Quick answer: In the UK, everyone is advised to consider 10 micrograms (400 IU) of vitamin D a day from October to March. Canada advises a daily 400 IU supplement from age 51, and vitamin D from food or a supplement every day before that. The US recommends 600 IU (15 micrograms), or 800 IU over 70. Don't go above 4,000 IU (100 micrograms) a day unless a clinician advises it.
In this guide
Who this guidance is for, and who should ask a clinician first
This guide is for adults in the US, Canada and the UK who want to know how much vitamin D the official advice says to take through the darker months. It reports public-health guidance only. It can't tell you your own dose, and it isn't a substitute for advice from a GP, family doctor, pharmacist or primary-care clinician.
Ask a clinician or pharmacist before taking vitamin D, or before going above the standard amounts, if any of these apply:
- Kidney disease. The kidneys turn vitamin D into its active form, and people whose kidneys can't do this can become deficient, according to the NIH Office of Dietary Supplements. Your kidney team will say which form and amount suits you.
- Sarcoidosis. Sarcoidosis can make the body activate too much vitamin D. SarcoidosisUK reports high blood calcium in about 1 in 10 people with the condition, and advises having calcium and vitamin D checked before starting any supplement.
- Medicines that interact. The NIH Office of Dietary Supplements lists orlistat, steroids such as prednisone, statins (with high-dose vitamin D) and thiazide diuretics, which can push blood calcium too high alongside vitamin D.
- Pregnancy, breastfeeding, babies and children, where the amounts and upper limits differ (see below).
- Symptoms such as bone pain or muscle weakness, a bone or gut condition, or past weight-loss surgery. These are reasons for a test, not guesswork — our guide to which vitamin D test you need and when it's free explains the options.
Why does vitamin D matter more in winter?
Because in northern countries your skin makes little or none from winter sunlight. The NHS says that between October and early March people in the UK don't make enough vitamin D from sunlight, and Public Health England said that in spring and summer most people get enough from the sun plus a balanced diet, but in autumn and winter must rely on food and supplements.
Health Canada lists season, time of day, cloud, sunscreen, time outdoors, age and skin pigment as factors that cut how much vitamin D the skin makes, and says these apply to many people living in Canada. Your skin also can't make vitamin D from sunlight through a window.
Vitamin D helps the body absorb calcium for bones and is needed by muscles and nerves. Long-term shortage causes rickets in children and osteomalacia (bone pain and muscle weakness) in adults. Very few foods contain much of it; oily fish, egg yolks and fortified milks, spreads and cereals are the main sources.
Micrograms or IU: reading the label
For vitamin D, 1 microgram (mcg or µg) = 40 IU. Every official table pairs them this way: 10 micrograms is 400 IU, 15 is 600, 20 is 800 and 100 is 4,000. UK labels and NHS advice use micrograms; US and Canadian labels often show both. A "1,000 IU" tablet is 25 micrograms, which is more than the UK's 10 microgram winter advice but within the adult upper limit.
How much vitamin D is too much?
For adults, the ceiling is the same in all three countries: 100 micrograms (4,000 IU) a day, counting food, drinks and supplements together. The NIH Office of Dietary Supplements and Health Canada's reference tables set it at 4,000 IU from age 9, including in pregnancy and breastfeeding. The NHS uses the same figure for adults and children aged 11 to 17.
Children's limits are lower, and the UK's are stricter than North America's. The NHS says children aged 1 to 10 should not have more than 50 micrograms (2,000 IU) a day and babies under 12 months no more than 25 micrograms (1,000 IU). US and Canadian tables allow 2,500 IU at ages 1–3 and 3,000 IU at 4–8.
Too much vitamin D over time raises blood calcium (hypercalcaemia). The NHS says this can weaken bones and damage the kidneys and heart. The US fact sheet lists nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, passing a lot of urine, thirst and kidney stones; extremely high levels can cause kidney failure and an irregular heartbeat. It is almost always caused by high-dose supplements — sunshine can't do it, because the skin limits how much it makes.
A clinician may prescribe more than the upper limit for a set period to treat a proven deficiency. That's a treatment plan with follow-up, not something to copy from a friend or a label.
