What vitamins should I take? A 2-minute check based on NHS advice

How the vitamin quiz works

The check asks up to 9 questions: sex, age, pregnancy, diet, fish, sunlight, symptoms, medicines and goals. Some questions only appear when they matter. For example, we ask about pregnancy only if you’re a woman aged 18–50, and about fish only if you’re not vegan.

Each answer is checked against a set of rules taken from official public-health advice, not from supplement marketing. At the end you get a list in four parts, with links to our full guides.

Which official advice the rules follow

• NHS: vitamin D, vegan diets, fish in your diet and iron.
• NICE NG247 (the 2025 guideline on nutrition in pregnancy): folic acid and vitamin D before and during pregnancy.
• NIH ODS (the US Office of Dietary Supplements): who runs low on B12, which medicines reduce its absorption, and who might need a multivitamin.

We lead with the NHS and NICE because they’re the advice your GP and pharmacist follow. Where UK guidance is silent, we use the NIH ODS fact sheets, which give clear figures and are updated regularly. To see when the sun is strong enough where you live, try our vitamin D sunlight calendar.

Which vitamins do I need? Official advice in one table

NICE recommends the higher 5 mg folic acid dose for people with diabetes, sickle cell disease, thalassaemia or a personal or family history of neural tube defects. It also applies if you take medicines that affect folate, such as some epilepsy and HIV medicines. A BMI of 25 or more isn’t, on its own, a reason for the higher dose.

How to read your result

Your result comes in four groups:

• “The basics”: what official advice says for people in your situation, such as vitamin D3 in winter or B12 for vegans.
• “Test first, then supplement”: things you shouldn’t take blind. Iron is the usual one, so ask about ferritin and a full blood count first.
• “For your goals”: what’s been studied for sleep, energy, skin and other goals, and what supplements won’t do.
• “Worth knowing”: warnings about medicines, pregnancy, gut conditions and iron. Don’t skip this part.

A short list is good news: your diet is probably doing the work. No need to pad it out to ten bottles.

Why it doesn’t suggest doses beyond public-health advice

The quiz suggests maintenance doses for healthy adults. Treatment doses are for your GP to set after a test, and for good reason:

• The NHS warns that more than 100 micrograms (4,000 IU) of vitamin D a day could be harmful.
• Iron above 20 mg can cause constipation, nausea and stomach pain, and an overdose can be fatal for children.
• Retinol (vitamin A) in pregnancy can harm your baby.
• Low B12 caused by a gut condition is sometimes treated with injections, not tablets.

So where a test matters, you’ll see “get a blood test” rather than “take 5,000 IU”.

When to see your GP instead

• Tiredness or weakness lasting more than a few weeks.
• Pins and needles or memory problems, which can be signs of low B12.
• Heavy periods or signs of anaemia, such as breathlessness or pale skin.
• Pregnancy, or kidney, liver or gut disease.
• Trying for a baby while taking regular medicines or living with diabetes: you may need 5 mg of folic acid, and some medicines are best switched before you conceive.
• Regular medicines, especially warfarin, levothyroxine or metformin. Check our vitamin compatibility chart.
• Choosing for a child.

How to choose on iHerb after the quiz

1. Start with “The basics” and open the guide for each item.
2. Choose the dose official advice recommends, not the biggest one on the shelf.
3. Add up the doses across all your bottles, including any multivitamin, and compare them with our supplements A–Z.
4. Leave anything in “Test first” until you have results.
5. Compare products by cost per day.

Before you order, run through the short list below. It takes a minute and catches the usual slip-ups: a double dose from two bottles, or iron taken “just in case”.

Prefer to browse by ingredient instead? Open our supplements catalogue.