Brain scans show cause of seasonal affective disorder

Scientists say they have identified the underlying reason why some people are prone to the winter blues, or seasonal affective disorder (SAD).

People with Sad have an unhelpful way of controlling the "happy" brain signalling compound serotonin during winter months, brain scans reveal.

As the nights draw in, production of a transporter protein ramps up in Sad, lowering available serotonin.

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