Two common vitamin D questions: is D3 better than D2, and what are the signs of low vitamin D? This guide answers both honestly — with vitamin D's authorised roles stated correctly, and a careful, GP-first approach to deficiency.
For transparency: vitamin D is a vitamin with authorised UK claims (it contributes to the maintenance of normal bones and muscle function, and to the normal function of the immune system). We use that wording. Deficiency, however, is a medical matter for your GP — not something to self-diagnose from a symptom list.
Vitamin D3 vs D2: which is better?
There are two dietary forms of vitamin D:
- Vitamin D3 (cholecalciferol) — the form your skin makes from sunlight, and the form found in animal sources. It's widely regarded as the more effective form at raising and maintaining vitamin D levels in the body.
- Vitamin D2 (ergocalciferol) — a plant/fungal-derived form, generally considered less effective at maintaining levels than D3.
For most people, D3 is the preferred choice, which is why it's the form in both our Vitamin D3 1000 IU and our D3+K2 4000 IU. (Note: most D3 is animal-derived, so strict vegans should check the source.)
What are the signs of low vitamin D?
Here we'll be careful, because this is where a lot of content overreaches. Low vitamin D is genuinely common, particularly in the UK, and is associated with non-specific signs such as tiredness, aches, and low mood. But — and this matters — these signs are vague and overlap with countless other causes, so they can't tell you that you're deficient. So-called "weird symptoms" lists circulating online can cause needless worry or false reassurance. The honest answer: you can't diagnose vitamin D deficiency from symptoms. If you're concerned, your GP can arrange a simple blood test.
Why low vitamin D is so common in the UK
Vitamin D is made in the skin from sunlight, and at UK latitudes there isn't enough strong sunlight from roughly October to March for the body to make it. This is exactly why UK health authorities advise that adults consider a daily vitamin D supplement, particularly over autumn and winter — we cover this in vitamin D in winter.
What vitamin D actually does (authorised)
Vitamin D contributes to: the maintenance of normal bones and teeth, normal muscle function, the normal function of the immune system, and normal blood calcium levels. These are the genuine, authorised roles — the honest foundation for taking it, distinct from the exaggerated cure-all claims you sometimes see.
The takeaway
D3 is the more effective form and the one to choose; the "signs" of low vitamin D are real but too non-specific to self-diagnose, so a blood test via your GP is the honest route; and UK winters are why supplementing is widely advised. Vitamin D's authorised roles cover bones, muscle and immune function. For the D3+K2 question and safe amounts, see D3 vs D3+K2 and is 4000 IU safe.
Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle. Suspected vitamin D deficiency should be assessed by your GP, who can arrange a blood test. If you are pregnant, breastfeeding, taking medication or managing a medical condition, speak to your GP or pharmacist before starting a new supplement. Signed, Dr. Miron, Founder of Pure Vitamins UK.
