Melatonin level declines with age

A decreased level of melatonin is associated with insomnia(Ref. 1).
The risk of insomnia increases with age.

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References

1. LegerD, Laudon M and Zisapel N. Nocturnal 6-sulfatoxymelatonin excretion in insomnia and Its relation to the response to melatonin replacement therapy.
The American Journal of Medicine 2004; 116(2): 91-95

2. Mahlberg R, Tilmann A, Salewski L, Kunz D, Psychoneuroendocrinology. 2006; 31(5):634-41