Vitamin D and the Winter Blues: Why It Still Matters

By Lindsay Powers | Nutritional Therapist & Health Writer, Naturally Healthy News

Published: November 2026 | Last reviewed: November 2026

Every winter, as the days shorten, the same advice appears: top up your vitamin D. Often it comes with a bigger promise attached, that the supplement will lift your mood through the dark months. The first part is well founded. The second is where the research gets more complicated.

This guide explains why so many people run short of vitamin D in winter and what it does for the body. It also covers what large trials say about mood and seasonal affective disorder, and how official advice differs between countries.

Why do so many people run short of vitamin D in winter?

Mainly because the sun does most of the work, and in winter it stops doing it well. Vitamin D is unusual among nutrients because most of it isn’t eaten. It’s made in the skin when ultraviolet B (UVB) rays from the sun strike it, then activated by the liver and kidneys. [1]

That system works well in summer and struggles in winter. The NHS says that from October to early March, sunlight in the UK isn’t strong enough for the body to make enough vitamin D. [2] In the southern states of Australia, where winter runs from June to August, health bodies say people can still keep their levels up with time outdoors in the middle of the day. Enough skin needs to be exposed, and it may take a few hours. [3] [4] UVB rays also don’t pass through glass, so time spent behind a window doesn’t produce vitamin D. [1]

Food rarely fills the gap. Oily fish, red meat, egg yolks and fortified foods such as some cereals and spreads contain vitamin D, but the NHS says it’s difficult to get enough from food alone. [2]

The shortfall is common. A study of 55,844 Europeans found that 13% had blood levels below 30 nmol/L, a common cut-off for deficiency. That’s about 12 ng/mL, the unit used in the US. About 4 in 10 fell below 50 nmol/L (20 ng/mL), a higher bar that some experts prefer. [5]

Deficiency was more common between October and March than in the summer months, and far more common in people with dark skin. The authors called the rates concerning and said they require action from a public health perspective.

Our guide to winter vitamin D deficiency covers the signs and who is most at risk.

What does vitamin D actually do?

Mainly, it keeps your bones, teeth and muscles healthy. Vitamin D helps regulate calcium and phosphate, the minerals those tissues depend on. Without enough, children can develop rickets, a condition that deforms the bones, and adults can develop osteomalacia, which causes bone pain. Together with calcium, vitamin D also helps protect older adults against osteoporosis. [2] [1]

Regulators have recognised these roles. The health claims authorised for vitamin D in Great Britain and the EU cover calcium absorption, bones, teeth, muscle function and the immune system. None of them concerns mood. [6]

Is low vitamin D linked to low mood?

Yes, in observational studies, though that doesn’t prove low vitamin D causes low mood. These studies track what people do and what happens to them without assigning a treatment. A 2013 meta-analysis pooled 14 studies covering 31,424 people. [7] Those with the lowest vitamin D levels developed depression at about twice the rate of those with the highest.

The authors were clear that this doesn’t show cause and effect, and they called for randomised trials. Low mood can reduce time outdoors, appetite and activity, which could in turn lower vitamin D. The link may run in either direction, or both may share a cause.

Does taking vitamin D protect your mood?

In the largest trials so far, no. Two of them put the question to a direct test, and between them they followed nearly 40,000 adults.

VITAL-DEP, a US trial, gave 18,353 adults aged 50 or over either 2,000IU (50 micrograms) of vitamin D3 daily or a placebo, and followed them for a median of 5.3 years. Depression occurred at almost the same rate in both groups, and average mood scores were virtually identical. [8] The authors concluded that the findings do not support using vitamin D3 to prevent depression in adults without depressive symptoms at the start.

D-Health, in Australia, randomised 21,315 adults aged 60 to 84 to a monthly high dose or a placebo and tracked depression for up to five years. It found no overall difference either. [9] There was a small improvement among people already taking antidepressants at the start, but the authors described this as subgroup evidence, and results like that can arise by chance. It’s a reason for further trials, not a reason to change treatment.

