, based on data from 3,660 individuals.
Previous research has shown an association between trace metals and sleep and sleep patterns, but data on the impact of serum trace metals on sleep disorders have been limited, wrote Ming-Gang Deng, MD, of Wuhan (China) University and colleagues.
In a study published in the Journal of Affective Disorders, the researchers reviewed data from the National Health and Nutrition Examination Survey (NHANES) 2011-2016 to calculate the odds ratios of sleep disorders and serum zinc (Zn), copper (Cu), and selenium (Se). The study population included adults aged 18 years and older, with an average age of 47.6 years. Approximately half of the participants were men, and the majority was non-Hispanic white. Serum Zn, Cu, and Se were identified at the Environmental Health Sciences Laboratory of the Centers for Disease Control and Prevention National Center for Environmental Health. The lower limits of detection for Zn, Cu, and Se were 2.9 mcg/dL, 2.5 mcg/dL, and 4.5 mcg/L, respectively. Sleep disorders were assessed based on self-reports of discussions with health professionals about sleep disorders, and via the Sleep Disorder Questionnaire.
After adjusting for sociodemographic, behavioral characteristics, and health characteristics, adults in the highest tertiles of serum Zn had a 30% reduced risk of sleep disorders, compared with those in the lowest tertiles of serum Zn (odds ratio, 0.70; P = .035). In measures of trace metals ratios, serum Zn/Cu and Zn/Se also were significantly associated with reduced risk of sleep disorders for individuals in the highest tertiles, compared with those in the lowest tertiles (OR, 0.62 and OR, 0.68, respectively).
However, serum Cu, Se and Cu/Se were not associated with sleep disorder risk.
Sociodemographic factors included age, sex, race, education level, family income level; behavioral characteristics included smoking, alcohol consumption, physical activity, and caffeine intake.
The researchers also used a restricted cubic spline model to examine the dose-response relationships between serum trace metals, serum trace metals ratios, and sleep disorders. In this analysis, higher levels of serum Zn, Zn/Cu, and Zn/Se were related to reduced risk of sleep disorders, while no significant association appeared between serum Cu, Se, or Cu/Se and sleep disorders risk.
The findings showing a lack of association between Se and sleep disorders were not consistent with previous studies, the researchers wrote in their discussion. Previous research has shown that a higher Se was less likely to be associated with trouble falling asleep, and has shown a potential treatment effect of Se on obstructive sleep apnea, they said.
“Although serum Cu and Se levels were not correlated to sleep disorders in our study, the Zn/Cu and Zn/Se may provide some novel insights,” they wrote. For example, Zn/Cu has been used as a predictor of several clinical complications related to an increased risk of sleep disorders including cardiovascular disease, cancer, and major depressive disorder, they noted.
The findings were limited by several factors including the cross-sectional design, use of self-reports, and the inability to examine relationships between trace metals and specific sleep disorder symptoms, such as restless legs syndrome, insomnia, and obstructive sleep apnea, the researchers noted.
However, the results were strengthened by the large national sample, and support data from previous studies, they said.
“The inverse associations of serum Zn, and Zn/Cu, Zn/Se with sleep disorders enlightened us that increasing Zn intake may be an excellent approach to prevent sleep disorders due to its benefits from these three aspects,” they concluded.
The study received no outside funding. The researchers had no financial conflicts to disclose.