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

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.