So what does this tell us? Vitamin D isn’t a mood shield for healthy older adults. That doesn’t make it pointless, because bones and muscles are the jobs it has always been best evidenced for. Both trials also ran in general populations of older adults, so they say little about younger adults or people with clearly low levels.

Could vitamin D help people who already have depression?

Possibly, as an add-on to standard treatment, but the evidence isn’t yet strong enough to say. A 2026 analysis pooled 15 trials in 962 people with depression or significant depressive symptoms and found a large improvement with vitamin D. [10] Its authors concluded that it may work as an add-on to standard treatment. The trials varied widely, though, so the average result should be read with caution.

A 2023 analysis of 41 trials and more than 53,000 adults found a smaller effect and rated the certainty of the evidence as very low, with concerning risk of bias in most studies. [11] A 2024 review of 31 trials found a benefit mainly in people with depressive symptoms, and no significant effect on anxiety. [12]

These reviews are likely to share many of the same trials, so they shouldn’t be counted as three independent confirmations. They may also differ from the big trials because they test something different. The large trials looked at preventing depression in people without it, while the reviews pool smaller trials in people who already have symptoms, using varied doses.

Researchers are now asking whether vitamin D could work alongside standard treatment. That’s a promising question, and it isn’t yet an answer.

What actually helps seasonal affective disorder?

For seasonal affective disorder (SAD), health services list light therapy, talking therapies and antidepressants, and vitamin D isn’t among them. SAD is a type of depression with a seasonal pattern, usually appearing in winter. The talking therapies listed include cognitive behavioural therapy (CBT). [13]

The US National Center for Complementary and Integrative Health reached a similar view. It says low blood levels of vitamin D are often found in people with SAD, but that vitamin D alone isn’t considered an effective treatment and the evidence is mixed. [14] Its digest summarises three small studies: two found no benefit, and one very small study of 15 people found improvement. It dates from 2019, so newer trials may have appeared since.

Light therapy uses a bright lamp, usually 10,000 lux, for a set time each morning. The NHS says it’s not usually available on the NHS because the evidence on how well it works is limited, though many people find it helps. It advises speaking to your doctor first and choosing a lamp designed for the purpose. A 2016 trial found that CBT designed for SAD outperformed light therapy two winters later, as summarised by the same digest.

What can you do this winter?

Sunshine alone isn’t always enough, as our piece on vitamin D3 in summer explains, including how sunscreen fits in. A few practical steps cover most people.

• Get outside in daylight around midday when you can, and protect your skin when the UV index is 3 or above. [3]
• Include foods that contain vitamin D, such as oily fish, egg yolks and fortified products, but don’t expect food alone to close the gap. [2]
• Keep moving, keep in touch with other people and keep to a routine, which are the everyday steps the NHS lists for SAD. [13]
• If you have dark skin, cover most of your skin outdoors, are housebound or rarely go outside, ask your doctor whether a blood test or supplement makes sense. [2] [4]
• If low mood follows a seasonal pattern, speak to your doctor about light therapy and talking therapies rather than relying on a supplement. [13]

How much vitamin D do you need?

Official advice differs by country, and the differences are worth knowing. The UK recommends a routine winter supplement. The US sets a daily intake target from all sources. Australia leans on sunlight, with supplements for people found to be low.

Country (source)	What it advises	Upper limit
UK (NHS) [2]	10 micrograms (400IU) daily in autumn and winter, and all year for people at higher risk, such as those with dark skin or who rarely go outdoors	100 micrograms (4,000IU)
US (National Institutes of Health) [1]	15 to 20 micrograms (600 to 800IU) daily from all sources, depending on age	100 micrograms (4,000IU)
Australia (NHMRC and healthdirect) [15] [3]	Adequate intake of 5 micrograms (200IU) for adults to 50, 10 micrograms (400IU) from 51 to 70, and 15 micrograms (600IU) over 70, mostly from sunlight. A supplement if your doctor finds you’re low	80 micrograms (3,200IU)

 

The Australian values date from 2005 and 2006, and Healthdirect says supplements aren’t generally recommended there unless a doctor finds you’re low.

