Vitamin D deficiency is extremely common in the UK, with an estimated 1 in 5 people having low vitamin D levels. Unlike most nutrients, vitamin D is primarily produced by the skin in response to sunlight rather than obtained through food alone. The UK’s northerly latitude and often overcast weather means that between October and March, sunlight is not strong enough for the skin to make vitamin D — making deficiency almost universal during these months.
What Is Vitamin D and Why Do We Need It?
Vitamin D is a fat-soluble vitamin that functions more like a hormone in the body. It plays a critical role in calcium and phosphate absorption, which are essential for maintaining healthy bones, teeth, and muscles. Vitamin D also supports immune function, has anti-inflammatory effects, influences mood regulation and mental health, and is involved in cell growth and cardiovascular health.
Severe vitamin D deficiency causes rickets in children (soft, weak bones) and osteomalacia in adults (bone pain and muscle weakness). Chronic low-level deficiency is associated with increased risk of osteoporosis, fractures, depression, autoimmune conditions, cardiovascular disease, and certain cancers.
Vitamin D Deficiency Symptoms
Many people with low vitamin D levels have no obvious symptoms, or the symptoms are vague and easily attributed to other causes. Common symptoms of vitamin D deficiency include persistent tiredness and fatigue, bone pain or tenderness particularly in the back, hips, and legs; muscle weakness or aches, frequent infections and illnesses, low mood and depression, hair loss, and in children, delayed growth and skeletal deformities.
Because these symptoms overlap with many other conditions, the only way to confirm vitamin D deficiency is through a blood test measuring 25-hydroxyvitamin D levels. Your GP can arrange this test, though it is not routinely offered to everyone. Many people opt for a private blood test, which is available for around £25–£40 through various UK laboratories.
Who Is Most at Risk of Vitamin D Deficiency in the UK?
Certain groups are at particularly high risk of vitamin D deficiency in the UK. People with darker skin tones (South Asian, African, African-Caribbean, and Middle Eastern backgrounds) require more sunlight exposure to produce the same amount of vitamin D as those with lighter skin, making deficiency more common. Other high-risk groups include people who cover most of their skin for cultural or religious reasons, people who spend little time outdoors, people over 65 (as the skin becomes less efficient at producing vitamin D with age), babies and young children (particularly if breastfed, as breast milk is low in vitamin D), pregnant and breastfeeding women, people who are obese (as vitamin D is stored in fat tissue and becomes less available), people with conditions affecting fat absorption such as Crohn’s disease, coeliac disease, and cystic fibrosis, and people in care homes or who are housebound.
NHS Vitamin D Recommendations
The NHS recommends that everyone in the UK consider taking a daily vitamin D supplement of 10 micrograms (400 IU) during autumn and winter (October to March). People who are at high risk — including those in the at-risk groups listed above — are advised to take a supplement year-round. The NHS specifically advises that babies from birth to one year should receive a daily supplement of 8.5–10 micrograms of vitamin D unless they are consuming more than 500ml of formula per day (which is already fortified).
NHS vitamin D supplements are available for free through the Healthy Start scheme for eligible pregnant women, new mothers, and families with children under four. Vitamin D supplements are also widely available from pharmacies, supermarkets, and health food shops at low cost.
Vitamin D Blood Test Levels: What Do the Numbers Mean?
| 25-Hydroxyvitamin D Level (nmol/L) | Status |
|---|---|
| Below 25 nmol/L | Deficient — treatment required |
| 25–49 nmol/L | Insufficient — supplementation advised |
| 50–75 nmol/L | Adequate for most people |
| 75–200 nmol/L | Optimal range |
| Above 250 nmol/L | Potentially toxic — risk of hypercalcaemia |
Vitamin D Food Sources
Few foods naturally contain significant amounts of vitamin D, which is why sunlight and supplementation are so important in the UK. The best dietary sources include oily fish such as salmon, mackerel, herring, sardines, and pilchards; cod liver oil; egg yolks; red meat and liver; and fortified foods including some breakfast cereals, dairy alternatives (oat milk, soya milk), margarine, and some dairy products.
Wild mushrooms exposed to sunlight contain vitamin D2 and can contribute to intake, particularly useful for people following a vegan diet. UV-exposed mushrooms are now available in some UK supermarkets.
Vitamin D Supplements: What to Look For
When choosing a vitamin D supplement, look for vitamin D3 (cholecalciferol) rather than D2 (ergocalciferol), as D3 is more effective at raising blood levels. A daily dose of 10 micrograms (400 IU) is recommended for general prevention, while people with confirmed deficiency may be prescribed higher doses (typically 1,000–4,000 IU daily) by their GP. The NHS advises not to exceed 100 micrograms (4,000 IU) per day without medical supervision, as very high doses can be harmful over time. Vegan vitamin D3 derived from lichen is available for those who avoid animal products.
Vitamin D, Mood and Mental Health
There is a well-established association between low vitamin D levels and depression, seasonal affective disorder (SAD), and low mood. The UK’s long, dark winters mean many people experience worsening mood during winter months, and some research suggests that vitamin D supplementation may help improve mood in those who are deficient. However, vitamin D supplements alone are not a treatment for depression, and anyone experiencing significant low mood should speak to their GP.
Important: If you think you may be vitamin D deficient, speak to your GP before taking high-dose supplements. Very high vitamin D intake can cause hypercalcaemia (too much calcium in the blood), which can lead to nausea, weakness, kidney problems, and in severe cases, heart arrhythmias.
Related Health Guides on YourHealthXpert
Explore these related NHS-aligned health guides on conditions connected to this topic:
- Osteoporosis — vitamin D is essential for calcium absorption and bone health
- Anxiety and Depression — low vitamin D is associated with depression, particularly in winter
- Type 2 Diabetes — vitamin D deficiency is common in people with type 2 diabetes
- Fatigue — vitamin D deficiency is a very common and treatable cause of tiredness
- Iron Deficiency Anaemia — another common nutritional deficiency causing fatigue