How much vitamin D in winter: US, Canada and UK advice
The UK gives the most specific winter advice; Canada and the US set year-round amounts that already assume little sun.
United Kingdom
The Scientific Advisory Committee on Nutrition set a reference intake of 10 micrograms a day for everyone aged 4 and over. The NHS turns that into everyday advice:
- Everyone, including people who are pregnant or breastfeeding, should consider 10 micrograms (400 IU) a day in autumn and winter.
- All year if you're rarely outdoors, live in a care home, usually cover most of your skin outside, or (the NHS says) may need it if you have dark skin.
- Babies: breastfed babies need 8.5 to 10 micrograms a day from birth; babies having more than 500ml of formula a day don't, because formula is fortified, according to NHS Best Start in Life. Children aged 1 to 4 should have 10 micrograms a day all year.
- Pregnancy: the NHS pregnancy guidance advises 10 micrograms a day from early October to late March.
What's free: families on the NHS Healthy Start scheme can get free vitamins — tablets with vitamin D for pregnancy and breastfeeding, and drops with vitamins A, C and D for children up to their fourth birthday. Otherwise, 10 microgram supplements are sold over the counter. When an NHS vitamin D test is free is covered in our vitamin D test guide.
Canada
Health Canada's advice applies all year, which in practice covers winter:
- Ages 2 to 50: eat foods that contain vitamin D every day, or take a daily supplement of 400 IU (10 micrograms).
- Age 51 and over: take a daily 400 IU (10 microgram) supplement, as well as eating vitamin D foods, to support bone health at a stage when bone loss increases. This wording was updated in March 2026; older material says "over 50".
- Recommended daily intake: 600 IU (15 micrograms) from age 1 to 70 and 800 IU (20 micrograms) over 70, with a 4,000 IU upper limit. Health Canada notes these values assume minimal sun exposure.
- Babies: Health Canada recommends 400 IU (10 micrograms) a day for exclusively and partially breastfed babies from birth.
What's free: there's no national supplement scheme for adults; vitamin D supplements are sold over the counter.
United States
US guidance doesn't change with the season. The NIH Office of Dietary Supplements gives recommended amounts from food and supplements combined:
- Ages 1 to 70, including pregnancy and breastfeeding: 15 micrograms (600 IU) a day.
- Over 70: 20 micrograms (800 IU) a day.
- Breastfed babies: a 10 microgram (400 IU) supplement each day.
Most US milk is fortified with about 3 micrograms (120 IU) a cup, as are many plant milks and breakfast cereals, so food can supply part of this.
On testing and extra dosing, the US Preventive Services Task Force found in 2021 that there was not enough evidence to weigh the benefits and harms of screening adults without symptoms. The Endocrine Society's 2024 guideline suggests that healthy adults under 75 stick to the standard recommended amounts and don't have routine tests. It does suggest extra (empiric) vitamin D for children and teens aged 1 to 18, adults 75 and over, pregnancy and people with high-risk prediabetes — the dose for those groups is a conversation for your clinician.
What's free: there's no national supplement scheme; vitamin D is sold over the counter, alone or in multivitamins.
Compare the guidance by country
| Question | UK (NHS, SACN) | Canada (Health Canada) | US (NIH ODS, USPSTF) |
|---|---|---|---|
| Everyday advice for adults | Consider 10 mcg (400 IU) a day, October to March | Vitamin D foods daily or 400 IU (10 mcg) supplement, ages 2–50 | 600 IU (15 mcg) a day from food and supplements |
| Older adults | Same 10 mcg; all year if rarely outdoors or in a care home | 400 IU (10 mcg) supplement daily from 51 | 800 IU (20 mcg) a day over 70 |
| Upper limit, adults | 100 mcg (4,000 IU) | 4,000 IU (100 mcg) | 4,000 IU (100 mcg) |
| Breastfed babies | 8.5–10 mcg a day from birth | 400 IU (10 mcg) a day from birth | 400 IU (10 mcg) a day |
| Upper limit, children 1–10 | 50 mcg (2,000 IU) | 2,500–4,000 IU depending on age | 2,500–4,000 IU depending on age |
| When the advice applies | Autumn and winter; all year if rarely outdoors, in a care home or skin usually covered | All year | All year |
| Free supplements | Healthy Start, for eligible families | No national scheme | No national scheme |
Guidance checked 20 October 2026. Canada's 51+ wording dates from March 2026.
