On the twenty-first of December the sun rises over Riga at nine in the morning and sets at 15:43. In between it never climbs more than ten degrees above the horizon, about the width of a fist held at arm's length. That is 6 hours and 43 minutes of day, against 17 hours and 53 minutes at midsummer. Vilnius gets 7 hours and 14 minutes, Tallinn 6 hours and 3 minutes, Helsinki 5 hours and 49 minutes. In Riga, from 22 November until 6 January, the sun is down before four in the afternoon.

You know the moment. You look up from the screen and the window has turned into a mirror: your own face, the desk lamp, the room behind you, and beyond the glass nothing at all. It is four o'clock. There are six hours of the day still to live, and your body has just been told that it is night.

We live at the latitude of southern Alaska, warmed by an ocean current into somewhere mild enough to forget how far north we are. The light does not forget. This is an article about what the dark months do to a body, and about the things that have been shown to help: a walk, a window, a lamp, a vitamin, and colour on the table.

The clock behind your eyes

Until 2002, any textbook would have told you that the eye has two kinds of light sensor, rods and cones. That year a third was demonstrated: a small population of ganglion cells in the retina that respond to light on their own, even when every signal from the rods and cones is blocked, and that are wired straight to the suprachiasmatic nucleus, the brain's master clock [1]. These cells do not make pictures. They measure brightness, and they tell the clock what time it is.

They are not impressed by indoor lighting. Direct sunlight reaches 100,000 lux and full daylight about 25,000, while standard office lighting is around 500 lux and often lower [2]. To the clock, a well-lit office is one fiftieth of an ordinary day outdoors.

What that difference does was measured in the Rocky Mountains. Eight people wore light sensors through a week of normal electrically lit life, then through a week of camping with nothing but sun and campfire. At home they averaged 979 lux across their waking hours; in tents, 4,487 lux, more than four times as much. Every marker of their internal clock moved about two hours earlier, until the evening rise of melatonin sat close to sunset [3]. The same laboratory then repeated the experiment at the winter solstice. Five people spent 6 days camping in December, received more than 13 times the light they got at home, and their melatonin onset moved 2.6 hours earlier [4].

Read that once more. In midwinter, the short natural day gave people thirteen times more light than their heated, wired, modern one. That is the Baltic light deficit in a sentence: the trouble is less that the day is short than that we spend the short day behind glass, and then light the long evening brightly enough to confuse the clock and too dimly to set it.

What four o'clock does to the brain

A clock that gets no clear signal in the morning drifts late, and the alarm then catches the body still in its biological night. The winter campers showed what the body would prefer: left to natural light, the nightly stretch of melatonin lengthened to 14.4 hours, against 10.0 hours in summer [4]. Given the chance, a human being keeps a winter schedule. The office calendar does not give it the chance, and the gap between the two is the particular heaviness of a December morning.

Light also reaches mood more directly. In 2002 researchers took blood from the jugular veins of 101 healthy men at different times of year, to measure how much serotonin their brains were turning over. Turnover was lowest in winter. On any given day it tracked the hours of bright sunlight, and it rose rapidly as the light increased [5].

The clinical end of this was named in 1984, when a team of psychiatrists described 29 patients whose depressions arrived every autumn and lifted every spring, called the pattern seasonal affective disorder, and reported that in 11 of them, lengthening the day with bright artificial light had an antidepressant effect [6]. Twenty population studies since have put the prevalence of the full disorder anywhere between 0 and 9.7 per cent, with more of it at higher northern latitudes [7]. The diagnosed cases are only the visible part. When Finnish researchers interviewed 5,749 adults face to face, 85 per cent reported seasonal variations in mood and behaviour [8]. Sleeping longer, eating more and wanting less company in November is the majority experience of the north.

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A walk, a window, a lamp

The most reassuring fact about winter low mood is that its best-tested treatment is light itself. A meta-analysis in the American Journal of Psychiatry went through the published trials, kept only the 13 per cent that were rigorous enough, and found that bright light treatment for seasonal affective disorder had an effect size of 0.84, which the authors described as equivalent to the effects seen in most trials of antidepressant medication [9].

