Secondhand smoke exposure and resting heart rate in young US adults: analysis of NHANES 2013-2018.

Background: Secondhand smoke (SHS) is a major cardiovascular risk factor, but its relationship with resting tachycardia, a marker of autonomic imbalance and adverse prognosis, remains unclear in young adults. Methods: We analyzed adults aged 18 to 40 years from the 2013-2018 National Health and Nutrition Examination Survey (NHANES). SHS exposure was defined as cotinine 0.05 to <10 ng/mL versus none (<0.05 ng/mL). The primary outcome was resting tachycardia ≥90 beats per minute (bpm) from standardized pulse measures; ≥100 bpm was examined in sensitivity analyses. Survey-weighted logistic regression estimated odds ratios (ORs) with sequential adjustment for clinical covariates. Results: The analytic sample included 4080 adults aged 18 to 40 years (representing ≈61.1 million US adults). Tachycardia prevalence was 9.98% (95% confidence interval [CI], 8.48-11.48) without detectable SHS and 9.05% (95% CI, 6.61-11.49) with SHS. SHS was not associated with tachycardia in unadjusted (OR 1.06, 95% CI 0.78-1.44), demographic-adjusted (OR 1.00, 95% CI 0.73-1.38), or fully adjusted models (OR 0.89, 95% CI 0.63-1.27), with consistent findings across age, sex, and race/ethnicity subgroups. In sensitivity analyses modeling cotinine continuously using restricted cubic splines within the detectable range (0.05-<10 ng/mL; n = 1382), there was no evidence of nonlinearity ( Conclusions: Among US adults aged 18 to 40, SHS exposure was not associated with resting tachycardia, although its broader cardiovascular risks remain substantial.