A US study reveals Sad may be associated with a genetic mutation in the eyes, a revelation that could lead to more effective treatments for the disorder.
Ignacio Provencio from the University of Virginia explained melanopsin, a photopigment gene in the eye, could play a role in causing seasonal affective disorder (Sad) in people with a recently discovered mutation.
"While a person diagnosed with Sad does not necessarily carry the melanopsin mutation, what we found strongly indicates that people who carry the mutation could very well be diagnosed with Sad," he said.
The study suggested the genetic mutation in the eye makes someone with Sad less sensitive to light.
This means the light quality in the winter months may not be enough for them to be able to function normally.
Sad.org.uk says the disorder affects around two million people in the UK.
Symptoms include extreme fatigue, sleep problems, loss of sex drive, anxiety, depression and carbohydrate or sweet food cravings.
by Adrian Galbreth