Even though various studies have been conducted to investigate the relationship between trace metals and sleep, few epidemiological studies have evaluated the relationship between trace metals and sleep disorders in American adults.
This study intended to evaluate the associations of serum zinc (Zn), copper (Cu), selenium (Se), Zn/Cu, Zn/Se, and Cu/Se ratios with sleep disorders in American adults.
We conducted a cross-sectional analysis of 3660 adults aged ≥18 years old who participated in the National Health and Nutrition Examination Survey (NHANES) 2011–2016. Binary logistic regression was employed to calculate the odds ratio (OR) and 95 % confidence interval (CI) of either serum trace metals or serum trace metals ratios with risks among sleep disorder phenotypes. The restricted cubic spline (RCS) model was additionally utilized to check the dose-response relationships between serum trace metals, serum trace metals ratios, and sleep disorders.
Logistic regression demonstrated that higher serum Zn (OR: 0.70, 95 % CI: 0.51–0.97, p = 0.035), Zn/Cu (OR: 0.62, 95 % CI: 0.45–0.87, p = 0.007), and Zn/Se (OR: 0.68, 95 % CI: 0.49–0.95, p = 0.025) were related to a decreased likelihood of self-reported sleep disorders, and dose-response relationships were detected by the RCS models, after adjustment for sociodemographic, behavioral, and health characteristics. No associations between serum Cu, Se, Cu/Se, and sleep disorders were observed. The findings in the sensitivity analyses were consistent with these results.
Our study revealed that serum Zn, Zn/Cu, and Zn/Se were inversely associated with the risk of self-reported sleep disorders in US adults.
Healthy/normal sleep patterns, often evaluated by healthy sleep scores, are characterized as early chronotype, sleep 7–8 h per day, reported never or rare insomnia symptoms, no self-reported snoring, and no frequent daytime sleepiness (Fan et al., 2020; Li et al., 2021). Sleep disorders, including insomnia, sleep apnea, narcolepsy, and restless leg syndrome, are one of the most common clinical problems which disturb sleep patterns (Karna and Gupta, 2022). Besides the direct negative influence on enthusiasm and mental state, sleep disorders have been reported to be associated with various adverse health outcomes, such as obesity, hypertension, type 2 diabetes, cardiovascular disease, and increased mortality (Huyett et al., 2021; Kase et al., 2021; Medic et al., 2017). Moreover, the prevalence of sleep disorders has been rising in the past decades and peaked at a high level, for instance, a recent study revealed that the prevalence of sleep disorders in American adults was 27.1 % (Kase et al., 2021). Since the high prevalence and correlation with various adverse health outcomes, exploring the risk factors of sleep disorders is of vital significance.
The baseline characteristics of participants across survey waves were presented in Table 1. The overall prevalence of self-reported sleep disorder was 28.9 % and showed a slightly climbing trend from 27.6 % in 2011–2012 to 29.9 % in 2015–2016, but without statistical significance (p = 0.610). The distributions of serum trace metals and serum trace metals ratios across three cycles did not significantly alter.
Characteristics of participants with and without self-reported sleep disorders were presented in Table 2. From the perspective of univariate analysis, education level, family income, physical activity, caffeine intake, serum Zn, serum Cu, serum Se, and serum Zn/Se were not related to the prevalence of sleep disorders. Advanced age, female gender, nonHispanic white race, smoking, drinking, obesity, hypertension, diabetes, depression, lower Zn/Cu, and higher Cu/Se were likely to be risk factors for sleep disorders in American adults.
The results of binary logistic regression models of serum trace metals and serum trace metals ratios on self-reported sleep disorders were described in Table 3. After fully adjusted for sociodemographic, behavioral, and health covariates, serum Cu and serum Se were not related to the risk of sleep disorders in American adults. However, compared to individuals in the lowest tertiles of serum Zn (<Q1), adults with the highest tertiles of serum Zn (>Q3) had a 30.0 % (OR: 0.70, 95 % CI: 0.51–0.97, p = 0.035) lower risk to report sleep disorders.