Canadian researchers then tested exactly that comparison. Over three winters, 96 patients with winter depression were given either a 10,000-lux light box for 30 minutes each morning plus a placebo capsule, or a dim placebo light plus fluoxetine. After 8 weeks, 67 per cent of each group had responded, and the light group had improved faster in the first week [10]. The protocol that came out of this research is simple: 10,000 lux, for 30 minutes, shortly after waking [11].

You do not have to own a lamp to use the principle. In one trial, patients with seasonal depression took a one-hour walk outdoors every morning for a week, while a comparison group sat in front of a weak artificial light. After that single week, 50 per cent of the walkers were in remission, against 25 per cent of the comparison group, and the walk had pulled their melatonin rhythm earlier [12]. Remember the winter campers: even December daylight is a signal of a different order from anything screwed into a ceiling.

And where you sit matters for the hours you cannot be outside. In a pilot study of 49 day-shift office workers, those with windows in their workplace received 173 per cent more white light during working hours, measured on the wrist, and slept on average 46 minutes longer each night than those without [13]. A desk turned towards the window is the cheapest light therapy there is.

The vitamin the sky stops making

Sunlight does a second job that has nothing to do with the eyes. Ultraviolet B rays striking the skin make vitamin D, but only when the sun stands high enough for those rays to get through the atmosphere. In 1988 researchers exposed samples of human skin to sunlight on cloudless days through the year. In Boston, at 42°N, the skin made no previtamin D3 at all from November through February. In Edmonton, at 52°N, the dead period ran from October through March [14]. Riga lies at 57°N and Tallinn at 59°N, further north than either city in the study. However bright a February noon looks on the snow, it is not making vitamin D.

The result shows up in blood. Across 55,844 Europeans, 13.0 per cent had vitamin D levels below 30 nmol/L averaged over the year, but that figure was 17.7 per cent among those sampled between October and March and 8.3 per cent in the summer half. By the wider definition of deficiency, below 50 nmol/L, the share was 40.4 per cent [15]. The Nordic Nutrition Recommendations 2023 set the intake for adults at 10 µg a day, and at 20 µg from the age of 75 and for anyone with little or no sun exposure [16], which from October to March describes most of us.

Vitamin D is the item on this list that comes from the fishmonger and the pharmacy: oily fish, eggs, fortified foods and, for most people at this latitude, a supplement through the dark half of the year. It is also why we wrote in August that late August decides how you feel in January. What the body stored in the bright months is what it is spending now.

Colour is stored light

Winter takes a second thing from the north besides light, and that is colour. The plants spent the bright months doing what we cannot, turning sunlight into chemistry and keeping it. A berry's pigment is a summer of light in a form that lasts until spring. We have written before about why nature paints its medicine in bright colours; the dark season is when it matters most, because it is when the plate turns beige.

Does eating colour change how people feel? It has been tested directly. In New Zealand, 171 young adults who ate little fruit and few vegetables were randomised for 14 days to carry on as usual, to receive reminders and vouchers, or simply to be handed two extra servings of fresh fruit and vegetables a day. The group given the produce improved in vitality, flourishing and motivation [17]. And when economists followed the food diaries of 12,385 Australian adults, people who increased their fruit and vegetable intake became happier and more satisfied with life within 24 months. For an increase of 8 portions a day, the gain in life satisfaction was comparable to moving from unemployment into work [18].

The darkest pigments have the most specific evidence. Anthocyanins are the purple-black pigments of aronia, haskap, blueberry and blackcurrant. A single wild blueberry drink carrying 253 mg of anthocyanins raised positive mood two hours later in 21 young adults and in 50 children, while a placebo drink did not [19]. Given every day for 4 weeks to 64 adolescents, the same amount left them with significantly fewer symptoms of depression than those on placebo [20]. And a 2025 meta-analysis that pooled 59 randomised controlled trials of anthocyanins and anthocyanin-rich foods found improvements in global cognition, visuospatial attention, episodic memory and working memory [21].

