Linked to immune decline
Melatonin is a naturally occurring hormone which, in a normal person, has its source in the thymus gland. Melatonin secretion declines steadily throughout life. Melatonin decline occurring in old age correlates with and appears causally related to the immune decline of old age. Melatonin decline is clearly not the only cause of the loss of immune surveillance in old age, but the decline in melatonin appears to contribute significantly.
Melatonin is intimately related to sleep, NK cell function, and emotional state. There are hundreds of research papers in the scientific literature related to the effect of melatonin on immunity and cancer.
Reports in the Italian medical literature suggest melatonin and IL-2 are synergistic if given together at or around early sleep. A beneficial consequence of this synergy is that IL-2 benefits may be seen at sufficiently low doses of this expensive cytokine to be more easily affordable by cancer victims.