Adults with insomnia have been shown to have lower melatonin levels. Frequent travelers and shift workers are also likely to benefit from melatonin for the resynchronization of their sleep schedules, though a melatonin "deficiency" as such does not exist for these people. Patients with heart disease have been reported to have low melatonin levels, but whether this abnormality increases the risk of heart disease or whether heart disease leads to the low melatonin level is not yet known. People with schizophrenia were found to have low melatonin output and experienced significantly improved sleep following melatonin replacement supplementation.
Adeficient production of melatonin can result in anxiety and mood disorders, lowered basal body temperature insomnia, elevated estrogen/progesterone ratio, and immune suppression associated with cancer.