Low Vitamin D and Tiredness: What Your Levels Mean
Short answer: very low vitamin D can contribute to tiredness, muscle weakness and aches, and it is common in the UK, especially in winter. A blood level below 25 nmol/L is treated as deficient. But tiredness has many causes, so it is worth checking iron, thyroid and blood count at the same time.
What vitamin D levels mean
Below 25 nmol/L: deficient
25 to 50 nmol/L: may be inadequate for some people
Above 50 nmol/L: sufficient for almost everyone
These are the thresholds generally used in UK guidance. Some laboratories print different ranges, so use the range on your own report.
Who is more likely to be low
Anyone in the UK between October and March, people who spend little time outdoors or cover their skin, people with darker skin, older adults, people living with obesity, and people with conditions that affect absorption, such as coeliac disease.
Prevention and treatment
The NHS advises everyone in the UK to consider a daily 10 microgram (400 IU) vitamin D supplement in autumn and winter, and all year round if they are at higher risk. A confirmed deficiency is usually treated with a higher-dose course for several weeks, followed by a maintenance dose. Do not take high doses long term without advice, because too much vitamin D can raise calcium levels.
Tired all the time? Check more than vitamin D
Low iron stores, an underactive thyroid, anaemia, low B12 and blood sugar problems all cause tiredness. Testing them together saves repeat visits. See low ferritin explained and how to read your blood test results.
How we can help
Book a vitamin D blood test on its own or as part of a wider health check. If your result is low, or you are still tired despite normal results, book a private clinician consultation with our Advanced Clinical Practitioner, by phone UK-wide from £50 or face to face in Crewe. A prescription is included if you need one.
Frequently asked questions
How long does it take to feel better after starting vitamin D?
Levels usually rise over several weeks of treatment. If you do not feel better once your level is normal, another cause should be looked for.
When should I retest?
Routine retesting is not always needed. If you have been treated for deficiency, a recheck after about three months, or as your clinician advises, confirms your level has recovered.
This article is general information based on UK guidance from the NHS and NICE. It is not personal medical advice. If you are worried about your health, speak to a clinician.
