How scientists are shining light on the biology behind seasonal affective disorder

Researchers tracking large cohorts are discovering the effects of sleep, light and therapy on people impacted by winter's arrival

For some, the darkening days of autumn bring more than the annual ritual of reviving woolly jumpers and turning on the central heating. As the evenings close in and the mornings grow murky, energy ebbs and a heavy sadness settles in.

Although seasonal affective disorder (Sad) was only formally recognised by psychiatrists in the 1980s, the link between the seasons, mood and vitality has long been observed.