Vitamins & Deficiencies1 in 5 adults in the UK

Vitamin D Deficiency

Also known as: Low Vitamin D, Hypovitaminosis D

Vitamin D deficiency occurs when your body doesn't have enough vitamin D, which is essential for bone health, immune function, and overall wellbeing. It's extremely common in the UK, especially during winter months.

Last reviewed: 15 January 2026

What is Vitamin D Deficiency?

Vitamin D is a fat-soluble vitamin that your body produces when your skin is exposed to sunlight. It helps regulate calcium and phosphate in the body, which are needed to keep bones, teeth, and muscles healthy. In the UK, approximately 1 in 5 adults have low vitamin D levels.

Who is affected?

Anyone can develop vitamin D deficiency, but it's more common in people with darker skin, those who spend little time outdoors, older adults, and people who cover their skin for religious or cultural reasons.

Symptoms of Vitamin D Deficiency

Common Symptoms

  • Fatigue and tiredness
  • Bone pain or achiness
  • Muscle weakness
  • Muscle aches and cramps
  • Low mood or depression

Less Common Symptoms

  • Frequent infections
  • Slow wound healing
  • Hair loss
  • Difficulty concentrating

When to Seek Urgent Help

  • Severe bone pain
  • Difficulty walking
  • Bone fractures from minor falls

Causes & Risk Factors

Causes

  • Limited sunlight exposure (especially October-March in the UK)
  • Darker skin pigmentation (requires more sun exposure)
  • Spending most time indoors
  • Using sunscreen consistently (though sun protection is important)
  • Limited dietary intake of vitamin D
  • Malabsorption conditions affecting the gut

Risk Factors

  • Living in northern latitudes like the UK
  • Being over 65 years old
  • Having darker skin
  • Being pregnant or breastfeeding
  • Being overweight or obese
  • Having conditions affecting fat absorption
  • Taking certain medications

Possible Complications if Untreated

  • Osteomalacia (soft bones) in adults
  • Rickets in children
  • Increased risk of osteoporosis
  • Higher risk of bone fractures
  • Weakened immune system

Diagnosis & Blood Tests

Vitamin D deficiency is diagnosed through a simple blood test that measures the level of 25-hydroxyvitamin D in your blood.

Vitamin D (25-OH) Blood Test

The main test used to check vitamin D levels. Results are measured in nmol/L.

What to look for: Below 25 nmol/L is deficient, 25-50 nmol/L is insufficient, above 50 nmol/L is adequate.

Calcium Blood Test

Often checked alongside vitamin D as they work together.

What to look for: Low calcium may indicate long-term vitamin D deficiency.

Parathyroid Hormone (PTH)

May be elevated when vitamin D is low as the body tries to compensate.

What to look for: High PTH with low vitamin D suggests deficiency affecting bone health.

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Treatment Options

Treatment involves vitamin D supplementation, with the dose depending on how deficient you are.

  • Daily vitamin D supplements (usually 400-4000 IU depending on severity)
  • High-dose loading treatment for severe deficiency
  • Increasing dietary intake (oily fish, eggs, fortified foods)
  • Safe sun exposure during summer months

Living with Vitamin D Deficiency

  • Take supplements consistently, ideally with a meal containing fat for better absorption
  • Include oily fish like salmon, mackerel, and sardines in your diet
  • Choose vitamin D fortified foods like breakfast cereals and plant milks
  • Spend time outdoors during daylight hours when possible
  • Get regular blood tests to monitor your levels

Frequently Asked Questions

How much vitamin D should I take?

The NHS recommends adults and children over 4 take a 10 microgram (400 IU) supplement daily, especially during autumn and winter. If you're deficient, your doctor may recommend a higher dose temporarily.

Can I get enough vitamin D from food alone?

It's difficult in the UK. Only about 10% of our vitamin D comes from food. The main sources are oily fish, egg yolks, and fortified foods, but most people need supplements, especially in winter.

Is it possible to have too much vitamin D?

Yes, taking very high doses (usually above 4000 IU daily for extended periods) can cause vitamin D toxicity. Always follow recommended doses unless advised otherwise by your doctor.

How long does it take to correct a deficiency?

With proper supplementation, most people see improvement in symptoms within 2-3 months. Blood levels typically normalise within 2-3 months of starting treatment.

When to See Your GP

  • Persistent fatigue that doesn't improve with rest
  • Bone or muscle pain lasting more than a few weeks
  • Frequent infections or slow healing
  • Depression or low mood
  • You're at high risk and haven't had your levels checked
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