking was self-reported only at the beginning of the study, a limitation of this study is that the researchers cannot assume exactly how much exposure to tobacco smoke the participants had. For example, they could not take into account the fact that former smokers may have reinitiated smoking or current smokers may have increased the amount of smoking tobacco.

Furthermore, the study did not collect data on secondhand smoke exposure, diet, and physical activity which are all factors that can contribute to the risk of dementia. Lastly, this study was only done in a group of participants specific to the university that was conducting the study and cannot be inferred to the entire population.

Smokers at the start of the study had an increased risk of death without dementia

About 20% of the participants were diagnosed with dementia at the end of the study, and about 45% of the participants passed away without dementia before the study ended. The researchers also found that their statistical model that accounts for the competing risk of death without dementia found a similar risk for both current and former smokers.

However, participants who were current smokers at the beginning of the study were found to have an increased risk of death without dementia. After adjusting for the competing risk of death without dementia, smoking was not found to be associated with incident dementia and can be supported by neuropathology on 302 of the participants.

The concept of competing risk is relatively complicated and can change how data is accounted for in a study and ultimately change study conclusions. Therefore, it is necessary to consider competing risk when analyzing causality in studies that examine how a particular habit can affect health outcomes.

Study did not find an association between smoking and dementia risk

Contrary to previous studies, this study did not find that smoking was associated with dementia risk because the researchers took into account other factors that could lead to death in the participants that were studied which could be attributed to smoking but not necessarily increased risk of dementia.

The authors encourage future dementia research to focus on factors other than smoking to prevent dementia risk, as well as the need to incorporate methods to account for competing risk when performing similar studies in the future.

Written by Tatsiana Verstak, M.S., B.S.

Reference: Abner, E. et al. Tobacco Smoking and Dementia in a Kentucky Cohort: A Competing Risk Analysis. Journal of Alzheimer’s Disease. 68 (2019) 625–633.

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