The north grows some of the richest sources of these pigments anywhere. Aronia carries 1,480 mg of anthocyanins per 100 g of fresh berry, the highest value of any food in the United States Department of Agriculture's survey [22]. When 101 healthy adults aged 40 to 60 took aronia extract every day for 24 weeks in a double-blind trial, their psychomotor speed, the quickness with which the hand follows the eye and the intention, improved significantly against placebo at the 90 mg dose [23]. Haskap, the blue honeysuckle that ripens before the strawberries, carries 79 to 93 per cent of its anthocyanins as a single compound, cyanidin-3-O-glucoside, at 68 to 649 mg per 100 g [24]. In a double-blind crossover study, 20 adults aged 62 to 81 recalled significantly more words 1.5 hours after haskap doses containing 200 and 400 mg of anthocyanins [25]. We press both berries on their own: Moon Berry is aronia and nothing else, and Blue North is pure haskap.

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The orange end of the spectrum

If anthocyanins are the dark end of the stored spectrum, vitamin C is the bright one, and it is one of the nutrients most closely tied to the plain feeling of having energy. The reason lies in the biochemistry. Vitamin C is a working part of the enzymes that make noradrenaline, the brain's signal for alertness, and carnitine, the molecule that carries fat into the furnaces of the cell to be burned. When the supply runs low, tiredness is one of the first things a person notices.

The trials bear this out. In a 6-week trial in 35 young men, those eating two kiwifruit a day who had started with the most mood disturbance saw it fall by 38 per cent, with fatigue down 38 per cent and vigour up 31 per cent, as the vitamin C in their blood rose [26]. A placebo-controlled trial in 167 adults whose vitamin C was low found that two kiwifruit a day brought blood levels to saturation within two weeks, and that well-being improved significantly in the same two weeks, with fatigue and mood disturbance easing alongside it [27]. And in a double-blind trial in young adults with inadequate vitamin C, 4 weeks of supplementation improved attention and absorption in work against placebo and shortened reaction times on a test of concentration [28].

Kiwifruit do not grow on the Baltic coast. Sea buckthorn does. Berries from European coasts carry 120 to 315 mg of vitamin C per 100 g [29], and pressed sea buckthorn juice around 173 mg per 100 ml [30]. Acerola, the tropical cherry, measures between 1,190 and 2,187 mg per 100 g of fresh fruit [31], an order of magnitude above citrus. These are the two fruits we press for the bright end of the spectrum: Sunthorn is pure sea buckthorn, and Red Ray is pure acerola. A small glass beside breakfast puts orange on the table at the hour the sky is still black.

Let the evening be dark

The other half of the light deficit is too much light at the wrong end of the day. In a study of 116 healthy volunteers, ordinary room light of under 200 lux in the hours before bed, compared with dim light, delayed the onset of melatonin in 99.0 per cent of people and shortened the body's melatonin night by about 90 minutes [32]. The modern winter day has it backwards: dim mornings and bright evenings, where the body is built for the opposite.

The old Latvian calendar knew this without measuring it. In many places the weeks between Miķeļi and Mārtiņi were veļu laiks, the time of the shades, when the ancestors were welcomed back to the house [33]. Mārtiņi, on 10 November, closed the autumn and opened the winter, with the field work done and the year turned indoors [34]. An evening lit by a stove and a candle gives the clock exactly the message it is waiting for. If your nights are restless all the same, our article on sleep and the second brain picks up where this one stops.

What to do this week

None of this needs equipment or a new routine built from nothing. It needs six small changes, in roughly this order of importance.

• Morning light first. Get outdoors as soon as the sky is light. The trial walk lasted an hour; half an hour on the way to work is a real start.
• Sit by the window. Move the desk, or at least breakfast and the lunch break, to where the day can reach you.
• Use a lamp if mornings are impossible. The protocol from the trials is a 10,000-lux light box for 30 minutes, soon after waking.
• Take vitamin D from October to March. The Nordic recommendation for adults is 10 µg a day; your doctor can measure your level with a simple blood test.
• Put colour on the table every day. A small glass of a dark berry juice, 100 ml to begin with, or something orange beside breakfast.
• Dim the evening. Lamps low after supper, screens down, and candles count.

