Vitamin deficiency: symptoms, causes, testing and treatment

• What is a vitamin deficiency?
• Why do vitamin deficiencies happen?
• The top 8 most common vitamin deficiencies
• Worried you may have vitamin deficiencies?
• How are vitamin deficiencies diagnosed?
• Can vitamin deficiency be reversed?
• FAQs about vitamin deficiency
• Conclusion: why vitamin deficiency matters

Ever wondered why you’re tired all the time, have brittle nails, or seem to catch every cold going around? You might be dealing with a vitamin deficiency. Despite our best efforts to eat well, vitamin deficiency is surprisingly common in the UK, and it can sneak up on anyone, regardless of age, diet, or lifestyle. The good news? Most vitamin deficiencies are easily treatable once you know what to look for.

In this guide, we’ll explore what vitamin deficiency actually means, why it happens, how to spot the symptoms, and what you can do to get back on track. We’ll cover the eight most common vitamin deficiencies, highlight what each vitamin does, the signs you could be running low, and the best ways to test and treat them.

What is a vitamin deficiency?

A vitamin deficiency occurs when your body doesn’t get enough of a particular vitamin to function properly. Vitamins are essential nutrients that play vital roles in everything from bone health to energy production and immune defence. Without enough, you can experience a wide range of symptoms, some subtle, others more dramatic.

Why do vitamin deficiencies happen?

Vitamin deficiencies can strike for all sorts of reasons. Here are the usual suspects:

1. Poor diet: Not enough fruit, veg, wholegrains, or dairy.
2. Restricted diets: Vegan, vegetarian, or exclusion diets can limit certain vitamins.
3. Digestive issues: Conditions like coeliac disease or Crohn’s can affect absorption.
4. Medical conditions: Kidney or liver problems, or certain medications.
5. Lifestyle factors: Smoking, alcohol, or lack of sunlight (classic British winter!).
6. Age: Older adults may absorb some vitamins less efficiently.

The top 8 most common vitamin deficiencies

Let’s break down the eight vitamin deficiencies most frequently searched for in the UK.

1. Vitamin D deficiency

Vitamin D is known as the “sunshine vitamin” because our bodies produce it when exposed to sunlight. It’s technically a hormone precursor and is found in a small number of foods, like oily fish, eggs, and fortified products. Vitamin D helps the body absorb calcium and phosphate, keeping bones, teeth, and muscles healthy. It also supports immune function and may influence mood.

A blood level of 50 nmol/L or above is considered sufficient in the UK; below 30 nmol/L is deficient.

Symptoms of deficiency

1. Tiredness and low energy
2. Bone pain or muscle weakness
3. Frequent infections
4. Low mood, sometimes described as “winter blues”

Causes

1. Lack of sunlight (especially autumn/winter)
2. Darker skin (melanin reduces vitamin D production)
3. Ageing
4. Diet low in vitamin D-rich foods
5. Certain medical conditions that affect absorption

Testing and treatment

A blood test measures vitamin D levels. Treatment includes spending more time outdoors, eating vitamin D-rich foods, and taking supplements if needed. For an in-depth look, see this guide to vitamin D.

2. Vitamin B12 deficiency

Vitamin B12 (cobalamin) is a water-soluble vitamin found in animal products like meat, fish, eggs, and dairy. It’s not naturally present in plant foods. It’s essential for making healthy red blood cells, keeping your nervous system in check, and supporting DNA and energy production.

A serum B12 level above 190 pg/mL is usually considered normal, but ranges can vary by lab.

Symptoms of deficiency

1. Extreme tiredness
2. Pins and needles (paraesthesia)
3. Mouth ulcers
4. Mood changes (depression, confusion)
5. Pale or jaundiced skin

Causes

1. Vegan or vegetarian diet
2. Pernicious anaemia (an autoimmune condition)
3. Digestive disorders (e.g., Crohn’s, coeliac)
4. Certain medications (e.g., metformin, PPIs)

Testing and treatment

Diagnosed with a blood test. Treatment may involve B12 injections or high-dose oral supplements, plus dietary tweaks to include more fortified foods or animal products.

3. Folate (vitamin B9) deficiency

Folate, or vitamin B9, is a water-soluble vitamin found in green leafy veg, beans, and citrus fruits. The synthetic form, folic acid, is used in supplements and fortified foods. Folate is vital for cell growth and DNA formation, making it especially important during pregnancy and childhood. It also helps make healthy red blood cells.

Serum folate above 3 ng/mL is considered normal.

Symptoms of deficiency

1. Tiredness and weakness
2. Mouth sores or swollen tongue
3. Irritability
4. Shortness of breath
5. Poor growth in children

Causes

1. Poor diet
2. Pregnancy (higher requirements)
3. Alcohol misuse
4. Malabsorption (e.g., coeliac disease)

Testing and treatment

Diagnosed by blood test. Treatment involves increasing dietary folate and sometimes taking supplements, especially during pregnancy or for those with absorption issues.

