Vitamin D is essential for bone health and immune function, yet many people in the UK are unsure what their vitamin D count should be. In the UK, vitamin D is measured as serum 25-hydroxyvitamin D in nanomoles per litre (nmol/L). According to NHS and NICE guidance, a level of 50 nmol/L or above is considered sufficient for most adults, whilst levels below 25 nmol/L indicate deficiency requiring treatment. Understanding your target range helps you maintain optimal health through appropriate sun exposure, diet, and supplementation, particularly during autumn and winter months when natural synthesis is limited.

What Should Your Vitamin D Level Be?

Vitamin D is measured in nanomoles per litre (nmol/L) in the UK, and understanding the recommended range is essential for maintaining bone health and supporting immune function. According to UK Government advice (formerly Public Health England) and NICE guidance, serum 25-hydroxyvitamin D (25(OH)D) is the standard biomarker used to assess vitamin D status, as it reflects both dietary intake and synthesis in the skin following sun exposure.

The UK recommended target levels are:

• Sufficient: 50 nmol/L or above

• Deficient: Below 25 nmol/L

• Insufficient: Between 25–50 nmol/L

Clinical experts agree that maintaining levels at or above 50 nmol/L provides adequate protection for musculoskeletal health in the general population. UK guidance does not recommend aiming for levels above this threshold for the general population, though research continues in this area.

It is important to note that vitamin D requirements may vary depending on individual circumstances. People with darker skin, those who are housebound or cover their skin for cultural reasons, and individuals with malabsorption conditions should consider year-round supplementation with the standard 10 micrograms (400 IU) daily dose. Pregnant and breastfeeding women, older adults, and those with chronic kidney disease also warrant particular attention to vitamin D status.

The NHS recommends that everyone in the UK should consider taking a daily supplement containing 10 micrograms (400 IU) of vitamin D during autumn and winter months when sunlight exposure is insufficient for adequate synthesis. Some individuals may benefit from year-round supplementation based on their risk factors and lifestyle. Higher doses should only be used to treat confirmed deficiency under medical supervision, and adults should not exceed 100 micrograms (4,000 IU) daily without medical advice (lower limits apply for children and infants).

Understanding Vitamin D Blood Test Results

Vitamin D blood tests measure 25-hydroxyvitamin D concentration, which is the most accurate indicator of your body's vitamin D stores. This test is typically requested by your GP when there are clinical concerns about deficiency, such as unexplained bone pain, frequent fractures, or conditions affecting vitamin D absorption. The test involves a simple blood sample, usually taken from a vein in your arm, and results are generally available within a few days to weeks, depending on your local laboratory.

Interpreting your results requires understanding the clinical thresholds. A result below 25 nmol/L indicates vitamin D deficiency and typically warrants treatment with higher-dose supplementation, often prescribed as colecalciferol (vitamin D3). Standard UK treatment regimens for deficiency often involve loading doses totalling approximately 300,000 IU over 6-10 weeks, followed by maintenance therapy of 800-2,000 IU daily. Your GP should check your adjusted serum calcium before treatment and about one month after starting high-dose therapy to monitor for hypercalcaemia. Vitamin D levels may be rechecked after about three months if clinically indicated.

When results show levels above 50 nmol/L, this generally indicates sufficiency, though your doctor will interpret this in the context of your symptoms and medical history. It is worth noting that vitamin D testing is not routinely offered to everyone, as UK health authorities recommend a population-wide supplementation approach rather than widespread screening. Testing is reserved for those with specific risk factors or clinical indications.

If you receive abnormal results, your GP will discuss appropriate management strategies. This may include prescription-strength vitamin D supplements, investigation of underlying causes such as malabsorption disorders, and monitoring of calcium levels, as vitamin D plays a crucial role in calcium metabolism. Special caution is needed in chronic kidney disease (which may require active vitamin D analogues), granulomatous diseases like sarcoidosis, and primary hyperparathyroidism—specialist advice may be needed in these cases. Never attempt to self-treat significantly low vitamin D levels without medical supervision, as appropriate dosing and monitoring are essential for safe correction of deficiency.

