I'm reading this Wikipedia article on light therapy and noticed a peculiar statement:

The production of the hormone melatonin, a sleep regulator, is inhibited by light and permitted by darkness as registered by photosensitive ganglion cells in the retina. To some degree, the reverse is true for serotonin, which has been linked to mood disorders.

If I read this correctly, when melatonin is suppressed, serotonin is released? This makes some sense. I'm interested if there is any scientific backing to serotonin being affected by light levels.

  • $\begingroup$ You might want to look into seasonal affective disorder which is possibly related to this. $\endgroup$
    – Rory M
    Dec 21, 2012 at 15:59

1 Answer 1


I'm not sure about humans, but this is true of many vertebrate's retinas. There is experimental evidence showing light-inhibited production of serotonin. This article reviews how serotonin is regulated in response to day lenght (as well as fasting/feeding cycles). The authors suggest a mechanism in which serotonin and ghrelin integrate signals from fasting/feeding and night/day together.

  1. Nowak JZ, Z Urawska E, Zawilska J. Melatonin and its generating system in vertebrate retina: circadian rhythm, effect of environmental lighting and interaction with dopamine. Neurochem Int. 1989;14(4):397-406.

  2. Kirsz K, Zieba DA. A review on the effect of the photoperiod and melatonin on interactions between ghrelin and serotonin. Gen Comp Endocrinol. 2012 Nov 1;179(2):248-53. doi: 10.1016/j.ygcen.2012.08.025. Epub 2012 Sep 5.

  • $\begingroup$ The second article looks really nice. Is there a place where I can take a look at it for free? $\endgroup$
    – Alex Stone
    Dec 27, 2012 at 19:18
  • $\begingroup$ No, but if you give me your email I can send you a PDF. $\endgroup$
    – user560
    Dec 28, 2012 at 1:44

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