Juliette Massey-Smith wrote in the following query: I was wondering if you could help… I was re-reading about SAD in your AQA textbook and read on p.4 that in winter melatonin and serotonin are higher and this causes depression, but then also that LACK of serotonin causes it… What am I missing?

This error was corrected in the A2 Mini Companion (page 8): More darkness means more melatonin, and more melatonin means less serotonin (because melatonin is produced from serotonin). Low levels of serotonin are associated with depression.