Vitamin D Deficiency in the UK: Symptoms, Causes, and How to Fix It

You feel tired all the time. Your muscles ache for no obvious reason. You catch every cold going. Sound familiar? These vague, easy-to-dismiss complaints are among the most common signs of vitamin D deficiency — a condition that affects roughly one in five UK adults, according to the Scientific Advisory Committee on Nutrition (SACN).

The problem is that vitamin D deficiency creeps up slowly. There's no dramatic moment when you realise something is wrong. Instead, you adapt to feeling slightly below par until that becomes your new normal. Let's change that.

How Common Is Vitamin D Deficiency in the UK?

Very common. Government data show that approximately 20% of adults and 16% of children in the UK have serum vitamin D levels below 25 nmol/L — the threshold for deficiency. During winter and spring, that figure climbs significantly because the UK sits too far north (above latitude 52°N) for our skin to produce meaningful vitamin D from sunlight between October and March.

The SACN report confirmed that the UK's climate makes it essentially impossible to maintain adequate vitamin D from sun exposure alone during half the year. That's not a fringe opinion — it's the scientific basis behind Public Health England's recommendation that every UK adult consider supplementation during autumn and winter.

Even in summer, many people fall short. Office workers, people who cover their skin for cultural or religious reasons, and anyone who diligently applies sunscreen all year round are at risk regardless of the season.

Symptoms of Vitamin D Deficiency

Vitamin D deficiency doesn't announce itself with a single unmistakable symptom. Instead, it tends to produce a cluster of complaints that are easy to blame on stress, ageing, or a busy lifestyle:

• Persistent fatigue and tiredness — feeling drained despite adequate sleep
• Bone and joint pain — particularly in the lower back, hips, and legs
• Muscle weakness — difficulty with stairs, getting up from a chair, or general heaviness
• Frequent infections — catching colds, flu, and respiratory infections more often than usual
• Low mood or depression — particularly in winter months
• Slow wound healing — cuts and bruises that take longer than expected to resolve
• Hair thinning or loss — though many other causes exist, low vitamin D is worth investigating

In severe, prolonged deficiency, adults can develop osteomalacia — a softening of the bones that causes deep bone pain and muscle weakness. Children with severe deficiency may develop rickets, though this is now rare in the UK.

Practical takeaway: If you recognise three or more of these symptoms, particularly during winter, a simple blood test can confirm or rule out vitamin D deficiency within days.

Who's at Risk?

While anyone in the UK can become vitamin D deficient, certain groups are at significantly higher risk:

• People with darker skin — higher melanin levels reduce the skin's ability to produce vitamin D from sunlight. People of African, Afro-Caribbean, and South Asian heritage need considerably more sun exposure to produce the same amount
• People who spend most of their time indoors — including care home residents, shift workers, and those who are housebound
• People who cover most of their skin — for cultural, religious, or personal reasons
• Older adults — the skin's capacity to synthesise vitamin D declines with age, and older people tend to spend less time outdoors
• Pregnant and breastfeeding women — higher demand for vitamin D to support fetal bone development
• People who are overweight or obese — vitamin D is fat-soluble and gets sequestered in adipose tissue, reducing circulating levels
• People with malabsorption conditions — coeliac disease, Crohn's disease, and other gut conditions can impair vitamin D absorption

NICE guidance specifically recommends that at-risk groups take a daily vitamin D supplement all year round, not just during winter.

How to Test Your Vitamin D

The standard test measures 25-hydroxyvitamin D (also written as 25(OH)D) in your blood. This is the main circulating form of vitamin D and gives the most accurate picture of your overall vitamin D status.

The NHS does not routinely test vitamin D unless you present with symptoms suggestive of deficiency or have a condition that puts you at high risk. If you want a proactive check — particularly if you fall into one of the at-risk groups above — a private blood test is the fastest route.

A simple venous blood draw or finger-prick sample is all that's needed. Results are typically reported in nmol/L (the standard UK unit).

Normal vs Optimal Vitamin D Levels

Not all "normal" results are created equal. Here's how to interpret your number:

Level (nmol/L)	Classification	What It Means
Below 25	Deficient	Significant health risk; treatment required
25–50	Insufficient	Suboptimal; supplementation recommended
50–75	Adequate	Meets basic needs for most people
75–150	Optimal	Associated with best health outcomes
Above 150	Potentially excessive	Risk of toxicity; medical review advised

The NHS considers levels above 25 nmol/L as sufficient to prevent bone disease, but many clinicians and researchers argue that 50–75 nmol/L should be the minimum target for overall health, and levels of 75–100 nmol/L are associated with the best outcomes for immune function, mood, and musculoskeletal health.

Practical takeaway: A result of 30 nmol/L is technically "above the deficiency threshold" but is far from optimal. Don't accept "normal" at face value — look at where you sit within the range.

Treatment and Supplements

Standard supplementation

The NHS and SACN recommend that all UK adults take a daily supplement containing 10 micrograms (400 IU) of vitamin D during autumn and winter. At-risk groups should take this dose year-round.

However, if blood testing reveals that you're already deficient, 400 IU daily is unlikely to be enough to restore your levels. Your doctor may recommend a loading dose — a higher amount taken over several weeks to bring levels up — followed by a maintenance dose.

Common supplementation protocols for deficiency

• Mild deficiency (25–50 nmol/L): 1,000–2,000 IU daily for 8–12 weeks, then retest
• Moderate to severe deficiency (below 25 nmol/L): Loading dose of 50,000 IU weekly for 6 weeks, or equivalent daily high-dose regimen, followed by maintenance of 1,000–2,000 IU daily
• Maintenance after correction: 800–1,000 IU daily ongoing, adjusted based on retesting

Choosing the right supplement

Vitamin D3 (cholecalciferol) is the preferred form. It's more effective at raising and maintaining blood levels than vitamin D2 (ergocalciferol). Look for supplements that are labelled as D3.

Taking your supplement with a meal that contains fat improves absorption, since vitamin D is fat-soluble.

Dietary sources

Food alone rarely provides enough vitamin D, but helpful sources include oily fish (salmon, mackerel, sardines), egg yolks, fortified cereals and plant milks, and liver (though pregnant women should avoid liver).

Sun exposure

Between April and September, spending 10–15 minutes in direct midday sunlight with forearms and lower legs exposed several times a week can help maintain levels. However, the body self-regulates production, and longer exposure increases skin cancer risk without producing more vitamin D.

Practical takeaway: Supplementation is the most reliable way to maintain adequate vitamin D in the UK. Test, supplement, and retest after 8–12 weeks to confirm your levels have improved.

When to See a Doctor

Most people with mild vitamin D deficiency can self-manage with over-the-counter supplements and periodic testing. However, you should consult a doctor if:

• Your levels are below 25 nmol/L (you may need a prescription-strength loading dose)
• You have symptoms of osteomalacia — deep bone pain, muscle weakness, difficulty walking
• You have a malabsorption condition that may impair vitamin D uptake
• You're taking medications that interact with vitamin D metabolism (certain anticonvulsants, glucocorticoids, or weight-loss drugs)
• Your levels haven't improved after 12 weeks of appropriate supplementation
• You're pregnant or breastfeeding and unsure about safe dosing

Vitamin D deficiency is eminently fixable, but it does require attention. Left uncorrected, it quietly undermines your bones, your immune system, and your energy levels year after year. A five-minute blood test and a daily supplement are all it takes to change course.

Explore Our Tests

Want to learn more? Browse our range of health tests to find the right one for you.