Open Source Apothecary At Home / Mind and sleep

Winter low mood: light, and the things that are not a supplement

Bright light therapy has randomised evidence for seasonal affective disorder. It is the intervention, and it is not a supplement.

remedy

Seasonal affective disorder is a recurrent depressive pattern with a seasonal onset, usually in winter at high latitude. At 39.66 N the winter day is short and the light is weak, and the intervention with the best evidence is bright light.

Light therapy works. A randomised trial of bright light exposure in seasonal affective disorder showed substantial improvement in depression measures, and light therapy is first-line for the condition in the guidelines. It is not a wellness gadget claim; it is a treatment with an effect size comparable to antidepressants for this indication in the trials. The practical requirements matter: a high-intensity light box (around 10,000 lux) used for about 30 minutes each morning, at eye level, without looking directly into it, started in autumn before symptoms peak and continued through winter. Morning use is important — evening light shifts the circadian phase the wrong way and disrupts sleep.

Natural outdoor light helps less than a light box. An overcast winter day is far below 10,000 lux. A morning walk outdoors is good for other reasons and is not equivalent.

What else has evidence. Regular aerobic exercise; behavioural and cognitive therapy; and consistent sleep timing, which is a genuine lever in a seasonal pattern. Vitamin D adequacy where deficient — the observational association with depression is real and correcting a deficiency is reasonable, though trials of supplementation for depression have been largely negative.

St John's wort has trials in depression and interacts with a long list of drugs. Its photosensitivity is an obvious mismatch with a condition where light therapy is the treatment.

The red flags are the same as depression's. Seasonal affective disorder can be severe, and it can involve suicidal thoughts. A person with significant winter low mood needs clinical care — light therapy and therapy — not a supplement trial. And a depressive episode that is not seasonal is a different diagnosis needing a different plan.

What the studies found

Preparation

Light therapy — the treatment

• A light box of about 10,000 lux, positioned at eye level and slightly off to the side
• About 30 minutes each morning, soon after waking
• Do not stare into it. The eyes should be open and the light in the visual field while you read or eat.
• Start in early autumn, before the symptoms peak, and continue through winter
• Lower-intensity boxes need proportionally longer sessions; verify the lux rating rather than assuming
• Morning, not evening. Evening light shifts the circadian phase the wrong way and worsens sleep.

Timing and sleep

• Consistent wake time seven days a week
• Get outside in the morning, which reinforces the same phase signal
• Reduce evening screen light and bright light in the hours before bed

What else has evidence

• Regular aerobic exercise, 30-45 minutes most days
• CBT and behavioural activation, both with randomised evidence in depression
• Winter social contact, which is a real protective factor
• Vitamin D where deficient; it corrects a deficiency rather than treating the mood

St John's wort — with the cautions

• Trials in depression exist; it interacts with a very long list of drugs including hormonal contraception, immunosuppressants and anticoagulants
• It is photosensitising, which is a poor fit in a condition treated with bright light
• Do not combine it with an SSRI or other serotonergic drug

The supplements sold for winter mood

• Nothing here has evidence comparable to light therapy
• Do not spend on a winter-mood supplement instead of a light box and a clinician's assessment

The framing

• Seasonal patterns are treatable and the treatment is not exotic
• A low mood that is not seasonal is a different diagnosis; the treatment differs

Cautions and interactions

• Light therapy in the evening can shift the circadian phase and worsen sleep. Use it in the morning.
• Do not stare directly into a light box, and stop if it causes headache, eye irritation or agitation.
• Light therapy is contraindicated in some eye conditions and with some photosensitising drugs — including St John's wort. Ask.
• St John's wort interacts with many drugs and is photosensitising.
• Do not use a supplement instead of light therapy and clinical assessment.
• Bipolar disorder: light therapy and antidepressants can precipitate a switch to mania. This needs a clinician's involvement.

When this is not a self-care problem — get help

• Any suicidal thought or plan — get help now. In the US, call or text 988.
• A sudden switch to elevated, agitated or unusually energetic mood — urgent assessment; this can occur in bipolar disorder.
• Psychosis, severe agitation, or inability to care for yourself — emergency assessment.

Related

• Low mood and depression
• Insomnia: what works before the herbs
• Vitamin D: the supplement, the sun, and the U-curve
• Anxiety: kava, lavender and the herbs with trials

Sources

1. Hormonal Modulation with Withania somnifera: Systematic Review and Meta-Analysis of Randomized-controlled Trials. Planta medica 2026; doi:10.1055/a-2802-8363 PubMed 41740946
2. The Effects of Aerobic and Resistance Exercise on Depression and Anxiety: Systematic Review With Meta-Analysis. International journal of mental health nursing 2025; doi:10.1016/j.psychres.2019.112601 PubMed 40432290
3. Exercise Interventions for Depression, Anxiety, and Quality of Life in Older Adults With Cancer: A Systematic Review and Meta-Analysis. JAMA network open 2025; doi:10.1200/JCO.23.02780 PubMed 39903465
4. Impact of postpartum physical activity on maternal depression and anxiety: a systematic review and meta-analysis. British journal of sports medicine 2025; doi:10.1136/bjsports-2024-108478 PubMed 39500542
5. Effects of sleep hygiene education for insomnia: A systematic review and meta-analysis. Sleep medicine reviews 2025; doi:10.1016/j.smrv.2025.102109 PubMed 40449065