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The Darkening Days: Uncovering the Science Behind Seasonal Affective Disorder

Strategic Insights

— 2 min read

As the seasons change, many of us experience a collective sadness that can be difficult to shake. For some, the longer nights and colder days trigger a deeper melancholy, known as seasonal affective disorder (SAD). While SAD was formally recognized by psychiatrists in the 1980s, the link between the seasons, mood, and vitality has been observed for centuries. Chinese texts, such as the Yellow Emperor's Classic of Medicine, dating back to around 300 BC, describe how the seasons affect all living things. Today, scientists are rediscovering the intricate relationship between our biology and the seasons, and are working to understand the triggers and treatments for SAD.

Key Takeaways:

  • SAD affects approximately 1 in 5 people in the UK, with about 2% experiencing full SAD.
  • The triggers of SAD changes are still being investigated, but are almost certainly linked to reduced daylight.
  • Light is the key regulator of our internal body or circadian clock, influencing the timing of hormone release, alertness, and mood.
  • People with bipolar disorder may be very sensitive to light and seasonal cues, and that's triggering their symptoms.
  • Researchers have found fluctuations in the expression of more than 4,000 protein-coding genes in white blood cells and fat, along with changes in the cellular composition of blood itself across the year.
  • The most effective antidote to the winter slump is light, with bright light therapy remaining the gold standard for treating SAD.
  • Natural sunlight is a powerful substitute for bright light therapy, with studies showing that Amish communities in the US, who spend more time outdoors and less time exposed to bright artificial light at night, have some of the lowest SAD rates recorded among Caucasian populations.
  • Cognitive behavioural therapy tailored for SAD can be as effective as light therapy, helping people reframe their relationship with winter rather than just manage symptoms.

Statistics:

  • 1 in 5 people in the UK experience a milder seasonal dip in mood, known as subsyndromal SAD or "the winter blues."
  • About 2% of the population experiences full SAD.
  • New York has a SAD prevalence of about 4.7%.
  • The expression of over 4,000 protein-coding genes in white blood cells and fat fluctuates across the year.
  • Daylight resets the circadian clock and suppresses melatonin, with early morning light being especially powerful.

Sources:

  • Yellow Emperor's Classic of Medicine
  • UK Biobank
  • University of Edinburgh, under Cathy Wyse
  • British Sleep Society conference in Brighton next week
  • Mind charity (0300 123 3393)
  • Childline (0800 1111)
  • Mental Health America (988 or 988lifeline.org)
  • Beyond Blue (1300 22 4636)
  • Lifeline (13 11 14)
  • MensLine (1300 789 978)

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