What the evidence says about vitamin D and other supplements for anxiety

Walk down any pharmacy aisle and you will find a shelf of small bottles promising calm. Vitamin D, fish oil, magnesium, herbal blends. Some of them have real research behind them for something. The question here is narrower: what is actually established about any of them for anxiety, and what is not?

The short version

• The NHS advises a daily vitamin D supplement in autumn and winter for most people, but a recent pooled analysis of trials found no significant effect on anxiety symptoms.
• Omega-3 fish oil and magnesium have some encouraging results, but the reviewers call for better-designed trials, and the magnesium review rates its evidence as poor quality.
• Supplements can interact with other medicines, and more is not better. Check with a pharmacist or your GP before adding one.
• A supplement does not replace the things that the NHS lists for anxiety: talking therapies, self-help and, where needed, medicine.

Vitamin D: sensible advice, separate question

The NHS says adults need 10 micrograms of vitamin D a day. Between October and early March, we do not make enough from sunlight, so everyone should consider a daily supplement then. People at higher risk of low levels are advised to take one all year, including those who are rarely outdoors. The page also warns against taking more than 100 micrograms a day, because too much over a long period can cause calcium to build up and harm the bones, kidneys and heart.

That is general advice for the population. It is a different question from whether vitamin D eases anxiety.

A 2024 systematic review pooled randomised trials of vitamin D3 and was mainly about depression (31 trials, 24,189 people). For depressive symptoms it found a small short-term benefit that faded in longer trials. For anxiety, seven trials were available, with 332 people given vitamin D and 309 controls. Vitamin D3 had no significant effect on anxiety symptoms, and the authors called for more high-quality trials.

Two honest readings sit side by side. Seven trials is not a lot, so this is not proof that vitamin D could never help anyone. But it does mean that nobody can currently tell you it works for anxiety. If a product says otherwise, the claim is running ahead of the evidence.

Omega-3: an encouraging but uncertain signal

A 2018 review and meta-analysis looked at omega-3 polyunsaturated fatty acids. It drew on 19 studies. Omega-3 use was associated with lower anxiety symptoms compared with controls, with an effect size (Hedges' g) of 0.374. The 95 per cent confidence interval ran from 0.081 to 0.666, which is a wide range: from barely different from nothing to fairly large.

There are further details in the abstract worth knowing. The benefit was greater in people with a clinical diagnosis than in those without one, and it was significant only at doses of at least 2,000 milligrams a day. The authors concluded that omega-3 may help reduce symptoms of clinical anxiety, and asked for better-designed studies. That is an encouraging result with an honest label on it: possible, imprecise, and not yet settled.

Magnesium: suggestive, but poor quality

A 2017 systematic review in the journal Nutrients looked at magnesium, alone or combined with up to five other ingredients, and included 18 studies. All of them were in people already vulnerable to anxiety, such as those with mild anxiety, premenstrual syndrome or high blood pressure. Several reported benefits, and the authors wrote that existing evidence is suggestive of a beneficial effect. They also said the quality of that evidence is poor and that well-designed randomised controlled trials are needed. Magnesium had no effect in the postpartum group.

In some of the included studies magnesium was combined with other ingredients, so even a good result may not tell you which ingredient did what.

Herbal remedies need extra care

St John's wort is a herbal medicine traditionally used for mild low mood and anxiety. The Medicines and Healthcare products Regulatory Agency (MHRA) has warned that it can reduce the effectiveness of hormonal contraceptives, and advises women using hormonal contraception not to take St John's wort products. By December 2014 its Yellow Card scheme had received 19 reports of suspected interactions since 2000, including 15 unplanned pregnancies. The MHRA also notes that some unlicensed products carry no interaction warning, which does not mean they do not interact.

The wider point is that "natural" does not mean "has no effects". If you take any prescribed medicine, tell your pharmacist before you add a supplement.

What to do with this

First, if you want to take vitamin D in the autumn and winter because the NHS suggests it, that is reasonable. Just do not expect it to settle anxiety. And if what you actually suspect is a deficiency behind how you feel, that is a question for a blood test rather than the supplement aisle: the physical conditions that get mistaken for anxiety covers what a GP checks first.

Second, if you are tempted by omega-3 or magnesium, treat them as an experiment, not a treatment. Check the dose and the label, ask a pharmacist about interactions, and do not stop or swap a prescribed medicine to make room for one.

Third, look at what the NHS puts on its page for treating generalised anxiety disorder. It says a GP will usually advise talking therapies before prescribing medicine, and it lists self-help such as books, online tools or courses, calming breathing, yoga or pilates, regular exercise, a healthy diet and enough sleep. Supplements do not appear there. You can also refer yourself directly to an NHS talking therapies service if you are 18 or over.

If what draws you to a supplement is wanting a small, regular step you can take, therapy can be small too: brightloaf's sessions are built around 20 minutes.

A supplement can be a reasonable thing to try. It should not be the only thing you try.

Anxiety that is getting in the way of work, sleep or relationships is worth raising with a GP, whatever you are taking. This post is general information and is not a substitute for personal medical advice.