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Feeling SAD?

Ever wondered what Seasonal Affective Disorder actually is? Or if it’s even a real thing? What causes it? Kate Mulcahy discusses sudden changes in hormones and light intensity to explain why winter makes us SAD.

It’s perfectly normal for people to gain energy and perk up at the beginning of summer as the appearance of the sun marks the end of a long winter. For some people, however, changing seasons can have such a huge impact on their mood that they are said to be suffering from Seasonal Affective Disorder, or SAD. SAD involves the effects of depression either developing or worsening during the wintertime and it is thought to be caused by the change in light intensity as the number of daylight hours decreases in the colder months. This is due to the change in the environment causing an imbalance in the hormones that control our mood. Different people react differently to this change, consequently there are the small amount of people that suffer from SAD. This could be partly due to our ancestors hibernating in winter months. But, not to worry; if it all gets too much, just move to Arizona, the sunniest place in the world.

This film is part of a series that provides the blueprint for a scientifically perfect summer. From sweating to hay fever, insects to jet lag, Kate helps us plan summer to perfection! The videos are a summer survival guide certified by science.

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Kurlansik, S.L. and Ibay, A. D. (2013) Seasonal Affective Disorder. Indian Journal of Clinical Practice. 24(7): 607-610 Revell, V.L. et al (2006) Advancing Human Circadian Rhythms with Afternoon Melatonin and Morning Intermittent Bright Light. The Journal of Clinical Endocrinology & Metabolism 91(1): 54-59

Wehr, T.A. (1997) Melatonin and Seasonal Rhythms. J Biol

Rhythms 12: 518-527


Vivacity by Kevin MacLeod (

Licensed under Creative Commons: By Attribution 3.0

Mining by Moonlight by Kevin MacLeod (

Licensed under Creative Commons: By Attribution 3.0


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