As for which bottle, the four below are each a single plant, organic, cold-pressed, with nothing added. Choose by colour and by taste, and keep the one you will open every morning where you can see it.

One line of caution: a light box is not for everyone, so if you have bipolar disorder, an eye condition such as retinopathy, glaucoma or cataract, or take a medicine that makes you sensitive to light, speak to your doctor first [11], and low mood that lasts for weeks or closes down your days is a reason to see a doctor rather than a reason to buy a lamp.

The Baltic light deficit, in short

At 57°N the midwinter day lasts under seven hours and the sun sets before four. The body clock, set by light reaching the eye, drifts late; mood and energy follow. What helps is well tested: morning daylight or a 10,000-lux lamp, a desk by the window, vitamin D from October to March, colourful berries and fruit daily, and dim evenings.

Back to the window

At four o'clock tomorrow the window will turn into a mirror again, and it will go on doing so into January. Nothing in this article moves Riga any further south. But the face in the glass can belong to someone who walked to work in the grey light, who sits where the day can find them, who has orange and purple on the table, and who is about to turn the lamps down rather than up.

The dark season is long here, and people have lived well through it for a very long time. On the twenty-first of December the sun turns. From the next morning, every day is a little longer than the one before.

Frequently asked questions

How short is the shortest day in the Baltics?

In Riga the shortest day, 21 December, lasts 6 hours and 43 minutes, with sunrise at 09:00 and sunset at 15:43. Vilnius gets 7 hours and 14 minutes, Tallinn 6 hours and 3 minutes, and Helsinki 5 hours and 49 minutes. In Riga the sun sets before 16:00 every day from 22 November to 6 January.

Do light therapy lamps really work?

Yes. A meta-analysis of rigorous trials found bright light treatment for seasonal affective disorder had an effect size of 0.84, comparable to antidepressant medication [9], and in a head-to-head trial of 96 patients, 67 per cent responded to a 10,000-lux lamp used for 30 minutes each morning, the same share as responded to fluoxetine [10].

Can you make vitamin D from winter sun in Latvia, Estonia or Lithuania?

No. Skin exposed to cloudless winter sunlight made no previtamin D3 from November through February at 42°N, and from October through March at 52°N [14]. The Baltic capitals lie between 54°N and 59°N, so through the dark half of the year vitamin D has to come from food and supplements. The Nordic recommendation for adults is 10 µg a day [16].

Which foods and drinks help in the dark season?

Colourful ones. Young adults given two extra servings of fruit and vegetables a day improved in vitality and motivation within 14 days [17]. Wild blueberry has lifted mood, and aronia and other anthocyanin-rich berries have improved measures of cognition, in controlled trials [19][21][23], and vitamin C-rich fruit has reduced fatigue and improved well-being within two weeks in adults whose levels were low [27]. Oily fish and eggs supply vitamin D.

