Skip to content
Winnowleaf home

Vitamin D for Winter Blues and Seasonal Depression: What the Trials Show

Vitamin D is unlikely to lift winter low mood unless you are short of it. In 18,353 older adults, 2,000 IU a day for about five years did not prevent depression (grade A), and the few small trials in seasonal depression disagree (grade C). Bright light therapy has the strongest evidence for seasonal affective disorder (grade B). UK advice is a small daily dose in autumn and winter; adults shouldn't exceed 4,000 IU daily without medical advice.

Published How we grade evidenceEditorial policy

The short version

  • Vitamin D did not prevent depression: 2,000 IU a day for about five years in 18,353 adults over 50 made no difference. Grade A (Okereke 2020).
  • It may ease symptoms a little in people already depressed, mostly in short trials. Grade B (Ghaemi 2024).
  • For seasonal affective disorder itself, the vitamin D trials are tiny and disagree. Grade C (Gloth 1999; Frandsen 2014).
  • Bright light therapy has the strongest evidence for seasonal depression. Grade B (Pjrek 2020).
  • Big yearly doses backfired: 500,000 IU once a year led to more falls and fractures in older women. Grade B (Sanders 2010).

Seasonal affective disorder (SAD) is depression that returns in autumn or winter and lifts in spring. It affects about 1.5% to 9% of people, more the farther they live from the equator (Nussbaumer-Streit 2019). Milder "winter blues" are more common. Because your skin makes vitamin D from sunlight, and in the UK the sun is too weak to do so from October to early March (NHS), vitamin D is the supplement most people reach for. Here is what the trials show.

Does vitamin D help seasonal depression?

Grade C. Only a handful of small trials have tested it, and they point in different directions. In 15 people with SAD, a single dose of 100,000 IU of vitamin D improved depression scores after a month, while the light-therapy comparison group did not change (Gloth 1999). In 34 hospital workers with winter mood symptoms, 70 micrograms (2,800 IU) a day for 3 months did no better than placebo (Frandsen 2014). A systematic review of diet and SAD concluded that no nutrition approach, vitamin D included, has been shown to help (Yang 2020). Upper limit for adults: 4,000 IU a day; take more only with blood tests or your clinician's advice (NHS).

Does vitamin D help the winter blues?

Grade B for no clear benefit in people without depression. In a 5-day trial of 44 healthy people in late winter, 400 or 800 IU raised self-rated positive mood (Lansdowne 1998). Longer and larger trials found nothing. In 1,621 women over 70 in the UK, calcium with 800 IU of vitamin D a day did not change mental well-being over 6 months (Dumville 2006). A yearly 500,000 IU dose each autumn or winter for 3 to 5 years did not change any measure of mental health, even though blood levels rose 41% (Sanders 2011).

Does vitamin D prevent or treat depression?

Grade A that it does not prevent depression. The largest trial, VITAL-DEP, gave 18,353 adults aged 50 and over 2,000 IU of vitamin D3 a day or placebo for a median of 5.3 years. New and returning depression was no less common on vitamin D (12.9 vs 13.3 cases per 1,000 people a year), and mood scores did not differ (Okereke 2020).

Grade B for a small effect in people who already have symptoms, and the meta-analyses are mixed. A 2014 analysis of 7 trials found no overall effect, but a moderate one in the 2 trials of people with clinical depression (Shaffer 2014). A 2024 analysis of 31 trials (24,189 adults) found a small drop in depressive symptoms, larger in people with depression, and only in trials of up to 6 months; trials longer than a year showed no effect (Ghaemi 2024). Vitamin D is not a substitute for depression treatment.

What works best for seasonal depression?

Grade B for bright light therapy, the strongest evidence of any self-help option. Light therapy means sitting near a bright light box, usually in the morning. Pooling 18 trials (610 patients), it lowered depression scores more than dim light or a sham device, and people were about 40% more likely to respond; the trials were small and of mixed quality (Pjrek 2020). A 2024 network meta-analysis of 21 trials (1,037 people) ranked light therapy above the other treatments compared, again on low-quality evidence (Chen 2024).

