Nutrient glossary
What is vitamin D?
Vitamin D lets you absorb calcium and supports muscle and immune function; UK sunlight cannot make it from October to March.
Reviewed 20 July 2026. General information, not medical advice.
The short version
Vitamin D behaves more like a hormone than a vitamin: skin makes it from summer sunlight, and it controls how much calcium your gut absorbs, how muscles fire and how immune cells respond. From about October to March, UK sunlight is too weak for skin synthesis, which is why low status is so common here in spring.
Food alone struggles to cover it: oily fish, eggs and fortified foods are the short list. That is why UK guidance suggests everyone consider 10 µg a day from a supplement through autumn and winter.
Daily reference
10 µg a day
The reference is 10 µg (400 IU) a day. Through the darker half of the year, a supplement is the evidence-based way most people actually reach it.
This is the fixed adult reference used across these pages. In the app, your amount adjusts to your body and way of eating.
Best food sources of vitamin D
Full ranking| Food | Per serving | Per 100g |
|---|---|---|
| Trout | 24.7 µg | 19 µg |
| Salmon Fillet | 19.7 µg | 13.1 µg |
| Smoked Salmon | 9.6 µg | 17.1 µg |
| Halibut | 8.1 µg | 5.8 µg |
| Tilapia | 4.4 µg | 3.7 µg |
| Sardines (canned) | 4.4 µg | 4.8 µg |
| Whole Milk | 3.3 µg | 1.3 µg |
| Milk (semi-skimmed) | 3 µg | 1.2 µg |
Common questions
- Can I get enough vitamin D from food?
- It is hard: salmon and mackerel are the only rich everyday sources. Between October and March a 10 µg supplement is the practical route in the UK.
- What is the difference between D2 and D3?
- Both raise vitamin D status, but D3, the form from animal foods, sunlight and most supplements, raises and holds it more effectively than D2.