Ingredient
Strong evidenceVitamin D3
Also known as: vitamin D, cholecalciferol
The one supplement most people in the UK genuinely benefit from over winter.
What it is
Vitamin D is a fat-soluble vitamin your skin makes from sunlight and that supports bone health, immune function and muscle. D3 (cholecalciferol) is the form that raises blood levels most effectively. At UK latitudes there is too little sun from about October to March to make enough, so deficiency is common.
How it works
Vitamin D helps your body absorb calcium and supports immune and muscle function. Because so many people in the UK are low, especially in winter, correcting that shortfall is where the real benefit lies. As with most nutrients, more is not better once your levels are adequate.
Effective dose
UK guidance is at least 400iu (10 micrograms) a day to maintain levels, but many adults benefit from 1000 to 4000iu, particularly in winter or with limited sun exposure. Staying at or below 4000iu keeps you within the recognised safe upper limit for unsupervised use. Take it with a meal containing some fat.
Safety and upper limit
Vitamin D is safe within the usual range, but it is fat-soluble and can accumulate, so very high unsupervised doses can raise calcium too far and cause harm. If you suspect significant deficiency or want to exceed the everyday range, a simple blood test guides the right dose.
Where you find it
Standalone vitamin D3 (often with K2), multivitamins and some wellbeing blends.
Top Vitamin D picks
The highest-scoring products in the category where Vitamin D3 matters most.
Frequently asked
How much vitamin D3 should I take in the UK?
At least 400iu daily to maintain levels, with many adults benefiting from 1000 to 4000iu, especially in winter. Stay at or below 4000iu without medical supervision.
Is D3 better than D2?
Yes. Vitamin D3 (cholecalciferol) raises and maintains blood levels more effectively than D2, so it is the preferred form.
Should I take vitamin D with K2?
It is a sensible pairing, as K2 helps direct calcium into bone, but it is not essential. A well-dosed plain D3 is still very effective.
Related guides
This page is educational and not medical advice. Doses are general guidance from the published research, not a personal prescription. Before starting any supplement that could affect a medical condition or interact with medication, speak to a qualified clinician.