References

1. Berson DM, Dunn FA, Takao M. Phototransduction by retinal ganglion cells that set the circadian clock. Science. 2002;295(5557):1070–1073. doi:10.1126/science.1067262
2. Blume C, Garbazza C, Spitschan M. Effects of light on human circadian rhythms, sleep and mood. Somnologie. 2019;23:147–156. doi:10.1007/s11818-019-00215-x
3. Wright KP Jr, McHill AW, Birks BR, Griffin BR, Rusterholz T, Chinoy ED. Entrainment of the human circadian clock to the natural light-dark cycle. Current Biology. 2013;23(16):1554–1558. doi:10.1016/j.cub.2013.06.039
4. Stothard ER, McHill AW, Depner CM, Birks BR, Moehlman TM, Ritchie HK, et al. Circadian entrainment to the natural light-dark cycle across seasons and the weekend. Current Biology. 2017;27(4):508–513. doi:10.1016/j.cub.2016.12.041
5. Lambert GW, Reid C, Kaye DM, Jennings GL, Esler MD. Effect of sunlight and season on serotonin turnover in the brain. The Lancet. 2002;360(9348):1840–1842. doi:10.1016/S0140-6736(02)11737-5
6. Rosenthal NE, Sack DA, Gillin JC, Lewy AJ, Goodwin FK, Davenport Y, et al. Seasonal affective disorder: a description of the syndrome and preliminary findings with light therapy. Archives of General Psychiatry. 1984;41(1):72–80. doi:10.1001/archpsyc.1984.01790120076010
7. Magnusson A. An overview of epidemiological studies on seasonal affective disorder. Acta Psychiatrica Scandinavica. 2000;101(3):176–184. doi:10.1034/j.1600-0447.2000.101003176.x
8. Grimaldi S, Partonen T, Haukka J, Aromaa A, Lönnqvist J. Seasonal vegetative and affective symptoms in the Finnish general population: testing the dual vulnerability and latitude effect hypotheses. Nordic Journal of Psychiatry. 2009;63:397–404. doi:10.1080/08039480902878729
9. Golden RN, Gaynes BN, Ekstrom RD, Hamer RM, Jacobsen FM, Suppes T, et al. The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence. American Journal of Psychiatry. 2005;162(4):656–662. doi:10.1176/appi.ajp.162.4.656
10. Lam RW, Levitt AJ, Levitan RD, Enns MW, Morehouse R, Michalak EE, et al. The Can-SAD study: a randomized controlled trial of the effectiveness of light therapy and fluoxetine in patients with winter seasonal affective disorder. American Journal of Psychiatry. 2006;163(5):805–812. doi:10.1176/ajp.2006.163.5.805
11. Terman M, Terman JS. Light therapy for seasonal and nonseasonal depression: efficacy, protocol, safety, and side effects. CNS Spectrums. 2005;10(8):647–663. doi:10.1017/S1092852900019611
12. Wirz-Justice A, Graw P, Kräuchi K, Sarrafzadeh A, English J, Arendt J, et al. 'Natural' light treatment of seasonal affective disorder. Journal of Affective Disorders. 1996;37:109–120. doi:10.1016/0165-0327(95)00081-X
13. Boubekri M, Cheung IN, Reid KJ, Wang C-H, Zee PC. Impact of windows and daylight exposure on overall health and sleep quality of office workers: a case-control pilot study. Journal of Clinical Sleep Medicine. 2014;10(6):603–611. doi:10.5664/jcsm.3780
14. Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. Journal of Clinical Endocrinology & Metabolism. 1988;67(2):373–378. doi:10.1210/jcem-67-2-373
15. Cashman KD, Dowling KG, Škrabáková Z, Gonzalez-Gross M, Valtueña J, De Henauw S, et al. Vitamin D deficiency in Europe: pandemic? American Journal of Clinical Nutrition. 2016;103(4):1033–1044. doi:10.3945/ajcn.115.120873
16. Blomhoff R, Andersen R, Arnesen EK, Christensen JJ, Eneroth H, Erkkola M, et al. Nordic Nutrition Recommendations 2023. Copenhagen: Nordic Council of Ministers; 2023. doi:10.6027/nord2023-003
17. Conner TS, Brookie KL, Carr AC, Mainvil LA, Vissers MCM. Let them eat fruit! The effect of fruit and vegetable consumption on psychological well-being in young adults: a randomized controlled trial. PLoS One. 2017;12(2):e0171206. doi:10.1371/journal.pone.0171206
18. Mujcic R, Oswald AJ. Evolution of well-being and happiness after increases in consumption of fruit and vegetables. American Journal of Public Health. 2016;106(8):1504–1510. doi:10.2105/AJPH.2016.303260
