First, there is evidence that the suppression of melatonin secretion increases the risk of depression via its negative impact on sleep-wake rhythm, inhibitory effects on the secretion of monoamine neurotransmitters such as 5-HT and NE, and promoting effects on the secretion of inflammation-related cytokines such as TNF-α and IL-6 (46). Here, IL6 is linked to major depressive disorder.