Seasonal affective disorder (SAD) is a form of depression that follows a recurring seasonal pattern, most often beginning in autumn or winter and improving in spring. Symptoms can include persistent low mood, loss of interest, hopelessness, irritability, poor concentration, increased appetite, sleeping more than usual and marked tiredness. A minority experience a summer pattern instead.
Reduced daylight is thought to affect circadian rhythm and brain signalling involving melatonin and serotonin. SAD is not simply vitamin D deficiency, although low vitamin D can coexist. Diagnosis generally requires depression at the same time of year for at least two years and an assessment for other causes of low mood.
Treatment and daily structure
Recognising serious symptoms
See a GP if a seasonal change in mood is affecting daily life or established treatment is not helping. Antidepressants and talking therapies such as cognitive behavioural therapy are established options. Thoughts of self-harm or suicide require urgent mental-health support.
Light therapy helps some people, although evidence is not conclusive and it is not usually provided by the NHS. A light box should be UV-free, carry a UKCA or CE mark and typically provide 10,000 lux. Seek medical advice first if you have an eye condition, take a light-sensitising medicine or have bipolar disorder, because bright light can occasionally trigger hypomania or mania.
Natural daylight, regular exercise, consistent sleep and wake times, social contact and continuing usual activities can make winter more manageable. A varied diet with regular meals supports general brain and metabolic health; excluding gluten, dairy or caffeine is unnecessary unless a personal problem has been identified.
Useful supplements
Supplements should be selected for the individual rather than used automatically. Product directions and advice from an appropriately qualified professional should take precedence over general information.
| Supplement | Effects |
|---|---|
| Vitamin D3 | Supports normal bone, muscle and immune function and may correct low status during months with limited sunlight. |
| Krill oil or marine fish oil | Provides EPA and DHA that support normal brain and cell-membrane function and inflammatory regulation. |
| Magnesium citrate | Supports normal nervous-system function and pathways involved in serotonin production and relaxation. |
| Zinc citrate | Supports normal brain enzymes, immune function and antioxidant protection. |
| Vitamin B complex | Provides vitamins required for energy metabolism and normal nervous-system function. |
| Phosphatidylserine or lecithin | Supplies phospholipids and choline-related compounds that support cell membranes and normal brain function. |
| Vitamin C | Provides antioxidant support and contributes to normal psychological and immune function. |
| Broad-spectrum beneficial bacteria | Intended to support intestinal microbial balance and digestive health. |
| Evening primrose oil | Provides GLA, a fatty acid used to make cell-signalling compounds. |
The source doses of vitamin D, zinc and vitamin C are too high for routine unsupervised use. Excess vitamin D can cause dangerous calcium levels; long-term high-dose zinc can produce copper deficiency; vitamin C may cause diarrhoea and increase kidney-stone risk in susceptible people. Supplements do not replace treatment for depression.
A practical plan begins before symptoms usually intensify and combines daylight exposure, structured activity, sleep regularity and evidence-based care. Tracking mood across the year can show whether the pattern and the response to treatment are genuinely seasonal.
Looking for personalised nutrition and lifestyle support? An FNTP member may be able to help you explore an approach suited to your individual needs. Find an FNTP practitioner.
This article is for general education and does not replace individual medical advice, diagnosis or treatment.
