Vitamin D

Vitamin D's main job is to keep calcium and phosphorus in balance in the body so that bones and teeth can be built and maintained. Without enough vitamin D the body cannot absorb the calcium it needs, and the result over time is soft, weakened bones: rickets in children, osteomalacia in adults, and a higher risk of falls and fractures in older people.

What makes vitamin D unusual among nutrients is that the body can make it. When bare skin is exposed to UVB radiation from sunlight, a precursor in the skin is converted into vitamin D and then activated by the liver and kidneys. In the UK summer (roughly April to September) most people make enough this way from short daily exposure to bare arms and face. In autumn and winter the sun is too low in the sky for the relevant UVB to reach the ground, and the body cannot make vitamin D no matter how long you stand outside. That is why the UK position became, in 2016, a daily supplement recommendation for everyone.

People with darker skin produce vitamin D less efficiently from a given amount of sun. People who cover most of their skin for cultural or religious reasons get little or none. Children under 5, pregnant and breastfeeding women, adults 65 and over, and anyone with limited time outdoors are advised to take a 10ug supplement year-round, not only in autumn and winter.

Vitamin D in food is genuinely scarce. The table below is honest about that: even the best food sources, eaten in normal UK portions, struggle to deliver the 10ug daily target. This is the structural reason the NHS recommends a supplement rather than telling people to eat more of a single food.

Values per 100g come from USDA SR Legacy and McCance and Widdowson 7th edition; the site's food entries currently store macros only.

The bottom line on food: a single portion of oily fish gets you to roughly a day's vitamin D, and eating it twice a week (the NHS Eatwell guidance) helps. But for the rest of the week, especially from October to March, the 10ug supplement is the practical answer the NHS now recommends.

Mushrooms exposed to UV: some UK retailers sell mushrooms labelled as a vitamin D source because they have been UV-treated. Untreated mushrooms contain very little. Check the pack.

The current UK position on vitamin D comes from SACN's 2016 review. It replaced earlier age-banded UK RNIs with a single recommendation that applies to almost everyone, and an explicit note for the youngest babies.

NHS Healthy Start vitamins: qualifying pregnant women, breastfeeding mums, and children under 4 in the Healthy Start scheme receive free vitamin drops (containing vitamins A, C, and D for children; vitamin D for adults).

Low vitamin D is common in the UK, and the symptoms can be vague. Many people with low vitamin D feel nothing at all until levels are very low or until a related problem (a fracture, persistent muscle pain, a child's bone growth issue) brings it to a doctor's attention.

Adult symptoms

• Tiredness, low mood
• Muscle weakness, especially around the hips and shoulders
• Bone pain, often in the lower back, hips, pelvis, or ribs
• Muscle aches
• Higher risk of falls in older adults
• In severe long-running cases: osteomalacia (softened bones) and a higher risk of fractures

Children's symptoms

• Delayed walking, soft or bowed legs (rickets in severe cases)
• Slow growth
• Bone pain or tenderness
• Muscle weakness
• Dental problems

Who is at higher risk in the UK

• Everyone, from October to early March. Latitude alone gets us there; the sun is too low for skin synthesis.
• People with darker skin. More melanin means more sun is needed to make the same amount of vitamin D.
• People who cover most of their skin in public for cultural or religious reasons.
• Adults 65 and over. Skin synthesis falls with age, and many older adults spend less time outdoors.
• Pregnant and breastfeeding women. Needs are higher and the consequences for the baby's bone development are real.
• Babies and young children. Especially breast-fed babies (breast milk is low in vitamin D).
• People with limited time outdoors: shift workers, people who are housebound, people who use sunscreen routinely (which is sensible for skin-cancer prevention, but blocks vitamin D synthesis).
• People with malabsorption conditions: coeliac disease, Crohn's disease, cystic fibrosis, after bariatric surgery.

When to see your GP: persistent bone pain, muscle weakness, repeated falls, a child with delayed walking or bowed legs, or any of the above symptoms in a risk group. A simple blood test for serum 25-hydroxyvitamin D gives the answer. Treatment of confirmed deficiency uses higher doses than the everyday 10ug for a short period, then drops back to the maintenance dose.

Vitamin D from sunlight is self-regulating: the body shuts the conversion down at a point and cannot overdose from sun. Food is too low in vitamin D to cause harm in any normal pattern. The risk is from supplements.

NHS upper-limit guidance: do not take more than 100 micrograms of vitamin D a day. (Pregnant and breastfeeding women included.)

Too much vitamin D over time causes the body to absorb too much calcium, which can build up in the blood. Symptoms of excess include:

• Loss of appetite
• Nausea, vomiting
• Thirst and frequent urination
• Constipation
• Stomach pain
• Confusion
• In long-running excess: kidney damage and softening of arteries

The supplements sold over the counter in the UK in mainstream supermarkets and pharmacies are almost always at 10ug or 25ug a day, well below the limit. The problem arises with very high-dose imports, and with people stacking multiple supplements that each contain vitamin D without noticing.

Babies under 1 year: the safe range is 8.5 to 10ug. Do not give a baby an adult-dose supplement.

This is the entry where the NHS supplement position is unusually clear, because food cannot reliably cover it in a UK climate.

The standard NHS recommendation:

• Everyone aged 4 and over: consider a daily supplement of 10ug of vitamin D, particularly in autumn and winter.
• Children aged 1 to 3: 10ug every day, all year.
• Babies under 1 year: 8.5 to 10ug a day from a baby-specific vitamin D supplement. Babies on 500ml or more of infant formula a day do not need it (formula is already fortified).
• Pregnant and breastfeeding women: 10ug a day, all year.
• People with darker skin, those who cover most of their skin outdoors, and those who spend little time outdoors: 10ug a day, all year.
• Adults aged 65 and over: 10ug a day, all year.

NHS Healthy Start vitamins: qualifying pregnant and breastfeeding women, and qualifying children under 4, can get free vitamin drops through the scheme.

Choosing a supplement: a 10ug tablet costs very little and lasts months. Look for "10 micrograms" (which may also be written as "400 IU", the older international units; both mean the same thing). Avoid very-high-dose products unless prescribed for confirmed deficiency.

If a GP diagnoses deficiency: a short course at higher dose (commonly 50,000 IU once a week for several weeks, or a calculated daily dose) is used to restore levels, then a 10ug daily maintenance dose continues afterwards. Follow-up blood tests track the response.

• The other vitamin-and-mineral entry most relevant here: Magnesium (involved in activating vitamin D in the body).
• Best food sources: oily fish such as Salmon and Mackerel; small amounts in eggs.
• Vitamin D is a fat-soluble vitamin: the Eatwell Guide covers the role of fats in absorbing it.

• NHS. Vitamins and minerals: Vitamin D. nhs.uk/conditions/vitamins-and-minerals/vitamin-d. Adult and child intake, supplement guidance.
• SACN. Vitamin D and Health. 2016. The review that established the UK 10ug position for the general population.
• SACN. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. Department of Health Report 41 (1991).
• NHS. How to get vitamin D from sunlight.
• NHS. Healthy Start scheme.
• Public Health England. McCance and Widdowson's The Composition of Foods, 7th summary edition (2015).

This page is reference information for UK shoppers. It is not medical advice.