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Impact of Cigarette Smoking and Its Interaction with Hypertension and Diabetes on Cognitive Function in Older Americans.

BACKGROUND
The detrimental impact of tobacco smoking on brain health is well recognized.


OBJECTIVE
To evaluate whether smoking acts synergistically with hypertension and diabetes to influence cognitive performance.


METHODS
We performed a cross-sectional analysis using the US National Health and Nutrition Examination Survey. Participants were tested for serum cotinine, a validated cigarette smoking/exposure biomarker, and had standardized blood pressure and hemoglobin A1c measurements. Participants were administered four cognitive tests: Digit Symbol Substitution (DSST), Animal Fluency, Immediate Recall, and Delayed Recall. Multivariable linear regression models adjusted for demographics and confounders evaluated the association of cotinine with cognition. Interaction testing evaluated effect modification by hypertension, diabetes, and their continuous measures (systolic blood pressure and hemoglobin A1c).


RESULTS
For 3,007 participants, mean age was 69.4 years; 54% were women. Using cotinine levels, 14.9% of participants were categorized as active smokers. Higher cotinine levels were associated with worse DSST performance when modeling cotinine as a continuous variable (β, -0.70; 95% CI, -1.11, -0.29; p <  0.01) and when categorizing participants as active smokers (β, -5.63; 95% CI, -9.70, -1.56; p <  0.01). Cotinine was not associated with fluency or memory. Effect modification by hypertension and diabetes were absent, except that cotinine was associated with worse Immediate Recall at lower blood pressures.


CONCLUSION
Higher levels of a smoking and secondhand exposure biomarker were associated with worse cognitive performance on a multidomain test. Overall, the relationship of cotinine with cognition was not contingent on or amplified by hypertension or diabetes; smoking is detrimental for brain health irrespective of these comorbidities.