Vitamin D plays a role in bone health, immune function and mood regulation, but it's also one of the easiest nutrients to become deficient in, particularly in the UK where sunlight, the main natural source, is limited for much of the year.
Signs of low vitamin D
- Fatigue or low energy that doesn't improve with rest
- Bone or muscle aches
- Getting ill more often than usual
- Low mood, particularly over autumn and winter
- Hair thinning in more significant deficiency
These symptoms overlap with a lot of other conditions, which is exactly why testing is more useful than guessing.
How a vitamin D test works
1. Order your test kit
2. Take a small finger-prick blood sample at home
3. Return it in the prepaid packaging
4. Receive your result online, measured in nmol/L (the UK standard unit)
Understanding your result
In the UK, vitamin D levels are generally categorised as:
Deficient: levels low enough to warrant supplementation and, in some cases, a GP conversation
Insufficient: below optimal but not severely low, often improved with diet, sensible sun exposure and supplementation
Sufficient: within a healthy range for most people
Your results will come with the specific reference ranges used, since exact thresholds can vary slightly between laboratories and guidelines.
Who's most at risk of deficiency?
- People who spend most of their time indoors
- Those with darker skin, which needs more sun exposure to produce the same amount of vitamin D
- Older adults
- People who consistently cover most of their skin outdoors
- Anyone during the autumn and winter months in the UK, when sunlight is too weak for the body to produce vitamin D regardless of time outside
What to do if you're deficient
Most people can improve their levels with a daily vitamin D supplement, along with safe sun exposure in the warmer months and vitamin D-rich foods like oily fish and fortified products. If your levels are significantly low, or you have symptoms like persistent bone pain, it's worth discussing your results with a GP, who may recommend a higher-dose, medically supervised course of supplementation.
