Vitamin D Blood Test
Jan 29, 2026
Vitamin D Blood Test
A vitamin D blood test measures 25-hydroxyvitamin D (25-OH-D) in your blood—the most accurate way to assess your vitamin D status, with research showing 1 in 5 UK adults are deficient and up to 40% have insufficient levels. Given vitamin D's crucial role in bone health, immune function, mood, and even longevity, knowing your level is one of the most valuable tests you can do.
At Blood Test London, vitamin D testing costs from £245 with results in 2-3 days.
Understanding Vitamin D Levels
Level (nmol/L) | Status | Recommendation |
|---|---|---|
Below 25 | Deficient | High-dose supplementation needed |
25-50 | Insufficient | Supplementation recommended |
50-75 | Adequate | Maintenance dose may help |
75-150 | Optimal | Ideal range for health |
Above 150 | Potentially excessive | Reduce supplementation |
Note: Some experts recommend optimal levels of 100-150 nmol/L for disease prevention and longevity.
Why Vitamin D Matters
Bone Health
Enables calcium absorption
Prevents osteoporosis and fractures
Essential for teeth health
Immune Function
Modulates immune response
May reduce infection risk
Associated with autoimmune disease prevention
Mood and Mental Health
Linked to depression when deficient
Seasonal affective disorder connection
Supports cognitive function
Longevity and Disease Prevention
Research links adequate vitamin D to reduced risk of:
Cardiovascular disease
Type 2 diabetes
Certain cancers
All-cause mortality
Signs of Vitamin D Deficiency
Physical Symptoms
Fatigue and tiredness
Bone pain or achiness
Muscle weakness
Frequent infections
Slow wound healing
Mood Symptoms
Depression or low mood
Anxiety
Brain fog
Who's Most at Risk?
UK residents: Limited sunlight October-March
Darker skin tones: Need more sun exposure
Elderly: Reduced skin synthesis
Indoor workers: Minimal sun exposure
Obese individuals: Vitamin D trapped in fat tissue
Vegans: Limited dietary sources
How to Optimise Vitamin D
Sunlight
Best source but limited in UK
10-30 minutes midday sun on face and arms
Impossible to get enough in UK winter
Supplementation
Status | Recommended Dose |
|---|---|
Deficient (<25) | 4,000-10,000 IU daily for 8-12 weeks |
Insufficient (25-50) | 2,000-4,000 IU daily |
Maintenance | 1,000-2,000 IU daily |
Choose D3 (cholecalciferol) over D2 for better absorption.
Food Sources
Food | Vitamin D per serving |
|---|---|
Oily fish (salmon, mackerel) | 400-500 IU |
Fortified milk | 100 IU |
Egg yolk | 40 IU |
Mushrooms (UV-exposed) | 400 IU |
Reality check: Diet alone rarely provides enough.
Tips for Better Absorption
Take with fat-containing meal
Check magnesium levels (needed for activation)
Consider vitamin K2 for bone health synergy
When to Test Vitamin D
Test Now If You:
Have any deficiency symptoms
Haven't tested in the past year
Take supplements and want to check levels
Have risk factors for deficiency
Live in the UK (especially in winter)
Retest:
8-12 weeks after starting supplementation
Annually to maintain optimal levels
More frequently if adjusting doses
Book Your Vitamin D Test
Price: From £245
Results: 2-3 days
Doctor review: A doctor always reviews every result with personalised supplementation advice
Fasting required: No
FAQ
What's the best vitamin D level?
Research suggests 75-150 nmol/L is optimal for health, though the NHS considers above 50 nmol/L adequate.
Can I have too much vitamin D?
Yes, though rare. Levels above 150 nmol/L should be monitored. Toxicity typically occurs above 250 nmol/L.
How long to correct deficiency?
With proper supplementation, levels improve within 8-12 weeks.
Should I take vitamin D with other supplements?
Vitamin D works well with vitamin K2 and magnesium. Take with food for better absorption.
Do I need to test if I'm already supplementing?
Yes—testing ensures you're taking the right dose and reaching optimal levels.
Blood Test London by The Wellness. Vitamin D testing from £245, results in 2-3 days.