Seasonal Affective Disorder (and how it shows up at work)

Let’s get specific for a minute – because the phrase “seasonal slump” does a lot of heavy lifting it does not deserve. Seasonal Affective Disorder (SAD) is a form of recurrent depression linked to predictable seasonal changes, most commonly winter – but not exclusively.¹

Some people experience summer-pattern SAD, where symptoms show up as daylight increases and routines shift.²

So no, this is not about people “struggling with motivation” or “needing a better morning routine”. It’s a biological response to environmental change, which means if we manage it like a vibes issue, we’re already off track.

So what’s happening in our bodies? Let's talk science.

SAD is linked to disruptions in the body’s "circadian rhythm" – your internal clock that regulates sleep, mood, energy, attention, and basically whether your brain is cooperating today.³

Seasonal changes affect:

• Light exposure, which alters melatonin production (the hormone that controls sleep)⁴

• Serotonin activity, which plays a key role in mood regulation and emotional stability⁵

• Sleep–wake cycles, especially when daylight shifts quickly or heat interferes with rest⁶

In winter-pattern SAD, reduced daylight can increase melatonin and reduce serotonin.

In summer-pattern SAD, extended daylight and heat can suppress melatonin too much, disrupt sleep, and increase agitation or anxiety.²

Brains and bodies respond differently to seasonal shifts – and for some people, those responses genuinely impair functioning. This is not fragility, or lack of resilience, it's biology doing what biology does.

What does this look like at work?

For employees, SAD may show up as:

• Fatigue or poor concentration

• Irritability, agitation, or withdrawal

• Sleep disruption affecting reliability or focus

• A noticeable change in mood or performance that doesn’t match workload or capability

Here’s the important bit for managers: this often appears as “performance issues” before it becomes a wellbeing conversation.⁷ By the time someone discloses distress, they may already be anxious about being seen as unreliable, inconsistent, or “not coping”. That's harmful for them, and for the organisation.

Evidence-based management - let's make it practical

"Seasonally informed" managers:

• Notice patterns without diagnosing or moralising (“I’ve noticed a change – how are things feeling?”)⁸

• Offer flexibility around hours, location, or workload when sleep and energy are disrupted⁹

• Avoid seasonal productivity myths – longer days do not magically increase human capacity¹⁰, particularly for those with summer-pattern SAD

• Intervene early with support, not late with performance sanctions

• Make support routes visible and psychologically safe, without requiring people to self-label or disclose diagnoses¹¹

You don’t need to be a clinician. You do need to manage with the understanding that human capacity is not static or season-neutral. If your management approach only works when people feel fine, that’s not resilient leadership – it’s conditional.

And humans are, inconveniently, not condition-free.

The bit I want you to sit with

Seasonal change is predictable and distress is not a personal failure. Your response as a manager materially shapes wellbeing, retention, and performance - that’s not “extra care”, that’s evidence-based leadership.

If this was useful, feel free to forward it to a manager who still thinks SAD is solved by “getting outside more” 👀

References

(For all you lovable nerds)

1. Rosenthal, N. E. et al. (1984). Seasonal affective disorder: A description of the syndrome and preliminary findings. Archives of General Psychiatry.

2. Wehr, T. A. et al. (2001). Seasonality in mood and behavior: Summer versus winter depression. American Journal of Psychiatry.

3. Wirz-Justice, A. (2009). Seasonal affective disorder: An overview. Chronobiology International.

4. Lewy, A. J. et al. (2006). The circadian basis of winter depression. Proceedings of the National Academy of Sciences.

5. Lambert, G. W. et al. (2002). Effect of sunlight and season on serotonin turnover in the brain. The Lancet.

6. Crowley, S. J. & Eastman, C. I. (2018). Human circadian rhythms and sleep. Sleep Medicine Clinics.

7. Johns, G. (2006). The essential impact of context on organizational behavior. Academy of Management Review.

8. ACAS (2023). Managing mental health at work.

9. CIPD (2022). Flexible working and employee wellbeing.

10. Pencavel, J. (2015). The productivity of working hours. Economic Journal.

11. Edmondson, A. (2018). The Fearless Organization. Wiley.