Smoking can take a toll on cognitive function

Smoking has long been known to be associated with a host of health problems—including lung cancer, heart disease, and chronic obstructive pulmonary disease—and now a recent study names one more: cognitive decline.

Data from the 2019 Behavioral Risk Factor Surveillance System (BRFSS) survey showed that current smokers had the highest prevalence of subjective cognitive decline (SCD), being about 1.9 times greater than never smokers (adjusted prevalence ratio [aPR], 1.87, 95 percent confidence interval [CI], 1.54–2.28). [J Alzheimers Dis 2022;doi:10.3233/JAD-220501]

Meanwhile, recent former smokers (those who had quit <10 years ago) and remote former smokers (those who had quit >10 years ago) had a prevalence of SCD that was 1.47 (95 percent CI, 1.02–2.12) and 1.11 (95 percent CI, 0.93–1.33) times greater than those who had never smoked.

“The association we saw was most significant in the 45–59[-year] age group, suggesting that quitting at that stage of life may have a benefit for cognitive health,” added senior study author Dr Jeffrey Wing, assistant professor of epidemiology at Ohio State University in Columbus, Ohio, US.

Wing further noted that that there was no significant difference in cognition between smokers and never smokers in the oldest group in the study, indicating that quitting earlier potentially confers greater benefits.

The BRFSS survey included a total of 136,018 respondents aged 45 to ≥80 years that met the study eligibility criteria. More than half of these respondents were never smokers (55.0 percent), female (53.6 percent), and non-Hispanic White (74.2 percent).

SCD was identified in 10.8 percent of the respondents. More than half of this group reported having hypertension (61.0 percent), and just over a quarter reported having diabetes (28.9 percent).

The association between smoking and SCD did not differ by sex at birth (p=0.73 for interaction).

Quitting and its effect on cognition

SCD refers to cognitive function deterioration that is attributed to the self-reported increase in the frequency of memory loss or confusion. This condition may be manifested as an early sign of mild cognitive impairment, Alzheimer’s disease, and other related dementias. [Neurology 2013;80:1778-1783; https://www.cdc.gov/aging/healthybrain/roadmap.htm]  

Wing and colleagues believe that evaluating SCD as a midstream marker of cognitive decline facilitates consideration of the possible effects of interventions at younger ages on the future risk of objective cognitive function. [Alzheimers Dement 2021;7:e12142]

“In our study, the dose-response relation between levels of smoking status and SCD implies that time since cessation may be linked to cognitive outcomes. Thus, our findings raise the question as to whether smoking cessation interventions in middle adulthood could have measurable impacts on future cognitive status,” they pointed out.

“Future longitudinal studies are necessary to address this question, as temporality cannot be assessed using measures of a cross-sectional nature, such as SCD. However, our findings underline the role that population-based measures like SCD play in the early detection of cognitive decline to inform further research and interventions that could mitigate the future population-level burden of cognitive disorders,” Wing and colleagues said.

Lead study author Jenna Rajczyk, a doctoral student of epidemiology at Ohio State University, said that the piece of evidence from the current study points to another reason to quit smoking—that it not only benefits respiratory and cardiovascular health but also preserves neurological health.