Vitamin D deficiency symptoms UK: what your blood test shows.

Vitamin D deficiency is one of the most common nutritional deficiencies in the UK. The country's latitude means that for roughly six months of the year, October to March, the sun is too low in the sky to trigger meaningful vitamin D synthesis in the skin. Public Health England recommends that everyone in the UK consider supplementing during this period.

UK reference ranges for vitamin D, 25-OH-D.

Vitamin D is measured as 25-hydroxyvitamin D in the blood. UK labs report in nmol/L:

Classification by level

Level, nmol/L	Classification	What it means
Below 25	Severe deficiency	Risk of rickets in children and osteomalacia in adults. Significant health impact.
25 to 49	Deficiency	NHS threshold for deficiency. Supplementation is typically recommended.
50 to 74	Insufficient	Below optimal. Many experts recommend supplementing to above 75.
75 to 200	Sufficient	Generally considered adequate. The optimal range is debated.
Above 250	Potentially toxic	Rare from diet or sun. Possible with very high dose supplementation.

Symptoms of vitamin D deficiency.

Vitamin D deficiency can be entirely without symptoms, particularly when mild. When symptoms do occur, they are often vague and easy to attribute to other causes:

• Fatigue and low energy. One of the most commonly reported symptoms.
• Bone pain and muscle aches. Particularly in the back, hips and legs.
• Muscle weakness. Difficulty climbing stairs or rising from a chair.
• Low mood. Vitamin D receptors are present in brain tissue, and deficiency is associated with seasonal low mood.
• Frequent infections. Vitamin D plays a role in immune function.
• Hair loss. Some evidence links severe deficiency to alopecia areata.
• Slow wound healing.

Who is most at risk in the UK?

• People with darker skin tones, as melanin reduces UV absorption
• Those who cover most of their skin for cultural or medical reasons
• People who spend little time outdoors
• Adults over 65, as skin becomes less efficient at making vitamin D
• People with obesity, as vitamin D can be held in fat tissue rather than circulating
• Those with malabsorption conditions such as Crohn's or coeliac disease
• Exclusively breastfed infants

NHS supplementation guidance.

The NHS recommends 10 micrograms, 400 IU, of vitamin D daily for adults and children over 4 during autumn and winter. For those at higher risk, or confirmed deficient by blood test, a GP may prescribe higher doses: typically 800 to 3,000 IU daily, or a loading dose for severe deficiency.

Vitamin D3, cholecalciferol, is generally preferred over D2 as it is more effective at raising blood levels. Taking it with a meal containing fat improves absorption, as vitamin D dissolves in fat.

Monitoring after supplementation.

If you are supplementing at higher doses, it is worth retesting after three to four months to confirm your levels have responded. Vitamin D toxicity is rare but possible with very high doses over prolonged periods. Symptoms include nausea, weakness and high blood calcium.

What to ask your GP.

• What is my vitamin D level, and does it explain my symptoms?
• What dose do you recommend, and for how long?
• Should I retest after supplementing, and when?
• Is there any reason I might not be absorbing vitamin D normally?