Vitamin D: sunlight, food, and the NHS supplement advice

Vitamin D helps your body absorb calcium, which keeps bones, teeth and muscles healthy, and it plays a role in the immune system. Your body makes most of it from sunlight on your skin, which is why UK health bodies advise considering a small daily supplement over the darker months. This guide covers how to get enough and what the evidence does and doesn't support.

This is general information, not personalised medical advice. If you think you may be deficient or you take regular medicines, speak to a doctor or pharmacist.

What does vitamin D do?

Vitamin D helps regulate the amount of calcium and phosphate in the body, which is needed to keep bones, teeth and muscles healthy. A lack of it can lead to rickets in children and to bone pain and softening (osteomalacia) in adults. Vitamin D also supports normal immune function.

Vitamin D is involved in many other processes, and you will see it linked to claims about everything from mood to infection risk. Its role in bone health is the best established; broader claims are less certain and the evidence is still developing.

How do we get vitamin D?

From about late March to the end of September, most people in the UK can make enough vitamin D from sunlight on their skin. From October to early March, the sun in the UK is not strong enough, so it has to come from food or supplements.

Food sources are limited but include:

• Oily fish such as salmon, mackerel and herring
• Egg yolks
• Red meat and liver
• Fortified foods such as some breakfast cereals and fat spreads

Because few foods contain much vitamin D, it is hard to get enough from diet alone in winter — which is the reason behind the supplement advice below.

What does the NHS advise about supplements?

UK advice is that everyone should consider taking a daily supplement containing 10 micrograms (400 IU) of vitamin D during autumn and winter. Some people should take it all year round, including those who:

• Have little or no sun exposure — for example people in care homes or who usually cover their skin outdoors
• Have darker skin (for example African, African-Caribbean or south Asian backgrounds), as it can be harder to make enough from sunlight

Babies and young children have their own recommendations. If you are unsure what applies to you, a pharmacist can help.

D3 vs D2 — does it matter?

Vitamin D comes in two main forms: D3 (cholecalciferol), usually from animal sources or lichen, and D2 (ergocalciferol), from plant sources. Both raise vitamin D levels, and many UK supplements use D3. People following a vegan diet can look for D3 derived from lichen, or use D2. The practical advice for most people is simply to take a supplement that provides 10 micrograms a day, rather than to worry about the form.

What about D3 with K2?

Combined vitamin D3 and K2 supplements are popular, based on the idea that vitamin K2 helps direct calcium to bones rather than arteries. This is a plausible area of research, but the evidence that adding K2 produces meaningful health benefits for most people is still developing and not settled. For the average person following UK advice, a straightforward 10 microgram vitamin D supplement is what the guidance recommends. If you take a blood-thinning medicine such as warfarin, do not start a vitamin K supplement without medical advice, as vitamin K can interfere with it.

Do vertical ridges on my nails mean a vitamin deficiency?

Usually not. Vertical ridges that run from the base to the tip of the nail are very common and tend to become more noticeable with age. On their own they are generally a normal change, not a reliable sign of vitamin deficiency. It is a popular online claim, but it does not hold up as a diagnostic test.

That said, you should tell a doctor about new nail changes — especially horizontal ridges, pitting, spoon-shaped nails, or changes in colour — as these can sometimes point to a health issue worth checking. The way to confirm a deficiency is a conversation with a clinician and, if appropriate, a blood test, not a look at your nails.

How much is too much, and when should I test?

For most adults, a 10 microgram daily supplement is enough. Do not take more than 100 micrograms (4,000 IU) a day, as too much vitamin D over time can cause calcium to build up and harm the bones, kidneys and heart. Children have lower limits.

You do not usually need a routine vitamin D blood test. Consider speaking to a doctor if you have symptoms such as bone or muscle pain, or if you are in a higher- risk group and want advice on testing or dosing. Supplements support a healthy diet and lifestyle — they are not a substitute for either, or for medical care.

For nutrients that work alongside a balanced diet, you may also find our guides to magnesium and omega-3 fish oil useful.