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The science

Winter sun: what the light really does

In December and January Marrakech and Agadir get about 7 hours of sun a day, against under 2 in London. At their latitude winter sunlight can still make vitamin D in skin; in London, Paris or Boston it cannot. Whether a week of it changes your mood has not been tested.

Evidence: Moderate

The sunlight and vitamin D chemistry is strong; the links between daylight and mood are large studies, but associations only.

What the studies show

In a classic 1988 study, winter sunlight in Boston (42°N) made no vitamin D precursor in skin from November to February, and in Edmonton (52°N) from October to March. At 34°N it still did in midwinter. Marrakech (31.6°N) and Agadir (30.4°N) are south of that line.

Bright light therapy is an evidence-based treatment for winter depression (seasonal affective disorder). A 2020 meta-analysis of 19 trials found a real but modest effect, smaller than older estimates. These are trials of light boxes, used every morning, not of holidays.

In over 85,000 UK adults who wore light sensors for a week, more daytime light went with lower risk of depression and other mental health problems, and more light at night with higher risk. That is an association; people who feel unwell may simply go out less.

Vitamin D pills have not been shown to prevent depression: a trial of 18,353 adults over five years found no effect, and meta-analyses find at most a small one.

In Morocco

December to February, Marrakech has highs around 19–21 °C and Agadir 21–22 °C, with clear skies most days. The nights are cold, in the desert near freezing, and many riads are not heated: pack a warm layer.

UV in winter is moderate at midday, but pale winter skin, the High Atlas (UV rises with altitude) and reflection from sand add up. Shade at midday and sunscreen, especially from February.

Where it stops

  • No study has tested whether a winter trip to Morocco treats or prevents winter depression. If you have it, the treatment with evidence is light therapy, with your doctor.
  • Vitamin D made in skin depends on skin type, how much skin is uncovered, time of day and sunscreen. A short trip will not fix a deficiency, and the 1988 study measured skin chemistry, not blood levels.
  • Studies disagree on how much latitude matters for winter depression: a 1999 review found little link, a 2025 meta-analysis found more of it further north.
Sources, checked 2026-11-14
  1. Webb, Kline & Holick (1988). Influence of season and latitude on the cutaneous synthesis of vitamin D3. Journal of Clinical Endocrinology and Metabolism 67(2)
  2. Pjrek et al. (2020). The efficacy of light therapy in the treatment of seasonal affective disorder: a meta-analysis of randomized controlled trials. Psychotherapy and Psychosomatics 89(1)
  3. Golden et al. (2005). The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence. American Journal of Psychiatry 162(4)
  4. Burns et al. (2023). Day and night light exposure are associated with psychiatric disorders: an objective light study in >85,000 people. Nature Mental Health 1
  5. Okereke et al. (2020). Effect of long-term vitamin D3 supplementation vs placebo on risk of depression (VITAL-DEP). JAMA 324(5)
  6. Mersch et al. (1999). Seasonal affective disorder and latitude: a review of the literature. Journal of Affective Disorders 53(1)
  7. Kim et al. (2025). Global prevalence of seasonal affective disorder by latitude: a systematic review and meta-analysis. Journal of Affective Disorders 390
  8. Sunshine hours: Marrakech (NOAA normals 1981–2010) and Agadir (NOAA 1991–2020), via Wikipedia climate tables
  9. Sunshine hours: London, Kew (Met Office 1991–2020)

More of the science

Holidays and happinessThe lift is real, small and short. Looking forward to it counts too.New places and memoryVaried days go with better mood; routine shrinks remembered time.Awe in the dunesAwe is a well-studied emotion. Vast places reliably trigger it.The Milky WayMost Europeans can't see it from home. In the Sahara you can.The sea, and surfingCoast visits go with feeling better. Surf therapy: too early to say.Walking in the AtlasA walk in nature lifts mood for hours. Toubkal also means altitude.The hammamNo study has tested it. What sauna research does and doesn't say.Tea with strangersTalking to strangers feels better than people expect. Sharing food builds trust.Other cultures and creativityLiving abroad is linked to creativity. A short trip wasn't.A few words of DarijaNo proven brain boost. Still the best way to start a conversation.Couples and familiesNew things together help in the short term. A trip won't fix a relationship.

Plan it

MarrakechWinter days in the red cityAgadir and TaghazoutThe warmest winter coastWhen to goMonth by month: weather and Ramadan

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