In a trial of 177 adults with SAD, 6 weeks of 10,000-lux light for about 30 minutes each morning worked about as well as a 6-week course of group CBT, a talking therapy; just under half of each group went into remission (Rohan 2015). Whether starting light before symptoms appear stops SAD from returning is unknown: Cochrane found only one small trial (Nussbaumer-Streit 2019). Prescription treatments also exist; a doctor can talk through them with you.

Should you take vitamin D in winter?

For bones and general health, many people should, but at ordinary doses. UK health advice is that adults consider 10 micrograms (400 IU) a day in autumn and winter (NHS). The Endocrine Society's 2024 guideline suggests against taking more than the recommended daily intake to prevent disease if you are a healthy adult under 75, and against routine vitamin D blood tests; it does suggest supplements for people 75 and over, in pregnancy and for high-risk prediabetes (Demay 2024). It also favours a daily dose over big occasional doses for people over 50 (Demay 2024). For colds and flu, see our cold and flu season guide. For children and in pregnancy, ask a clinician about the amount.

Do other supplements help winter low mood?

  • Fish oil (omega-3): in the same large trial, 1 g a day for about five years did not prevent depression; depression was slightly more common on fish oil (13.9 vs 12.3 cases per 1,000 people a year), in one large trial. Grade B (Okereke 2021).
  • St John's wort: may help mild to moderate depression, but it interacts dangerously with many medicines, including antidepressants and birth control pills (NCCIH). Don't use it without asking your doctor or pharmacist.
  • Saffron, lavender and others: see our supplements for anxiety guide for what the trials show on mood.

What we'd skip

  • Big yearly or "loading" doses of vitamin D. 500,000 IU once a year raised falls and fractures in older women (Sanders 2010) and did nothing for mood (Sanders 2011).
  • Vitamin D above the upper limit to fix your mood. It didn't prevent depression at 2,000 IU a day for five years (Okereke 2020), and the Endocrine Society advises against going above the recommended intake if you are healthy and under 75 (Demay 2024).
  • A vitamin D test just to check, if you have no risk factors. The Endocrine Society found no trial evidence for routine testing (Demay 2024).
  • Fish oil to keep winter depression away. No prevention in 18,353 adults (Okereke 2021).

Safety and interactions

  • Too much vitamin D raises blood calcium, which can weaken bones and damage the kidneys and heart; adults should not take more than 4,000 IU (100 micrograms) a day without medical advice (NHS; NIH ODS). Add up every source, including multivitamins, with our upper-limit calculator.
  • Big single doses: a yearly 500,000 IU dose raised falls, most of all in the 3 months after each dose, and fractures (Sanders 2010).
  • Medicines and kidney disease: if you take prescription medicines or have kidney disease, ask your pharmacist or doctor before taking more than a standard daily dose. Our vitamin D page lists its graded uses.
  • St John's wort weakens many medicines (NCCIH); see St John's wort with SSRIs and with birth control.
  • Light boxes: ask your doctor which light and schedule suit you, especially if you have an eye condition or have had episodes of mania.

When to see a doctor

  • Right now: if you have thoughts of harming yourself, call or text 988 in the US (the 988 Suicide & Crisis Lifeline) or your local emergency number.
  • Soon: low mood, loss of interest, oversleeping or overeating that lasts more than two weeks or comes back every winter. These can be seasonal depression, which is treatable.
  • Before starting: high-dose vitamin D, light therapy or St John's wort if you take prescription medicines, have kidney disease, or have had episodes of mania.

Don't stop or change a prescribed medicine on your own; ask the prescriber or pharmacist. If you are pregnant or breastfeeding, ask your doctor or midwife how much vitamin D to take.

FAQ

Does vitamin D help seasonal depression? The trials are few, tiny and disagree (grade C). Bright light therapy has much better evidence for seasonal depression (grade B).

Should I take vitamin D in winter? Many adults are advised to consider 10 micrograms (400 IU) a day in autumn and winter for general health. A 2,000 IU daily dose didn't prevent depression in a large trial; one pooled analysis found bigger short-term drops in symptoms at higher doses, mostly in people with depression. Upper limit for adults: 4,000 IU a day; take more only with blood tests or your clinician's advice.

