In short: Vitamin D keeps bones, teeth and muscles healthy. In the UK, sunlight is too weak to make enough vitamin D from about October to early March, so the NHS advises everyone to consider a daily 10 microgram (400 IU) supplement in autumn and winter. A simple 25-hydroxyvitamin D blood test shows whether your level is low.
Why Vitamin D Matters
Vitamin D, often called the "sunshine vitamin", helps the body absorb calcium and phosphate from food. These minerals are needed for healthy bones, teeth and muscles. Most of our vitamin D is made in the skin when it is exposed to sunlight, with smaller amounts coming from food.
Long-term deficiency can cause rickets in children and osteomalacia (soft, painful bones) in adults. It also adds to the risk of osteoporosis and fractures in later life.
UK Guidelines and Reference Ranges
In the UK, guidance comes from the Scientific Advisory Committee on Nutrition (SACN), the NHS and the National Institute for Health and Care Excellence (NICE). Your vitamin D status is measured as serum 25-hydroxyvitamin D (25(OH)D):
UK reference ranges (SACN, NICE CKS and the Royal Osteoporosis Society). These are what most UK labs report against, for all ages and both sexes.
| Status | nmol/L | ng/mL |
| Deficient | Below 25 | Below 10 |
| Possibly inadequate in some people | 25–50 | 10–20 |
| Sufficient for almost everyone | Above 50 | Above 20 |
| Toxicity concern (usually with high calcium) | Above 250 | Above 100 |
To convert, divide nmol/L by 2.5 to get ng/mL.
NHS supplement advice:
- Everyone, including pregnant and breastfeeding women, should consider a daily supplement of 10 micrograms (400 IU) of vitamin D between October and March.
- People at higher risk of deficiency (see below) are advised to take 10 micrograms a day all year round.
- Breastfed babies from birth to 1 year should have a daily supplement of 8.5 to 10 micrograms. Babies having more than 500 ml of infant formula a day do not need one, as formula is already fortified.
- Children aged 1 to 4 should have a daily 10 microgram supplement all year round.
- Most adults should not take more than 100 micrograms (4,000 IU) a day unless a doctor advises it.
Watch our short video: Why the UK sun is too weak for vitamin D from October to early March (45 seconds, E&J Bio on TikTok)
You can read more on the NHS vitamin D page.
Common Symptoms of Vitamin D Deficiency
Many people with low vitamin D have no symptoms. When symptoms do occur, they are often vague. Common signs include:
- Tiredness and low energy
- Bone pain or aching, often in the lower back, hips, legs or ribs
- Muscle aches, cramps or weakness, such as difficulty climbing stairs or rising from a chair
- Low mood
- Frequent infections in some people
In severe cases, deficiency can cause rickets in children (bowed legs, delayed growth, dental problems) and osteomalacia in adults (soft bones and fractures).
Who Is at Risk?
Some groups are more likely to have low vitamin D:
- People who are rarely outdoors, such as those who are frail, housebound or living in a care home
- People who usually cover most of their skin when outside
- People with dark skin, for example those of African, African-Caribbean or South Asian background, who need more sun to make the same amount of vitamin D
- Older adults, as the skin makes less vitamin D with age
- Pregnant and breastfeeding women, babies and young children
- People living with obesity
- People with conditions that affect fat absorption, such as coeliac disease, Crohn's disease or after weight-loss surgery
- People with liver or kidney disease, or taking certain medicines such as some anti-epilepsy drugs
How Is Vitamin D Deficiency Diagnosed?
Diagnosis is made with a blood test that measures serum 25-hydroxyvitamin D (25(OH)D), the main circulating form of vitamin D and the best marker of your vitamin D status. At E&J Bio you can book a Vitamin D (25-OH) test.
Your doctor may also check other related tests, including:
- Bone profile: calcium, phosphate, albumin and alkaline phosphatase (ALP)
- Parathyroid hormone (PTH), if calcium is abnormal
- Kidney function (U&Es and eGFR)
- Liver function tests
Treatment and Prevention
Treatment depends on how low your level is and should be guided by a healthcare professional. For adults with deficiency (below 25 nmol/L, or 10 ng/mL), NICE guidance describes a loading course totalling about 300,000 IU over 6 to 10 weeks, for example:
- 50,000 IU once a week for 6 weeks
- 20,000 IU twice a week for 7 weeks
- 4,000 IU daily for 10 weeks
This is usually followed by a maintenance dose of 800 to 2,000 IU a day, starting about one month after the loading course ends. Where a quick correction is not needed, a maintenance dose alone may be used.
For insufficiency (25–50 nmol/L, or 10–20 ng/mL), a daily supplement of 800 to 2,000 IU is often advised, especially for people with risk factors. Everyday measures that help include:
- Short periods of sun on bare skin (forearms, hands or lower legs) between late March and the end of September, taking care not to burn
- Eating oily fish such as salmon, mackerel, sardines and herring
- Including eggs, red meat and fortified foods such as some breakfast cereals and fat spreads
- Taking a 10 microgram daily supplement from October to March, or all year if you are in a higher-risk group
Clinical Pearl: Check serum calcium before starting high-dose vitamin D, as deficiency can mask primary hyperparathyroidism and treatment may then reveal high calcium. Recheck calcium about a month after a loading course, and consider rechecking 25(OH)D after about 3 months if symptoms continue or absorption is a concern.
When to Seek Help
If you have ongoing tiredness, bone pain or muscle weakness, speak to your GP. They may arrange a vitamin D test and other blood tests to look for a cause.
Remember: taking high-dose vitamin D without testing or medical advice can be harmful, as too much can raise calcium levels. Seek advice before starting high-dose supplements, especially if you have kidney disease, kidney stones, sarcoidosis or take thiazide diuretics.
Conclusion
Vitamin D deficiency is common in the UK, especially in winter, but it is easy to test for and treat. Knowing the NHS advice, recognising the symptoms and understanding your risk factors are key steps. If you think your level may be low, get tested and follow evidence-based advice.
Book a Vitamin D Test at E&J Bio
Walk-ins are welcome at our clinic at 305 Neasden Lane, London NW10 1QR. We are open 7 days a week, including Sundays, or you can book online at ejbio.co.uk/shop.
- Vitamin D (25-OH)
- Full Body MOT Health Check (includes vitamin D, calcium and bone markers)
This article is for general information only. Please discuss your results, and any symptoms, with a doctor or other qualified healthcare professional.