Where you live, how much skin you expose, your skin tone and your diet all change what you need. Routine blood tests aren’t recommended for most healthy people in Australia, but a test can help if you’re at higher risk. [4] Levels of 50 nmol/L (20 ng/mL) or more are described as adequate or sufficient for most people. Tiredness and low mood have many causes, so symptoms alone can’t confirm a deficiency.

More isn’t better. Upper limits for adults sit between 80 and 100 micrograms (3,200 to 4,000IU) daily. Taking too much over a long period can raise calcium in the blood (hypercalcaemia), which can weaken bones and damage the kidneys and heart. Sunlight can’t cause an overdose.

Some trial doses were much higher. The 2026 analysis covered doses of 1,000 to 12,000IU daily, and its authors reported greater improvement around 5,000IU. [10] The 2024 review modelled its largest effect at 8,000IU, though with a very wide margin of error. [12] Several of these doses are above the upper limits. They were given within research studies and aren’t a basis for self-dosing.

Who should be careful with vitamin D supplements?

• If you take more than one supplement containing vitamin D, add up the total, because the upper limit applies to your whole intake.
• If you have a medical condition, ask your doctor first, because you may need less than the standard amount.
• If you use blood-thinning medicine such as warfarin, check with your prescriber before taking any product that also contains vitamin K. [16]
• If you’re pregnant or breastfeeding, follow your national guidance and your doctor’s advice, and stay below the upper limit.

Low mood that persists, or that affects daily life, is a reason to speak to your doctor whatever your vitamin D level. If you have thoughts of harming yourself, seek help straight away.

Frequently asked questions

Is vitamin D worth taking even if it doesn’t lift your mood?

Bone and muscle health are what vitamin D has most clearly been shown to support, so it matters whatever your mood. Whether you need a supplement depends on your sun exposure, skin tone, location and diet. In the UK the NHS advises one in autumn and winter, while elsewhere a doctor may suggest a blood test first. Any mood benefit would be a bonus, not the reason to take it.

Can you get enough vitamin D from food and sunlight alone?

Many people can in sunnier places or seasons. Australian guidance says most Australians meet their needs from sun exposure, while the NHS says UK sunlight isn’t strong enough from October to early March and that food alone rarely covers the gap. Oily fish and eggs contribute some vitamin D but shouldn’t be relied on for the full amount.

How long might vitamin D take to affect mood?

No timeframe is established. In the 2024 meta-analysis, benefits appeared in trials lasting up to about six months, then faded in longer trials, and trials lasting over a year showed none. [12] The largest, longest trials found no effect.

Can vitamin D replace antidepressants or therapy?

No. Where trials have found a benefit, vitamin D was tested as an add-on, and the evidence for that is still uncertain. Don’t stop prescribed medicine without speaking to your doctor or prescriber.

Final thoughts

Vitamin D is one of the best-known nutrients for winter, and the reasons hold up. The sun makes less of it when days are short, food rarely covers the gap, and low levels are common. Its best-established job is keeping bones, teeth and muscles healthy.

Mood is a separate question. Low levels are linked with depression, but the largest trials show that supplements don’t prevent it in older adults, and the evidence for people who already have depression is still uncertain. For seasonal affective disorder, light therapy, talking therapies and antidepressants are the treatments health services list.

So make sure you’re getting enough vitamin D for your bones and muscles, whether that’s from sunshine, food or a supplement that national guidance or your doctor suggests. Stay within the upper limit, and look to daylight, movement, support and your doctor for your mood.

