Explainer

Vitamin D: how much do you really need?

The NHS advises that adults consider a daily supplement of 10 micrograms (400 IU) of vitamin D, especially in autumn and winter when sunlight is too weak to make enough through the skin, and some people are advised to take it all year. 10 micrograms equals 400 IU. The NHS also advises not taking more than 100 micrograms a day unless a clinician recommends it. This is information, not medical advice.

The NHS daily amount

The clearest figure to anchor to is the NHS advice that adults consider a daily supplement containing 10 micrograms of vitamin D. This is one of the few supplement recommendations the NHS makes for the general population, which is why it is worth knowing precisely. It applies to most adults, with some groups advised to take it throughout the year rather than only in the colder months.

Micrograms and IU

Vitamin D is labelled in micrograms (mcg) and international units (IU), and the conversion trips a lot of people up. 10 micrograms equals 400 IU. So a routine daily amount is 10 mcg or 400 IU, while a product labelled 1000 IU contains 25 micrograms, which is more than the routine NHS figure. Checking the conversion lets you compare products on a like-for-like basis.

Autumn and winter, and who needs more

From roughly October to March, UK sunlight is too weak for the skin to make vitamin D, which is why the NHS focuses its supplement advice on autumn and winter. Some groups, including people who are rarely outdoors and those who keep most of their skin covered, are advised to supplement all year. The EFSA-authorised roles for vitamin D include contributing to the maintenance of normal bones and muscle function and to the normal function of the immune system; these are general nutritional roles, not treatments.

The safe upper limit

More is not better. The NHS warns that taking too much vitamin D over a long period can be harmful, and advises adults not to take more than 100 micrograms a day unless a clinician recommends it. Stick to label guidance, avoid doubling up across a multivitamin and a separate vitamin D, and speak to your GP or pharmacist before taking high-strength products, especially in pregnancy.

Read more

For forms, sources and named UK brands, see our guide to vitamin D and the best vitamin D supplement UK roundup. Vitamin D matters at every stage, from pregnancy and postnatal through to the senior years. Verified figures are gathered on our UK women's health statistics page.

Frequently asked questions

This is information, not medical advice, and is not a substitute for a registered clinician. Always read product labels and speak to your GP or pharmacist before starting a supplement. Source: NHS, Vitamin D (nhs.uk).