If you find yourself feeling sluggish and sad as the days get shorter you're not alone. About half of us report feeling less happy in winter. And for 5% of the population winter brings a serious depression. Seasonal Affective Disorder S.A.D. is the name for this spectrum of winter related mood disorder. It's thought to be largely due to the effect of reduced daylight hours on our internal biological rhythms. So how does it all work? And what can we do to prevent or treat the effects of S.A.D? Prof Anna Wirz-Justice is a world leading researcher in circadian rhythms, or chronobiology. Much of what we understand about the importance of sleep and light can be attributed to the research Anna carried out with her team at the Centre for Chronobiology, in Basel, Switzerland, where she is now Emeritus Professor of Psychiatric Neurobiology.
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