4. Vitamin C deficiency

Vitamin C (ascorbic acid) is a water-soluble vitamin found in fruits and vegetables, especially citrus, peppers, and berries. It’s a powerful antioxidant, helps protect cells from damage, supports the immune system, and is vital for making collagen (for healthy skin, blood vessels, bones, and cartilage).

Plasma vitamin C above 23 µmol/L is considered normal.

Symptoms of deficiency

1. Fatigue and weakness
2. Bleeding gums or loose teeth
3. Poor wound healing
4. Easy bruising
5. Dry, rough skin

Causes

1. Poor intake of fruit and vegetables
2. Smoking (increases vitamin C needs)
3. Restricted diets

Testing and treatment

Diagnosis is based on symptoms and dietary history, sometimes confirmed by blood tests. Treatment is straightforward: eat more vitamin C-rich foods or take a supplement if needed.

5. Iron deficiency (anaemia)

Iron is a mineral, not a vitamin, but iron deficiency is closely linked to vitamin status (especially with B12 and folate). It’s found in red meat, beans, lentils, and leafy greens. Iron is essential for making haemoglobin, the protein in red blood cells that carries oxygen around your body. It also supports immune function, brain development, and energy production.

Serum ferritin above 30 µg/L is considered normal for adults, but ranges may vary.

Symptoms of deficiency

1. Tiredness and lack of energy
2. Shortness of breath
3. Pale skin
4. Heart palpitations
5. Brittle nails or hair loss

Causes

1. Menstruation (especially heavy periods)
2. Pregnancy
3. Poor diet
4. Blood loss
5. Malabsorption

Testing and treatment

A blood test checks haemoglobin and ferritin. Treatment involves iron supplements and dietary changes. In severe cases, further investigation for underlying causes may be needed.

6. Vitamin A deficiency

Vitamin A is a fat-soluble vitamin found in two main forms: retinol (from animal products) and carotenoids (from colourful fruits and veg). It supports good vision (especially in low light), keeps your skin and immune system healthy, and plays a role in growth and development.

Serum retinol above 1.05 µmol/L is considered normal.

Symptoms of deficiency

1. Night blindness or trouble seeing in low light
2. Dry eyes or skin
3. Frequent infections
4. Delayed growth in children

Causes

1. Poor intake of dairy, eggs, oily fish, or orange/yellow veg
2. Malabsorption conditions
3. Liver disorders

Testing and treatment

Blood tests can confirm deficiency. Treatment involves increasing dietary intake or using supplements under medical supervision, too much vitamin A can be toxic.

7. Vitamin E deficiency

Vitamin E is a group of fat-soluble compounds with powerful antioxidant properties, found in nuts, seeds, vegetable oils, and green leafy vegetables. It protects cell membranes from damage, supports immune function, and helps keep your skin and eyes healthy.

Serum alpha-tocopherol above 12 µmol/L is considered normal.

Symptoms of deficiency

1. Nerve and muscle damage (tingling, weakness)
2. Vision problems
3. Poor immune response
4. Difficulty with coordination

Causes

1. Fat malabsorption (e.g., cystic fibrosis, chronic pancreatitis)
2. Rare genetic disorders
3. Very low-fat diets

Testing and treatment

Blood tests can confirm deficiency. Treatment focuses on addressing underlying causes and supplementing vitamin E if needed, under medical guidance.

8. Vitamin K deficiency

Vitamin K is a fat-soluble vitamin found in green leafy veg (K1) and animal products/fermented foods (K2). It’s essential for blood clotting and bone health, helping your body use calcium effectively.

Plasma vitamin K1 above 0.5 ng/mL is considered normal.

Symptoms of deficiency

1. Easy bruising
2. Excessive bleeding
3. Heavy periods
4. Blood in urine or stool

Causes

1. Poor dietary intake
2. Malabsorption
3. Long-term use of antibiotics

Testing and treatment

Blood clotting tests can indicate a deficiency. Treatment involves increasing dietary vitamin K and, in severe cases, supplementation or injections.

How are vitamin deficiencies diagnosed?

Most vitamin deficiencies are picked up with a simple blood test, often after you report symptoms to your GP. Sometimes, your doctor will also ask about your diet, lifestyle, and any medications you’re taking. For some vitamins (like vitamin D), deficiency can be “silent” for a long time, so testing may be recommended even if you feel fine.

Can vitamin deficiency be reversed?

The good news is that most vitamin deficiencies can be reversed with the right approach. This usually means:

1. Eating a more balanced diet, packed with whole foods and a rainbow of fruit and veg
2. Taking supplements where needed, always under medical supervision
3. Treating any underlying health conditions that may affect absorption
4. Regular follow-up blood tests to monitor progress

In some cases, such as with vitamin B12 deficiency caused by pernicious anaemia, ongoing treatment may be required to keep levels healthy.

FAQs about vitamin deficiency