High cotinine levels as an associated factor with frailty status in older adults: evidence from the NHANES study

Smoking has been recognized as a contributing factor to frailty in older adults. Nevertheless, it remains uncertain whether the degree of smoking has a discernible impact on frailty among older smokers. This cross-sectional study was conducted to investigate the correlation between serum cotinine levels, a biomarker reflecting tobacco exposure, and the presence of frailty within a nationally representative cohort of older adults.

A total of 1626 individuals aged ≥ 60 who identified as smokers were included in the analysis. Participants were selected based on self-reported current smoking status. According to the Fried Phenotype, frailty is assessed through five dimensions: unintentional weight loss, slow walking speed, weakness, self-reported exhaustion, and low physical activity. Participants with three or more of these conditions were categorized as frailty, those with at least one but less than three as pre-frailty, and those with none as robust. Multinomial logistic regression models were employed to explore the relationship between serum cotinine level quartiles, with the lowest quartile as the reference group, and the various frailty statuses, with robustness as the reference category. These models were adjusted for covariates, including age, sex, race/ethnicity, alcohol drinking, daily protein intake, systolic blood pressure, serum albumin level, depressive symptoms, and cognitive function. The data used for this analysis were sourced from the National Health and Nutrition Examination Survey for the years 2011 to 2014.

The median age of the participants was 69.0 years. The majority were male (62.2%) and non-Hispanic White (49.0%). The distribution of frailty statuses among the participants revealed that the highest proportion had pre-frailty (50.7%), followed by robustness (41.1%), and frailty (8.2%). Multinomial logistic regression showed that participants in the 4^th quartile of serum cotinine level exhibited a higher probability of pre-frailty versus robustness (Odds ratio [OR] 1.599, 95% confidence interval [CI] 1.017, 2.513, P = 0.042). Participants in the 3^rd quartile of serum cotinine level had higher odds of frailty versus robustness (OR 2.403, 95% CI 1.125, 5.134, P = 0.024). Moreover, participants whose serum cotinine levels were higher than the literature cutoffs (≥ 15 ng/ml) were more likely to be pre-frail (Odds ratio [OR] 1.478, 95% confidence interval [CI] 1.017, 2.150, P = 0.035) or frail (Odds ratio [OR] 2.141, 95% confidence interval [CI] 1.054, 4.351, P = 0.041).

A higher serum cotinine level is linked to an elevated probability of pre-frailty and frailty among older smokers. Initiatives geared towards assisting older smokers in reducing or quitting their smoking habits might possibly play a crucial role in preventing pre-frailty and frailty.