Vitamin D in the UK: Do You Need a Supplement in Winter?
In the UK, the body makes most of its vitamin D from sunlight on the skin, and for roughly half the year the sun is too low for that to work well. This guide explains what vitamin D does, why autumn and winter are different, what "1000iu" means on a label, and who may need to think about it all year round.
It follows NHS guidance and the nutrition claims UK rules allow supplements to make.
What Does Vitamin D Do?
Vitamin D is a nutrient the body needs to absorb and use calcium and phosphorus. In Great Britain, the authorised health claims for vitamin D say that it contributes to:
- the normal function of the immune system
- the maintenance of normal bones
- the maintenance of normal muscle function
- the maintenance of normal teeth
- normal absorption and use of calcium and phosphorus
- normal blood calcium levels
These claims describe what vitamin D does as a nutrient. They do not mean a supplement will improve how you feel if you already get enough.
Why Is Autumn and Winter Different?
Most people in the UK can make enough vitamin D from sunlight during the spring and summer months. From around October to early spring, the sun is too low in the sky for the skin to make much, however long you spend outside. NHS guidance is that many people should consider a daily supplement containing 10 micrograms of vitamin D during autumn and winter, and that some groups should take it all year.
That is why vitamin D comes up as the clocks go back: it is the time of year when sunlight stops being a reliable source.
Who May Need It All Year?
NHS guidance says some people may not make enough vitamin D from sunlight even in summer, and should consider a daily supplement all year round. This includes people who:
- spend very little time outdoors, for example if they are housebound or live in a care home
- usually wear clothing that covers most of their skin when outside
- have dark skin, for example African, African-Caribbean or South Asian backgrounds
Other groups, including babies, young children, and people who are pregnant or breastfeeding, have their own NHS advice. If any of these apply to you, check the current NHS guidance or speak to your GP, midwife or pharmacist.
Micrograms and IU: What Does "1000iu" Mean?
Vitamin D is measured in two ways. Micrograms (µg or mcg) are used in NHS guidance, and IU (international units) are common on supplement labels. The conversion is simple: 1 microgram equals 40 IU.
- 10 micrograms is 400 IU
- 25 micrograms is 1,000 IU
So a "1000iu" supplement contains 25 micrograms. That is more than the 10 micrograms the NHS suggests as a daily amount for many people, and it is a common strength, but it is a reason to read the label. Check the amount per gummy or tablet, how many make up a serving, and do not exceed the stated daily intake. If you want to take a higher dose, or you take other supplements that contain vitamin D, speak to your GP or pharmacist.
Vitamin D2 or D3?
Supplements contain either D2 (ergocalciferol), which comes from plant sources, or D3 (cholecalciferol), which is the form the skin makes. D3 is traditionally sourced from animal sources such as sheep's wool, though vegan D3 made from lichen is also available. If you are vegetarian or vegan, check the label of any D3 product.
What About Food?
Food contributes a smaller share than sunlight, but it helps. Sources include oily fish such as salmon, sardines and mackerel, red meat, egg yolks, and fortified foods such as some breakfast cereals and spreads. Check labels, as fortification varies.
How to Choose a Vitamin D Supplement
- Amount per serving, in micrograms or IU, and what counts as a serving.
- D2 or D3, and whether it suits your diet.
- Format and extras: sugar and sweeteners in gummies, other ingredients, and allergen information.
- Cost per day, not cost per bottle.
- Directions and warnings, including the maximum daily intake.
When to Speak to a Doctor
Speak to your GP or pharmacist before taking vitamin D if you are pregnant or breastfeeding, take medication, or have a medical condition, particularly one affecting your kidneys, calcium levels or parathyroid. Do not take high doses without advice. Persistent bone or muscle pain, or other symptoms you are worried about, are a reason to see a doctor rather than self-treat. This is general information, not medical advice.
Where RISE Fits
RISE Vitamin D3 Gummies are lemon-flavoured, made in the UK, with natural flavours and no artificial colours, and come in a bottle of 150 gummies. They are labelled 1000iu. Check the label for how many gummies make up a serving and for the diet information.
You can pair them with iron and vitamin C in The Energy Ritual, or browse our energy range.
Frequently Asked Questions
When should I start taking vitamin D in the UK?
NHS guidance suggests many people consider a daily supplement during autumn and winter, roughly October to early spring, and that some people take it all year. Check the current NHS advice for your situation.
Can I get enough vitamin D from food alone?
It is difficult. Food contributes some, but sunlight is the main source for most people, which is why autumn and winter matter.
Is 1000iu the same as 25 micrograms?
Yes. One microgram is 40 IU, so 1,000 IU is 25 micrograms.
Can I take vitamin D with iron or other supplements?
Often yes, but check that you are not exceeding the daily intake of any nutrient across everything you take. If you are unsure, ask a pharmacist.
Should I take vitamin D in summer?
Many people make enough from sunlight in spring and summer. People in the groups above may need it all year, so check NHS guidance.
Food supplements should not replace a varied, balanced diet and a healthy lifestyle. Do not exceed the recommended daily intake. Keep out of reach of children. If you are pregnant, breastfeeding, taking medication or have a medical condition, speak to your doctor before use.
