In diurnal animals, a longer melatonin signal is generally associated with a more depressed state of systems including reproduction, metabolism, and mood.

“The longer the melatonin signal, the more depressed not necessarily clinically depressed, although that can happen but the more depressed our systems tend to be. Reproduction, metabolism, mood, turnover rates of skin cells and hair cells all tend to be diminished compared to the spring and summer months for some Northern hemisphere, spring and summer months, or the times in which days are very long.”