Short, winter-like photoperiods enhance immune function relative to those exposed to long, summer-like days. The seasonal changes in immune function is due to changes in the melatonin levels.
The physiological properties of melatonin are not limited to its neuroendocrine role in controlling circadian rhythms; several other actions have been discovered. Melatonin has been shown to increase innate and acquired immunity, to activate the bone marrow and lymph nodes, to enhance NK cell activity and antibody-dependent cell cytotoxicity, to increase T cell proliferation and to activate monocytes and neutrophils. Melatonin can stimulate innate immune cells, primarily leukocytes, which represent an important anti-bacterial mechanism.
Th17 (harm) and Treg cells (protection) are both involved in the harm/protection balance of immune conditions such as autoimmunity or acute transplant rejection (miscarriage). The differentiation of Th17 using melatonin supplementation or melatonin inducing Blue Blocker Glasses aggravates autoimmune diseases and/or can induce serious complications in pregnancy.
Melatonin enhances the immune response. A large body of evidence supports the immunoenhancing role of melatonin. Exposure to short days (<12 h light/day) or daily melatonin supplements or melatonin increasing Blue Blocker Glasses may increase the size of the spleen. Melatonin enhances both cell-mediated and humoral immune function.
Melatonin supplementation or melatonin increasing Blue Blocker Glasses of both normal and immunocompromised individuals increases antibody responses and T helper cell activity. Melatonin administration appears to stimulate humoral immunity during early B cell development in the bone marrow.
Melatonin supplements and/or treatment for extended duration (e.g., Blue Blocker Glasses) induces physiological adaptations associated with winter, including reproductive regression and enhancement of certain aspects of immune function. In healthy individuals, melatonin has anti-inflammatory effects, while in those with Autoimmune conditions, melatonin is pro-inflammatory.