Associations of Zinc and Copper Levels in Serum and Hair with Sleep Duration in Adult Women

Zinc (Zn) and copper (Cu) are essential micronutrients involved in numerous metabolic reactions. They are also antagonists of the N-methyl-d-aspartate glutamate (NMDA) receptor in the central nervous system, which mediates mood, cognition, pain perception, and sleep. However, there have been few studies on the effects of Zn and Cu on sleep. A total of 126 adult women were recruited in this cross-sectional study. Zn and Cu levels in the serum and hair were measured for each subject. The participants completed the 7-day physical activity recall questionnaire and the Hospital Anxiety and Depression Scale. The mean hours of sleep were compared according to the tertiles of Zn, Cu, and Zn/Cu ratio in the serum and hair by analyses of covariance. The participants in the middle tertile of Zn and Zn/Cu ratio in the serum had significantly longer sleep duration compared to those in the lowest tertile (p < 0.05 for each). An increasing Zn/Cu ratio in the hair was associated with longer sleep hours (p = 0.026), whereas sleep duration decreased significantly from the lowest to the highest tertile of hair Cu level (p = 0.010). The largest percentage of participants with optimal sleep duration was observed in the highest tertile of Zn/Cu ratio in the serum and hair (p = 0.052 and 0.046, respectively). The results of our study suggest that Zn/Cu ratio as well as Zn or Cu levels in the serum and hair may be involved in sleep duration in adult women.