References

1. National Institutes of Health, Office of Dietary Supplements. Vitamin D: fact sheet for health professionals. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
2. NHS. Vitamin D: how to get it, who needs it and how much is safe. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
3. healthdirect Australia. Vitamin D and your health. Last reviewed February 2026. https://www.healthdirect.gov.au/healthy-living/food-and-nutrition/vitamin-d-and-your-health
4. NPS MedicineWise (Australia). Vitamin D in winter. https://www.nps.org.au/news/vitamin-d-in-winter
5. Cashman KD, Dowling KG, Skrabakova Z, et al. Vitamin D deficiency in Europe: pandemic? Am J Clin Nutr. 2016;103(4):1033-1044. doi:10.3945/ajcn.115.120873. PMID: 26864360. https://doi.org/10.3945/ajcn.115.120873
6. Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods (vitamin D entries). Official Journal of the European Union, 2012. Retained in Great Britain legislation. https://www.legislation.gov.uk/eur/2012/432/annexes/adopted
7. Anglin RES, Samaan Z, Walter SD, McDonald SD. Vitamin D deficiency and depression in adults: systematic review and meta-analysis. Br J Psychiatry. 2013;202:100-107. doi:10.1192/bjp.bp.111.106666. PMID: 23377209. https://pubmed.ncbi.nlm.nih.gov/23377209/
8. Okereke OI, Reynolds CF 3rd, Mischoulon D, et al. Effect of long-term vitamin D3 supplementation vs placebo on risk of depression or clinically relevant depressive symptoms and on change in mood scores: a randomized clinical trial (VITAL-DEP). JAMA. 2020;324(5):471-480. doi:10.1001/jama.2020.10224. PMID: 32749491. https://doi.org/10.1001/jama.2020.10224
9. Rahman ST, Waterhouse M, Romero BD, et al. Effect of vitamin D supplementation on depression in older Australian adults (D-Health Trial). Int J Geriatr Psychiatry. 2023;38(1):e5847. doi:10.1002/gps.5847. PMID: 36462182. https://doi.org/10.1002/gps.5847
10. Liu HH, Liu TH, Liu CY, Wu JY, Lin CH, Lai CC. Efficacy of vitamin D supplementation in patients diagnosed with depression: a dose-response meta-analysis of randomized controlled trials. Front Nutr. 2026;13:1772451. doi:10.3389/fnut.2026.1772451. PMID: 41923913. https://doi.org/10.3389/fnut.2026.1772451
11. Mikola T, Marx W, Lane MM, et al. The effect of vitamin D supplementation on depressive symptoms in adults: a systematic review and meta-analysis of randomized controlled trials. Crit Rev Food Sci Nutr. 2023;63(33):11784-11801. doi:10.1080/10408398.2022.2096560. https://doi.org/10.1080/10408398.2022.2096560
12. Ghaemi S, Zeraattalab-Motlagh S, Jayedi A, Shab-Bidar S. The effect of vitamin D supplementation on depression: a systematic review and dose-response meta-analysis of randomized controlled trials. Psychol Med. 2024;54(15):3999-4008. doi:10.1017/S0033291724001697. https://doi.org/10.1017/S0033291724001697
13. NHS. Seasonal affective disorder (SAD): overview and treatment. https://www.nhs.uk/mental-health/conditions/seasonal-affective-disorder-sad/overview/
14. National Center for Complementary and Integrative Health (NCCIH). Seasonal affective disorder and complementary health approaches: what the science says. Clinical digest, January 2019. https://www.nccih.nih.gov/health/providers/digest/seasonal-affective-disorder-and-complementary-health-approaches-science
15. National Health and Medical Research Council (Australia and New Zealand). Nutrient Reference Values: vitamin D. Endorsed 2005; Commonwealth of Australia, 2006. https://www.eatforhealth.gov.au/sites/default/files/2022-04/n35-vitamind_0.pdf
16. NHS. Vitamin K: how to get it and what it does. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-k/

 

Disclaimer: The information in this article is intended for general informational purposes only and does not constitute medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your GP or a qualified healthcare provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you have read here.