Symptoms of Low and High Vitamin D Levels

Vitamin D deficiency can manifest in various ways, though symptoms are often non-specific and may develop gradually over time. The most recognised consequence of severe, prolonged deficiency is impaired bone mineralisation, leading to rickets in children and osteomalacia in adults. Common symptoms of low vitamin D include persistent bone or muscle pain, particularly in the lower back, pelvis, and legs, along with muscle weakness that may affect mobility and increase fall risk in older adults.

Some people with deficiency may also experience:

• Fatigue and general tiredness, though this has many possible causes

• More frequent infections, though the association with vitamin D is not definitively established

• Low mood, particularly during winter months, though this relationship is complex

• Hair loss and impaired wound healing have been associated with deficiency in some studies, but evidence is limited

It is important to recognise that many people with vitamin D deficiency experience no obvious symptoms, which is why at-risk groups should consider supplementation regardless of how they feel. If you experience unexplained bone pain, muscle weakness, or frequent fractures, contact your GP for assessment, as these may indicate significant deficiency requiring investigation and treatment.

Vitamin D toxicity (hypervitaminosis D) is rare but can occur with excessive supplementation, typically from taking very high doses over prolonged periods. Sun exposure does not cause vitamin D toxicity. Symptoms of vitamin D excess include nausea, vomiting, weakness, and frequent urination. The most serious consequence is hypercalcaemia (elevated blood calcium), which can cause confusion, kidney stones, and cardiac arrhythmias.

Toxicity is often associated with serum levels exceeding 375 nmol/L, though adverse effects can occur at lower levels in susceptible individuals. This underscores the importance of not exceeding recommended doses without medical supervision. Adults should not take more than 100 micrograms (4,000 IU) daily, with lower limits for children (50 micrograms/2,000 IU for ages 1-10) and infants (25 micrograms/1,000 IU). If you develop persistent nausea, excessive thirst, confusion, or severe vomiting while taking vitamin D supplements, seek urgent medical attention via your GP, NHS 111, or A&E for severe symptoms, as these may indicate dangerous hypercalcaemia requiring immediate treatment.

How to Maintain Healthy Vitamin D Levels

Maintaining adequate vitamin D levels requires a balanced approach combining sensible sun exposure, dietary sources, and supplementation when necessary. In the UK, sunlight exposure between late March and September can provide sufficient vitamin D for most people. The skin synthesises vitamin D when exposed to UVB radiation, with short, frequent exposures to summer sun without burning generally being sufficient. However, this varies considerably depending on skin tone, with individuals of African, African-Caribbean, and South Asian origin requiring more sun exposure to produce the same amount of vitamin D.

It is important to balance sun exposure with skin cancer prevention. Never allow your skin to burn, and follow sun safety guidance during peak UV hours. For those unable to obtain adequate sun exposure due to lifestyle, health conditions, or cultural practices, supplementation becomes particularly important.

Dietary sources of vitamin D include:

• Oily fish such as salmon, mackerel, sardines, and herring

• Egg yolks

• Fortified foods including breakfast cereals, fat spreads, and some plant-based milk alternatives

• Red meat and liver in smaller amounts

However, it is difficult to obtain sufficient vitamin D from diet alone, which is why UK health authorities recommend that everyone should consider taking a daily supplement containing 10 micrograms (400 IU) of vitamin D, particularly during autumn and winter.

For those at higher risk of deficiency, year-round supplementation is advisable. This includes people who are housebound, residents in care homes, those who cover their skin for cultural or religious reasons, and individuals with darker skin. If you have conditions affecting fat absorption, such as Crohn's disease, coeliac disease, or have undergone bariatric surgery, discuss appropriate supplementation doses with your GP, as you may require higher amounts.

When choosing supplements, vitamin D3 (colecalciferol) is generally preferred over vitamin D2 (ergocalciferol) as it is more effective at raising blood levels. Supplements are widely available without prescription and are generally safe when taken at recommended doses. Adults should not exceed 100 micrograms (4,000 IU) daily without medical supervision. Pregnant women should avoid cod liver oil supplements due to their vitamin A content.

Vitamin D can interact with several medications, including thiazide diuretics, digoxin, orlistat, cholestyramine, rifampicin, and some anticonvulsants. If you are taking other medications, have kidney disease, sarcoidosis or other granulomatous conditions, consult your GP or pharmacist before starting supplementation. Report any suspected side effects from prescribed vitamin D via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

Frequently Asked Questions