Seasonal affective disorder, or SAD, is depression that arrives and lifts at the same time each year, usually starting in autumn and easing in spring. It is not a separate illness; ICD-11 and DSM-5 record it as a seasonal pattern applied to repeated depressive episodes.
Key points
- Seasonal affective disorder is not a separate diagnosis; it is a seasonal pattern attached to repeated depressive episodes.
- Winter episodes carry atypical features: longer sleep, more eating with carbohydrate cravings, weight gain and heavy limbs.
- Around 3% of UK adults are thought to be affected at a clinically significant level.
- NG222 treats seasonal episodes as depression, and advises that the evidence for light therapy is uncertain.
- Light therapy is widely used and many find it helps, but it is rarely NHS funded and the trials are few and small.
Symptoms
- Low mood on most days over weeks, loss of interest, guilt, hopelessness, irritability or poor concentration.
- Sleeping longer than usual, daytime sleepiness, a heavy leaden feeling in the arms and legs.
- Eating more, with cravings for carbohydrate and sweet food, and weight gain over winter.
Causes and risk factors
- Reduced winter daylight is the leading explanation: changes in melatonin, reduced serotonin activity, a shift in the body clock.
- Risk is higher further from the equator, in women, where there is a family history of mental illness.
- Low vitamin D is often blamed, but supplementing it has not been shown to treat seasonal depression.
Treatment
- Same options as depression generally: guided self-help, group CBT, group exercise, SSRIs and counselling for less severe episodes.
- Light therapy (10,000 lux lamps, used for about 30 minutes each morning) is widely used, but NICE says the evidence for its efficacy is uncertain.
- CBT adapted for seasonal depression showed fewer recurrences than light therapy by the second winter in one trial.
When to speak to a professional
- Low mood has lasted most of the day, most days, for two weeks or more.
- Sleep, appetite or weight have changed noticeably over autumn or winter.
- The same pattern has returned in more than one year, or treatment is not helping.
If you need help now: Samaritans, call 116 123, free, 24/7. Shout, text SHOUT to 85258. NHS 111, then choose the mental health option. Call 999 if anyone is in immediate danger.