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Supplements: how do you know what you actually need?

By Kerri Hopkins · 4 min read · 20 October 2026

The shelves are full of tubs promising energy, glowing skin, calm and “hormone balance”. So how do you know what you need?

Start with food

The NHS says most people should get all the nutrients they need from a varied, balanced diet. That means at least five portions of fruit and veg a day, wholegrain starchy foods, beans, pulses, fish, eggs or meat, dairy or fortified alternatives, and plenty of fluids. Some people do need extra, though.

Who may need what

• Vitamin D. Everyone should consider 10 micrograms a day in autumn and winter, when sunlight is not enough. Do not take more than 100 micrograms (4,000 IU) a day.
• Folic acid. If you are trying for a baby or pregnant, 400 micrograms a day, from before you conceive until 12 weeks pregnant. Some women need a higher dose from a GP.
• In pregnancy. Do not take cod liver oil or supplements containing vitamin A (retinol), as too much can harm your baby.
• Vitamin B12. Vegans may not get enough, because it is not naturally found in plant foods. Ask about a supplement.
• Iron. Do not take it just in case. The right amount and type depend on your blood tests, so speak to your GP. Read my guide to iron, ferritin and fatigue.

More is not better

Some supplements can cause harm at high doses. For example, the NHS says not to take more than 25mg of zinc a day unless advised by a doctor, and that 400mg or less of magnesium from supplements is unlikely to cause harm. Supplements can also interact with medicines.

Five questions before you buy

1. What is it for, and do I have a reason to think I am low?
2. Could I get this from food?
3. Does it contain more than the safe upper limit?
4. Does it interact with anything I take?
5. Have I asked a pharmacist or GP?

A pharmacist is free to talk to, and knows more than a social media post.

When a test helps

If you suspect a deficiency, such as tiredness, hair loss or cramps, ask your GP about a blood test before you start spending. It can save you money, and it can pick up things a supplement will not fix.

Sources

NHS: Vitamins and minerals · NHS: Other vitamins and minerals · NHS: Vitamin D · NHS: Vitamin B12 · NHS: Vitamins and supplements in pregnancy · NHS: A balanced diet

BioHer provides educational information only. It is not medical advice, diagnosis or treatment, and it does not replace your GP or other healthcare professional. If symptoms feel urgent or severe, call 111 for urgent advice, or 999 in an emergency.