Melatonin is a neurohormone produced by the pineal gland at the base of your brain. Its release is enhanced when you are in darkness and suppressed when you are exposed to bright light. By stimulating receptors in specific areas of your brain, melatonin helps establish your diurnal rhythm and determine your sleep cycles. The April 2011 issue of "Archives of Oral Biology" reports that melatonin also acts as an antioxidant, an anti-inflammatory, a stimulator of bone growth and an immune-regulating hormone.
According to "The Merck Manual of Diagnosis and Therapy," autoimmune disorders occur when your immune system produces antibodies that are directed against your own tissues. When these so-called autoantibodies attack your cells or tissues, they trigger an inflammatory response that can cause widespread damage. Components of this abnormal immune response include white blood cells and the inflammatory chemicals they produce, such as cytokines and prostaglandins.
Neuroendocrine Immune System
Your immune system is regulated by a multitude of internal and external forces. A 2009 review in "Arthritis Research and Therapy" states that an imbalance between your immune system and several of your hormones, such as vitamin D, melatonin, cortisol and sex hormones, is one of the primary driving forces behind a variety of diseases, including many autoimmune disorders. The interaction between your hormones and your immune system is called the neuroendocrine immune system, or NEI.
Among the various hormones involved in the NEI, some act to heighten your immune response, while others help to suppress it. Under normal circumstances, these opposing forces allow your immune system to efficiently address threats without causing injury to your own tissues. Cortisol and vitamin D have been shown to exert suppressing effects on the immune response, making them desirable agents for treating conditions where your immune system is overactive, such as autoimmune disorders.
In spite of melatonin's antioxidant properties, it has demonstrated a tendency to stimulate inflammation in patients with certain autoimmune disorders. A study published in the October 2007 issue of "British Journal of Clinical Pharmacology" demonstrated that rheumatoid arthritis actually worsened in study subjects who took melatonin. This finding both surprised and disappointed the study's authors, whose original hypothesis centered on the potential benefit from using melatonin to treat autoimmune diseases. However, these results mirrored those of other studies, which showed that melatonin stimulated immune cells to release inflammatory cytokines.
The interactions among immune cells, hormones and your nervous system -- the NEI -- are complex. Some previously observed properties of melatonin, such as its antioxidant activity, have not been borne out in all clinical studies. This has led some experts to recommend that you not use melatonin if you have an autoimmune disease, since it could aggravate your already overactive immune system and lead to a worsening of your symptoms.