5 Signs You May Be Deficient in Vitamin D — And How to Fix It

Vitamin D is one of the most commonly deficient nutrients in the UK and Europe, particularly during the autumn and winter months when sunlight exposure drops significantly. Yet many people don't realise they're running low until symptoms become hard to ignore.

1. Persistent Fatigue

Feeling exhausted even after a full night's sleep? Low vitamin D has been linked to chronic fatigue in multiple clinical studies. Your body needs adequate vitamin D to convert food into usable energy at the cellular level.

2. Frequent Illness

Vitamin D plays a critical role in immune function. If you find yourself catching every cold that goes around, your vitamin D levels may be to blame. Research published in the British Medical Journal found that vitamin D supplementation reduced the risk of respiratory infections by up to 42% in those with the lowest baseline levels.

3. Bone and Joint Pain

Vitamin D is essential for calcium absorption. Without enough of it, your bones can become soft and weak — a condition known as osteomalacia in adults. Unexplained aches in your lower back, hips, or legs could be a red flag.

4. Low Mood or Depression

There is growing evidence linking vitamin D deficiency to mood disorders. Receptors for vitamin D are found throughout the brain, particularly in areas associated with mood regulation. Seasonal affective disorder (SAD) is partly attributed to reduced sunlight and the resulting drop in vitamin D synthesis.

5. Slow Wound Healing

If cuts and bruises take longer than usual to heal, low vitamin D could be a contributing factor. Vitamin D helps control inflammation and supports the production of compounds essential for the wound-healing process.

How to Address a Deficiency

The NHS recommends that everyone in the UK consider taking a vitamin D supplement during autumn and winter. Look for vitamin D3 (cholecalciferol), which is the form your body produces naturally from sunlight and is better absorbed than D2. A daily dose of 10-25 micrograms (400-1000 IU) is generally considered safe and effective for most adults.

Foods rich in vitamin D include oily fish (salmon, mackerel, sardines), egg yolks, and fortified foods. However, diet alone rarely provides enough — especially in northern climates.

If you suspect a deficiency, ask your GP for a blood test. Optimal serum levels are typically above 50 nmol/L, though many experts recommend 75-100 nmol/L for optimal health.