Vitamin D and Bone Health: How Much Do You Actually Need?

What does vitamin D actually do for your bones?

Vitamin D's core job is to help your body absorb calcium and mineralise bone. The NHS explains that vitamin D helps regulate the amount of calcium and phosphate in the body — nutrients needed to keep bones, teeth and muscles healthy. NHS, 2023 The Royal Osteoporosis Society puts it more plainly: vitamin D's main job is to help the body absorb calcium from the gut and to stop it being lost through the kidneys. Royal Osteoporosis Society, 2021

The biology behind that is well established. Vitamin D is a secosteroid hormone that is essential for calcium absorption and bone mineralization, and it is positively associated with bone mineral density. Nutrients, 2010

When levels stay too low for too long, bone cannot mineralise properly. Prolonged, severe vitamin D deficiency causes rickets in children and osteomalacia in adults. Nutrients, 2010 Osteomalacia results from impaired mineralisation of bone, and its main features are diffuse bone pain and tenderness, muscle weakness and fragility fractures. JBMR Plus, 2020 This is why vitamin D matters alongside the other building blocks of bone — something we cover in more depth in our guide to calcium, protein and vitamin D for bone health.

How much vitamin D do you need for bone health in the UK?

In the UK, everyone aged 1 and over needs 10 micrograms (400 IU) of vitamin D a day. That is the NHS recommendation for children over the age of 1 and adults. NHS, 2023 Public Health England and NICE give the same headline figure, advising that 10 micrograms of vitamin D are needed daily for healthy bones and muscles. Public Health England / NICE, 2020

The Royal Osteoporosis Society echoes this for the general population, suggesting everyone aim for 10 micrograms (400 IU) a day alongside sensible sun exposure. Royal Osteoporosis Society, 2021 So the everyday number to remember is simple: 10 micrograms, which is the same as 400 international units.

Do you really need to take vitamin D in autumn and winter?

For most people in the UK, yes. Between October and early March, the sun in the UK is too low in the sky for your skin to make vitamin D, so the NHS advises that everyone should consider taking a daily supplement containing 10 micrograms of vitamin D during autumn and winter. NHS, 2023

In spring and summer, most people can make enough from short periods of sunlight on the skin plus a balanced diet, so a supplement is less likely to be needed for the general population during those months. NHS, 2023 The autumn-to-spring window is the practical reason so many people in the UK top up over winter.

Who should take a vitamin D supplement all year round?

Some groups should not rely on sunlight at all and are advised to supplement year-round. The NHS lists people who are not often outdoors — for example, if they are frail or housebound — those living in a care home, people who usually cover most of their skin when outdoors, and people with an African, African-Caribbean or south Asian background as groups who should take a supplement throughout the year. NHS, 2023

Older adults are a particular focus for bone health. The International Osteoporosis Foundation recommends that adults aged 60 and over take a supplement at a dose of 800 to 1,000 IU a day to help reduce the risk of falls and fractures. International Osteoporosis Foundation, 2024 Vitamin D is only one part of a wider picture, though — movement, diet and strength all matter, as we explain in how to improve bone density naturally.

How much vitamin D is right if you have osteoporosis or are older?

If you have osteoporosis or a confirmed deficiency, a higher dose than the everyday 10 micrograms is often advised — but on clinical guidance, not guesswork. The Royal Osteoporosis Society notes that people with osteoporosis, especially those taking osteoporosis medication, may be prescribed 20 micrograms (800 IU) a day. Royal Osteoporosis Society, 2021

UK clinical guidance points the same way. The National Osteoporosis Guideline Group advises that patients should be prescribed vitamin D supplements of at least 800 IU a day if they have identified vitamin D insufficiency or risk factors for insufficiency, and adds that in the context of osteoporosis a level of 800 up to 2,000 IU daily may be appropriate. National Osteoporosis Guideline Group (NOGG), 2024 NOGG also flags that housebound people and those in residential or nursing care are more likely to need calcium and vitamin D supplementation. National Osteoporosis Guideline Group (NOGG), 2024

These higher doses are conditional — they apply where insufficiency or specific risk factors have been identified, which is why the wording is "may be prescribed" rather than a blanket recommendation. If osteoporosis is on your radar, your GP is the right person to set your dose.

Where do you get vitamin D — sunlight and food?

Most of your vitamin D comes from summer sunlight on your skin, topped up by a few foods. From about late March to the end of September, sunlight on bare skin is the main source for most people. NHS, 2023

Dietary sources are more limited, which is part of why a winter supplement is recommended. The NHS lists oily fish — such as salmon, sardines and mackerel — red meat, egg yolks, and fortified foods such as some fat spreads and breakfast cereals. NHS, 2023 If you are building a bone-friendly plate more broadly, our guide to the best foods for bone health sets vitamin D alongside calcium and protein.

Can you take too much vitamin D?

Yes — more is not better, and very high doses can do harm. The NHS is clear that taking too many vitamin D supplements over a long period can cause problems, and advises adults not to take more than 100 micrograms (4,000 IU) a day, adding that 10 micrograms is enough for most people. NHS, 2023

Clinical guidance also warns against big occasional "boluses". NOGG advises that routine intermittent large doses — for example, 60,000 IU or more at once — are not recommended, because they have been linked to a reported increased risk of falls and fractures. National Osteoporosis Guideline Group (NOGG), 2024

Do you need a blood test before taking vitamin D?

Usually not. The Royal Osteoporosis Society notes that you do not need a blood test before taking a vitamin D supplement, unless it is being done as part of a broader bone health assessment. Royal Osteoporosis Society, 2021 For most people, taking the recommended 10 micrograms a day is straightforward and does not need testing first.

Where vitamin D does fit is inside a fuller look at your bone health. Supplements support bone, but they do not replace clinical care or tell you what is happening inside your skeleton. A radiation-free REMS scan can establish a baseline and help monitor your bone health over time, sitting alongside a GP-guided approach to diet and supplements — which is exactly what our bone health assessment is designed to do.

---

This article is part of our bone health series. For the wider picture, see our guide to calcium, protein and vitamin D for bone health.