19. Khalid S, Barfoot KL, May G, Lamport DJ, Reynolds SA, Williams CM. Effects of acute blueberry flavonoids on mood in children and young adults. Nutrients. 2017;9(2):158. doi:10.3390/nu9020158
20. Fisk J, Khalid S, Reynolds SA, Williams CM. Effect of 4 weeks daily wild blueberry supplementation on symptoms of depression in adolescents. British Journal of Nutrition. 2020;124(2):181–188. doi:10.1017/S0007114520000926
21. Micek A, Godos J, Giampieri F, et al. The effect of anthocyanins and anthocyanin-rich foods on cognitive function: a meta-analysis of randomized controlled trials. GeroScience. 2025. doi:10.1007/s11357-025-02008-7
22. Wu X, Beecher GR, Holden JM, Haytowitz DB, Gebhardt SE, Prior RL. Concentrations of anthocyanins in common foods in the United States and estimation of normal consumption. Journal of Agricultural and Food Chemistry. 2006;54(11):4069–4075. doi:10.1021/jf060300l
23. Ahles S, Stevens YR, Joris PJ, Vauzour D, Adam J, de Groot E, et al. The effect of long-term Aronia melanocarpa extract supplementation on cognitive performance, mood, and vascular function: a randomized controlled trial in healthy, middle-aged individuals. Nutrients. 2020;12(8):2475. doi:10.3390/nu12082475
24. Rupasinghe HPV, Arumuggam N, Amararathna M, De Silva ABKH. The potential health benefits of haskap (Lonicera caerulea L.): role of cyanidin-3-O-glucoside. Journal of Functional Foods. 2018;44:24–39. doi:10.1016/j.jff.2018.02.023
25. Bell L, Williams CM. A pilot dose–response study of the acute effects of haskap berry extract (Lonicera caerulea L.) on cognition, mood, and blood pressure in older adults. European Journal of Nutrition. 2019;58:3325–3334. doi:10.1007/s00394-018-1877-9
26. Carr AC, Bozonet SM, Pullar JM, Vissers MCM. Mood improvement in young adult males following supplementation with gold kiwifruit, a high-vitamin C food. Journal of Nutritional Science. 2013;2:e24. doi:10.1017/jns.2013.12
27. Conner TS, Fletcher BD, Haszard JJ, Pullar JM, Spencer E, Mainvil LA, et al. KiwiC for Vitality: results of a placebo-controlled trial testing the effects of kiwifruit or vitamin C tablets on vitality in adults with low vitamin C levels. Nutrients. 2020;12(9):2898. doi:10.3390/nu12092898
28. Sim M, Hong S, Jung S, Kim JS, Goo YT, Chun WY, et al. Vitamin C supplementation promotes mental vitality in healthy young adults: results from a cross-sectional analysis and a randomized, double-blind, placebo-controlled trial. European Journal of Nutrition. 2022;61(1):447–459. doi:10.1007/s00394-021-02656-3
29. Koskovac M, Cupara S, Kipic M, Barjaktarevic A, Milovanovic O, Kojicic K, Markovic M. Sea buckthorn oil — a valuable source for cosmeceuticals. Cosmetics. 2017;4(4):40. doi:10.3390/cosmetics4040040
30. Guo X, Zhuo L, Feng Y, Lin M, Le TN, Zhao M, Cai H. Bioactive components and functional applications of sea buckthorn: a review. Food Science & Nutrition. 2026;14(8). doi:10.1002/fsn3.72289
31. Moraes FP de, Costa RC, Morais CLM de, Medeiros FGM de, Fernandes TRN, Hoskin RT, Lima KMG de. Estimation of ascorbic acid in intact acerola (Malpighia emarginata DC) fruit by NIRS and chemometric analysis. Horticulturae. 2019;5(1):12. doi:10.3390/horticulturae5010012
32. Gooley JJ, Chamberlain K, Smith KA, Khalsa SBS, Rajaratnam SMW, Van Reen E, et al. Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. Journal of Clinical Endocrinology & Metabolism. 2011;96(3):E463–E472. doi:10.1210/jc.2010-2098
33. Latvian Ethnographic Open-Air Museum. Press release on the museum's evening of the shades (Veļu vakars), published on LV portāls, 24 October 2012. lvportals.lv/dienaskartiba/251756-tupenu-godi-un-velu-vakars-brivdabas-muzeja-2012
34. Latvian Ethnographic Open-Air Museum. Press release on the museum's Mārtiņi celebration, published on LV portāls, 7 November 2012. lvportals.lv/dienaskartiba/252016-martindienas-svinibas-brivdabas-muzeja-2012

This article is for educational purposes and is not medical advice. If you have a diagnosed condition, are pregnant or take regular medication, speak with your doctor or pharmacist before changing what you eat or drink.