What to do next
- Check the "ask first" list at the top. Kidney disease, sarcoidosis, interacting medicines, pregnancy or a child to dose: speak to a pharmacist or clinician before buying anything.
- Otherwise, follow your country's advice. In the UK, that's 10 micrograms (400 IU) a day through autumn and winter; in Canada, a daily vitamin D source and a 400 IU supplement from 51; in the US, 600–800 IU a day from food and supplements together.
- Read the label in micrograms and IU, and add up everything you take — multivitamins, fish-liver oils and fortified drinks all count towards the limit. Our guide to whether you need a multivitamin covers overlap between products.
- Don't go above 4,000 IU (100 micrograms) a day unless a clinician prescribes it and follows you up.
- Eat plant-based? Vitamin D is one of several nutrients to plan for — see what to test and what to take on a vegan diet.
The nutrition finder asks about your diet, sun, symptoms and medicines, flags anything that needs a clinician, and shows the free route before any test or product.
Check my nutritionCommon questions
Should I take vitamin D every day in winter?
In the UK, yes for most people: the NHS advises everyone to consider 10 micrograms (400 IU) a day from October to March. Canada advises a daily source of vitamin D year-round, and a 400 IU supplement from 51. US guidance sets a daily intake of 600 to 800 IU from food and supplements together.
How much vitamin D is too much?
For adults and teenagers, the upper limit is 100 micrograms (4,000 IU) a day from all sources in the UK, US and Canada. Children's limits are lower. Too much over time raises blood calcium, which can cause nausea, vomiting, confusion, thirst and kidney stones. Take more only if a clinician prescribes it.
How many IU is 10 micrograms of vitamin D?
Ten micrograms is 400 IU. For vitamin D, one microgram equals 40 IU, so 15 micrograms is 600 IU, 25 micrograms is 1,000 IU and 100 micrograms is 4,000 IU. UK labels usually show micrograms (mcg or µg), while US and Canadian labels often show both units.
Do I need a vitamin D test before taking a supplement?
Usually not. The USPSTF found too little evidence to recommend screening adults without symptoms, and the Endocrine Society suggests against routine testing in healthy adults under 75. A test makes sense if you have symptoms, a bone or absorption condition, kidney disease, or take medicines that affect vitamin D.
Related guides
Sources
- NHS. Vitamin D — who should take a supplement, how much, and upper limits. Accessed 20 October 2026.
- Scientific Advisory Committee on Nutrition (SACN). Vitamin D and health report. 2016, updated December 2023.
- Public Health England. PHE publishes new advice on vitamin D. July 2016.
- NHS. Vitamins, supplements and nutrition in pregnancy. Accessed 20 October 2026.
- NHS Best Start in Life. Baby vitamins. Accessed 20 October 2026.
- NHS Healthy Start. Getting Healthy Start vitamins. Accessed 20 October 2026.
- Health Canada. Applying Canada's Dietary Guidelines: advice on vitamin and mineral supplementation. Updated March 2026.
- Health Canada. Dietary reference intakes tables: reference values for vitamins.
- Health Canada. Nutrition for healthy term infants: recommendations from birth to six months.
- NIH Office of Dietary Supplements. Vitamin D fact sheet for consumers. Updated November 2022.
- NIH Office of Dietary Supplements. Vitamin D fact sheet for health professionals.
- US Preventive Services Task Force. Vitamin D deficiency in adults: screening (I statement). April 2021.
- Endocrine Society. Vitamin D for the prevention of disease: clinical practice guideline. June 2024.
- SarcoidosisUK. Sarcoidosis and calcium and vitamin D factsheet. 2025.
General information, not medical advice — see our medical disclaimer. Written to the WhereToStart editorial policy. Next scheduled review: .