A recent cross-sectional study examined the combined impact of secondhand smoke exposure and vitamin D deficiency on cognitive impairment among older adults.

in the study, published in Frontiers in Nutrition, investigators utilized data from the 2011 to 2014 National Health and Nutrition Examination Surveys (NHANES) to analyze 1,446 nonsmoking participants aged 60 years and older, assessing serum 25-hydroxyvitamin D levels, cotinine concentrations, and cognitive function test scores.

Cognitive impairment was defined as scoring in the lowest quartile on cognitive tests. The investigators employed multivariable logistic regression models to evaluate the potential synergistic effects of secondhand smoke exposure (SHS) and vitamin D (VDD) deficiency on cognitive impairment.

The findings revealed that VDD was independently associated with a nearly 60% increased risk of low scores on the Digit Symbol Substitution Test (DSST) (adjusted odds ratio [OR] = 1.62, 95% confidence interval [CI] = 1.03–2.53). While SHS exposure alone showed an association with cognitive impairment in crude models, significant synergistic effects with VDD were observed after adjusting for potential confounders. Specifically, the combined presence of SHS exposure and VDD was associated with more than triple the risk of low DSST scores (adjusted OR = 3.03, 95% CI = 1.57–5.83, P interaction = .001) and more than double the risk of impairment on the Animal Fluency Test (AFT) (adjusted OR = 2.40, 95% CI = 1.34–4.29, P interaction = .003).

Further stratified analyses indicated that the synergistic effect was more pronounced in participants with overweight and obesity. In those with obesity, the combined effect of SHS exposure and VDD on low DSST scores was particularly significant (adjusted OR = 4.73, 95% CI = 1.77–12.68, P interaction = .002). Similarly, those with overweight exhibited a notable combined effect on AFT impairment (adjusted OR = 5.30, 95% CI = 1.63–17.24, P interaction = .006).

"Our findings add new theoretical support for the potential risk factors of cognitive impairment due to living habits that can be modified," explained lead study author Yan Li, of the School of Public Health at Qingdao University in China, and colleagues.

The investigators suggested that further research is warranted to explore the mechanisms by which VDD and SHS exposure jointly contribute to cognitive impairment in older individuals.

No conflicts of interest were disclosed in the study.