Seasonal Affective Disorder

What is seasonal affective disorder?

Seasonal affective disorder (SAD) is a form of depression that follows a seasonal pattern. Most commonly, symptoms begin in autumn or early winter and lift in spring. Less commonly, some people experience a summer pattern.

Winter SAD typically involves low mood, loss of interest in activities, fatigue, sleeping more than usual, increased appetite (particularly for carbohydrates), weight gain, and difficulty concentrating. These symptoms are significant enough to affect daily functioning and are not simply a preference for warmer weather or longer days.

SAD is thought to result from the effect of reduced daylight on the body’s internal clock (circadian rhythm), serotonin levels, and melatonin production. Prevalence varies by latitude - it is more common in northern regions where winter daylight hours are significantly reduced.

SAD and neurodivergence

ADHD and SAD

People with ADHD are approximately three times more likely to experience SAD than the general population - 9.9% compared to 3.3%. Research has also found that people with ADHD show significantly higher seasonal severity scores, meaning their mood and behaviour fluctuate more with the changing seasons.¹

The connection is rooted in circadian rhythm dysfunction, which is a feature of both conditions.

Shared circadian rhythm disruption

Both ADHD and SAD involve disruption to the body’s internal clock. People with ADHD commonly experience delayed sleep onset and a later chronotype - a biological tendency towards going to bed later and waking later. This circadian misalignment already causes difficulties with energy, mood, and cognitive function.

In winter, reduced natural light further disrupts circadian alignment. The combination of ADHD-related circadian delay and winter light reduction creates a compounding effect: the body clock drifts further out of sync with the demands of daily life, and both ADHD symptoms and mood deteriorate.

This can create a cycle: reduced winter light leads to poorer sleep, which worsens ADHD executive function and mood, which reduces motivation for physical activity and outdoor time, which further reduces light exposure.

Dopamine and light

Both SAD and ADHD involve dopamine dysregulation. Sunlight exposure is involved in dopamine production, so the reduced light of winter can worsen the dopamine dysfunction that ADHD already involves. This may partly explain why many people with ADHD describe a “winter crash” - a noticeable decline in motivation, focus, and mood that goes beyond typical seasonal variation.

Autism and seasonal changes

The research on autism and SAD specifically is limited, but there are several indirect connections worth noting.

Autistic people have heightened sensory sensitivity to light. Seasonal changes in light quality - from natural daylight to increased reliance on artificial lighting in winter - affect the sensory environment significantly. Fluorescent lighting, which many autistic people find distressing, becomes harder to avoid when natural light is scarce.

Both autism and ADHD involve circadian rhythm dysregulation, and poor sleep is extremely common across both conditions. The additional circadian disruption of winter may compound existing sleep difficulties.

Some autistic people may actually find certain aspects of winter easier - reduced social demands, quieter environments, and less sensory overwhelm from bright sunlight. The relationship between autism and seasonal mood changes is likely more complex and individual than a simple increase in depression.

Treatment

Light therapy

Light therapy is the most well-evidenced treatment specifically for SAD. It involves using a light box that produces 10,000 lux of light for 20-30 minutes each morning.

Light therapy works by resetting the circadian rhythm, improving serotonin function, and suppressing excessive melatonin production. For people with ADHD, morning light therapy may have the additional benefit of helping to correct the delayed sleep phase that ADHD produces.

Some studies suggest that light therapy may also improve ADHD symptoms directly - improving attention and reducing impulsivity - though this evidence is still emerging.

For autistic people, light sensitivity is an important consideration. Some people may find a 10,000 lux light box too intense. Options include starting at lower intensity and gradually increasing, using the light box at a greater distance, or trying dawn simulation alarm clocks (which gradually increase light over 30 minutes to mimic sunrise).

Circadian rhythm support

Consistent sleep-wake times - maintaining the same bedtime and wake time every day (including weekends) helps stabilise the circadian rhythm. This is particularly important for people with ADHD, whose circadian systems are already prone to drift.

Morning light exposure - getting outside within an hour of waking, even on cloudy days, provides enough natural light to support circadian alignment. Even a brief walk helps.

Evening light management - reducing exposure to bright and blue light in the evening (screens, overhead lighting) helps the body prepare for sleep.

Melatonin - for people with significant circadian delay, low-dose melatonin taken in the evening can help shift the body clock to an earlier schedule. This should be discussed with a GP or sleep specialist.

Medication

SSRIs are an effective treatment for SAD and can be started pre-emptively in autumn before symptoms develop. For people who already take SSRIs for depression or anxiety, the dose may need adjusting during winter.

ADHD stimulant medication should be continued during winter. Some people find that their stimulant feels less effective during the winter months - this may reflect the additional circadian and neurochemical burden of reduced light rather than a need to change medication.

Lifestyle approaches

Outdoor activity - combining physical exercise with natural light exposure addresses both the circadian and mood components of SAD. Even moderate outdoor activity during daylight hours can make a meaningful difference.

Vitamin D - supplementation during winter is widely recommended in the UK, where sun exposure is insufficient for adequate vitamin D production from October to March. While the evidence for vitamin D specifically treating SAD is mixed, deficiency is common and supplementation is low-risk.

Planning ahead - if you know you are vulnerable to winter depression, planning for it can help. Scheduling activities, social contact, and exercise in advance reduces the likelihood of withdrawal and isolation when motivation drops.

Further reading on neurobetter

• Mental health conditions - overview
• Depression
• ADHD
• Autism
• Self-help strategies

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