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.
The work will be presented this week at a neuropsychopharmacology conference.
The University of Copenhagen researchers who carried out the trial say their findings confirm what others have suspected - although they only studied 11 people with Sad and 23 healthy volunteers for comparison.
Using positron emission tomography (PET) brain scans, they were able to show significant summer-to-winter differences in the levels of the serotonin transporter (SERT) protein in Sad patients.
The Sad volunteers had higher levels of SERT in the winter months, corresponding to a greater removal of serotonin in winter, while the healthy volunteers did not.