Additionally, VKM cannot conclude on the safety of continuous use of 1 mg/day of melatonin for three months for adults.

Melatonin is a hormone produced in the body. Melatonin displays a marked circadian rhythm, with high levels at night and low levels during the day. Melatonin secretion increases soon after the onset of darkness, peaks in the middle of the night (between 2 and 4 am), and gradually falls during the second half of the night.

Orally ingested melatonin is efficiently and almost completely absorbed from the gastrointestinal tract. A single melatonin dose of 3 mg is expected to result in a maximum plasma concentration ranging 34-340 times higher than the melatonin level produced by the body.

The risk assessment was based on existing melatonin evaluations and one randomised controlled trial identified in a literature search. Only to a small degree did three of the reports include a quality evaluation of the included studies, therefore, VKM deemed all studies equally important. In clinical studies side effects were reported, including headache, nausea, and drowsiness. The delay of puberty was identified as an important potential risk, and reports of increased risk of seizures and autoimmune reactions caused concern. Further, immunocompromised patients and patients with renal or hepatic impairment should be cautious when using melatonin. Following melatonin exposure, several potential adverse effects, mainly endocrine effects, were evident.

Data on the use of melatonin during pregnancy and lactation, data on long-term safety in children (>2 years), and data on fertility effects were lacking.

Conclusions

“VKM cannot conclude on the safety of a daily intake of 0.2 mg melatonin for 3- to 6-year-olds, 0.3 mg melatonin for 7- to 10-year-olds, and 0.5 mg melatonin for 11- to 18-year-olds,” says Camilla Svendsen, scientific leader of the project group.

Svendsen points out that inconclusion is based on the lack of evidence both from high-quality animal experiments and from long-term studies on pubertal development in children and adolescents. She adds “Regarding adult use of melatonin, VKM cannot conclude on the safety of continuous use of 1 mg/day in a three month period.”

The risk assessment is part of VKM's new assignment on "other substances" from the Norwegian Food Safety Authority. A protocol for the risk assessment of these substances is published.