Seasonal Affective Disorder: When the Seasons Change Your Brain

Every year, around the same time, something shifts. Energy drops. Motivation disappears. Sleep stretches longer than usual but leaves you feeling no more rested. The desire to withdraw, to hibernate, to simply wait it out until things change — all of this arrives on schedule.

Seasonal Affective Disorder (SAD) is a pattern of depression that is tied to seasonal change, most commonly the reduced daylight of autumn and winter.

The Biology

SAD appears to involve disruption to several light-sensitive biological systems. Melatonin production, which signals darkness and promotes sleep, is altered by reduced light exposure — people with SAD may have dysregulated melatonin timing. Serotonin, which is involved in mood regulation, is also affected by light; reduced light exposure appears to reduce serotonin activity.

Circadian rhythms — the biological clock that governs sleep, hormones, and mood — are also sensitive to light and can shift out of phase during winter months.

Recognising It

The diagnostic criterion for SAD is a pattern of depressive episodes that begin and end at the same time each year, for at least two consecutive years, with full remission between episodes.

Summer SAD (less common) involves a different symptom profile: insomnia, decreased appetite, agitation, and anxiety.

Treatment

Light therapy — daily exposure to a full-spectrum bright light box (at least 10,000 lux) for twenty to thirty minutes each morning — is a first-line treatment with strong evidence. Antidepressants (particularly SSRIs and bupropion) are also effective. Psychotherapy, particularly CBT adapted for SAD, addresses the behavioural patterns (withdrawal, reduced activity) that maintain the depression.

If you notice a predictable seasonal dip, you are not imagining it. And you do not have to simply endure it.