Quick answer

What is vitamin d deficiency?

Vitamin D deficiency means low levels of the vitamin that helps bones, muscles and immune function. In the UK, many people are low — especially in winter — because sunlight is the main source. Symptoms include tiredness, bone pain and muscle weakness. Supplements are recommended for most UK adults in autumn and winter.

Why vitamin D matters in the UK

Vitamin D helps the body absorb calcium and phosphate — essential for healthy bones, teeth and muscles. It also plays a role in immune function. In the UK, sunlight between April and September is the main source — the body makes vitamin D in skin exposed to UVB rays. From October to March, the sun is too weak for most people to make enough, which is why deficiency is common.

Symptoms of deficiency

Many people with low vitamin D feel no symptoms. When symptoms occur, they may include:

  • tiredness and general aches
  • bone pain — especially lower back, pelvis, hips and legs
  • muscle weakness — difficulty climbing stairs or getting up from a chair
  • mood changes — low mood (research links deficiency to depression, though cause is unclear)
  • frequent infections

Severe deficiency causes rickets in children (soft, bowing bones) and osteomalacia in adults (bone pain and weakness from softened bones). These are uncommon in the UK today but still occur.

Who is at higher risk

  • people with darker skin — more melanin reduces vitamin D production
  • people who cover most of their skin outdoors for cultural or religious reasons
  • those who are housebound or in care homes
  • people with malabsorption — coeliac disease, Crohn’s disease, after bariatric surgery
  • obesity — vitamin D is stored in fat and less available
  • older adults — skin produces vitamin D less efficiently

NHS supplementation advice

Current UK guidance:

  • All adults should consider 10 micrograms (400 IU) daily from October to March
  • At-risk groups should take supplements year-round
  • Breastfed babies need vitamin D drops from birth (formula is fortified)
  • Children aged 1–4 need 10 micrograms daily year-round

Supplements are widely available from pharmacies and supermarkets. Vitamin D3 (cholecalciferol) is generally preferred over D2.

Diagnosis and treatment

A GP may test vitamin D levels if you have symptoms and risk factors. Blood tests measure 25-hydroxyvitamin D:

  • Deficient — usually below 25 nmol/L — treated with higher prescribed doses for 6–8 weeks, then maintenance
  • Insufficient — 25–50 nmol/L — maintenance supplementation
  • Sufficient — above 50 nmol/L

You do not need a blood test before starting a standard preventive supplement.

Food sources

Diet provides limited vitamin D:

  • oily fish — salmon, sardines, mackerel
  • egg yolks
  • fortified foods — some cereals, margarine, milk alternatives

Sunlight and supplements remain more important than diet alone in the UK climate.

Safe supplementation

Stick to recommended doses. Do not take very high doses without medical supervision — excess vitamin D causes hypercalcaemia (high calcium), which can damage kidneys and bones. The NHS maintenance dose of 10 micrograms daily is safe for long-term use.

Vitamin D and other conditions

Low vitamin D is associated with tiredness and may contribute to muscle and bone pain mistaken for other conditions. Correcting deficiency sometimes improves symptoms, though tiredness has many causes — see our tiredness guide if symptoms persist after treatment.

Deficiency is also linked to osteoporosis risk in older adults alongside calcium intake and exercise.

Getting sensible sun exposure

In summer, brief sun exposure on forearms and lower legs without sunscreen — about 10–15 minutes for lighter skin, longer for darker skin — helps maintain levels. Avoid burning. Balance sun exposure with skin cancer risk — supplements cover winter gaps safely.

Common questions

What are the symptoms of vitamin D deficiency?
Many people have no obvious symptoms. When present, they include tiredness and general aches, bone pain especially in the lower back, pelvis and legs, muscle weakness, mood changes, and frequent infections. Severe deficiency causes rickets in children and osteomalacia (soft bones) in adults.
Who should take vitamin D supplements in the UK?
The NHS recommends all adults consider 10 micrograms (400 IU) daily from October to March. Year-round supplementation is advised for people who get little sun exposure, have dark skin, cover their skin outdoors, or are in care homes.
Can I get enough vitamin D from food?
Only a small amount comes from diet — oily fish, egg yolks, fortified cereals and spreads. Sunlight remains the main source for most people, which is why UK guidance emphasises supplements in winter.
How is vitamin D deficiency treated?
A GP confirms deficiency with a blood test and prescribes higher-dose supplements for a period, then maintenance doses. Over-the-counter supplements prevent deficiency in most people without needing a blood test first.
Can you take too much vitamin D?
Yes. Very high doses over long periods can cause calcium build-up and harm kidneys and bones. Stick to recommended doses — 10 micrograms daily for maintenance, or as prescribed by a GP for treatment.

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