Does vitamin D prevent depression? No. In a trial of 18,353 adults, 2,000 IU a day for about five years did not lower the risk of depression (grade A).

What is the best treatment for seasonal affective disorder? Bright light therapy and talking therapy (CBT) worked about equally well in a trial of 177 adults. Prescription treatments are also available from a doctor.

Is it safe to take a big dose of vitamin D once a year? We'd avoid it. A yearly dose of 500,000 IU led to more falls and fractures in older women.

Sources

  1. Okereke OI, 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. JAMA. 2020. PubMed 32749491 · doi:10.1001/jama.2020.10224
  2. Ghaemi S, et al. The effect of vitamin D supplementation on depression: a systematic review and dose-response meta-analysis of randomized controlled trials. Psychol Med. 2024. PubMed 39552387 · doi:10.1017/S0033291724001697
  3. Gloth FM 3rd, et al. Vitamin D vs broad spectrum phototherapy in the treatment of seasonal affective disorder. J Nutr Health Aging. 1999. PubMed 10888476
  4. Frandsen TB, et al. Vitamin D supplementation for treatment of seasonal affective symptoms in healthcare professionals: a double-blind randomised placebo-controlled trial. BMC Res Notes. 2014. PubMed 25125215 · doi:10.1186/1756-0500-7-528
  5. Pjrek E, et al. The Efficacy of Light Therapy in the Treatment of Seasonal Affective Disorder: A Meta-Analysis of Randomized Controlled Trials. Psychother Psychosom. 2020. PubMed 31574513 · doi:10.1159/000502891
  6. Sanders KM, et al. Annual high-dose oral vitamin D and falls and fractures in older women: a randomized controlled trial. JAMA. 2010. PubMed 20460620 · doi:10.1001/jama.2010.594
  7. Nussbaumer-Streit B, et al. Light therapy for preventing seasonal affective disorder. Cochrane Database Syst Rev. 2019. PubMed 30883670 · doi:10.1002/14651858.CD011269.pub3
  8. Yang Y, et al. The Role of Diet, Eating Behavior, and Nutrition Intervention in Seasonal Affective Disorder: A Systematic Review. Front Psychol. 2020. PubMed 32903693 · doi:10.3389/fpsyg.2020.01451
  9. Lansdowne AT, et al. Vitamin D3 enhances mood in healthy subjects during winter. Psychopharmacology (Berl). 1998. PubMed 9539254 · doi:10.1007/s002130050517
  10. Dumville JC, et al. Can vitamin D supplementation prevent winter-time blues? A randomised trial among older women. J Nutr Health Aging. 2006. PubMed 16554952
  11. Sanders KM, et al. Annual high-dose vitamin D3 and mental well-being: randomised controlled trial. Br J Psychiatry. 2011. PubMed 21525520 · doi:10.1192/bjp.bp.110.087544
  12. Shaffer JA, et al. Vitamin D supplementation for depressive symptoms: a systematic review and meta-analysis of randomized controlled trials. Psychosom Med. 2014. PubMed 24632894 · doi:10.1097/PSY.0000000000000044
  13. Chen ZW, et al. Treatment measures for seasonal affective disorder: A network meta-analysis. J Affect Disord. 2024. PubMed 38220102 · doi:10.1016/j.jad.2024.01.028
  14. Rohan KJ, et al. Randomized Trial of Cognitive-Behavioral Therapy Versus Light Therapy for Seasonal Affective Disorder: Acute Outcomes. Am J Psychiatry. 2015. PubMed 25859764 · doi:10.1176/appi.ajp.2015.14101293
  15. Demay MB, et al. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2024. PubMed 38828931 · doi:10.1210/clinem/dgae290
  16. Okereke OI, et al. Effect of Long-term Supplementation With Marine Omega-3 Fatty Acids vs Placebo on Risk of Depression or Clinically Relevant Depressive Symptoms and on Change in Mood Scores: A Randomized Clinical Trial. JAMA. 2021. PubMed 34932079 · doi:10.1001/jama.2021.21187