How Much Vitamin D Do You Need per Day? Official Guidelines Explained

Most adults need 600 IU (15 micrograms) of vitamin D a day in the US and Canada, rising to 800 IU (20 mcg) after age 70. In the UK, the NHS advises everyone to consider a 10 mcg (400 IU) supplement each day from October to March. The safe upper limit for adults is 4,000 IU (100 mcg) a day unless a doctor recommends more. This guide explains why vitamin D matters, how much different groups need, who is most likely to be low and how to choose a supplement safely, especially now that autumn and winter sunlight are too weak in much of the northern hemisphere to make enough.

Why Do You Need Vitamin D?

Vitamin D helps the body absorb calcium and phosphate, which are needed for healthy bones, teeth and muscles. A long-term lack can lead to rickets in children and osteomalacia, a softening of the bones, in adults. Low vitamin D also contributes to osteoporosis risk in later life. Research into links with immunity, mood, heart disease and cancer has produced mixed results, and large trials have generally not found that supplements prevent those conditions in people who are not deficient.

How Much Vitamin D Do You Need per Day?

The US National Institutes of Health (NIH) Office of Dietary Supplements gives these Recommended Dietary Allowances, which Health Canada also uses:

• Babies up to 12 months: 400 IU (10 mcg).
• Ages 1–70: 600 IU (15 mcg).
• Ages 71 and over: 800 IU (20 mcg).
• Pregnancy and breastfeeding: 600 IU (15 mcg).

In the UK, the NHS advises that adults and children over four should consider taking 10 mcg (400 IU) a day in autumn and winter. People who get little sun all year round should consider taking it every day of the year. Babies who are breastfed should have a daily supplement of 8.5 to 10 mcg, while babies on more than 500 ml of formula a day usually don’t need one because formula is fortified.

The different numbers reflect different assumptions about sunlight and what counts as an adequate blood level. They are not contradictory: both are designed to keep most people’s levels high enough for bone health.

What Is the Difference Between IU and Micrograms?

Vitamin D is measured in two units. 1 microgram (mcg) equals 40 international units (IU), so 10 mcg is 400 IU, 15 mcg is 600 IU and 25 mcg is 1,000 IU. US labels usually show both, while UK labels often show only micrograms.

Can You Get Enough Vitamin D From the Sun?

Your skin makes vitamin D when exposed to ultraviolet B (UVB) light. In summer, short periods outdoors with forearms and hands uncovered can be enough for many people. But north of about 35 to 40 degrees latitude, which includes most of the northern US, Canada, the UK and Europe, the winter sun is too low for the skin to make much vitamin D from roughly October to March.

How much you make also depends on skin tone, age, clothing, sunscreen, cloud cover and air pollution. Darker skin needs more sun exposure to produce the same amount, and the skin becomes less efficient with age. Because of the risk of skin cancer, health bodies do not recommend deliberately getting sunburnt to raise vitamin D.

Which Foods Contain Vitamin D?

Few foods naturally contain much vitamin D. The best sources are:

• Oily fish such as salmon, trout, sardines, herring and mackerel.
• Cod liver oil, which is very high in vitamin D and also contains vitamin A, so don’t combine it with other high-dose vitamin A supplements.
• Egg yolks.
• Red meat and liver, in small amounts.
• Mushrooms exposed to UV light.
• Fortified foods such as some breakfast cereals, fat spreads and plant milks. In the US and Canada, cow’s milk is fortified, and Canada also fortifies margarine.

Even with a good diet, it is hard to reach 600 IU a day from food alone, which is why supplements are often advised in winter.

Who Is Most at Risk of Low Vitamin D?

• People who are rarely outdoors, including those who are housebound or live in care homes.
• People who usually cover most of their skin when outside.
• People with dark skin, such as those of African, African-Caribbean or South Asian heritage living in northern countries.
• Older adults.
• People with obesity, because vitamin D is stored in body fat.
• People with conditions that affect fat absorption, such as Crohn’s disease, coeliac disease or after weight-loss surgery.
• Breastfed babies who don’t receive a supplement.

How Do You Know If You Are Deficient?

Mild deficiency often causes no symptoms. More severe deficiency can cause bone pain, muscle weakness and aches. The only way to know your level is a blood test for 25-hydroxyvitamin D. According to the NIH, a level of 50 nmol/L (20 ng/mL) or more is adequate for bone health in most people, while levels above 125 nmol/L (50 ng/mL) may be linked to harm. Routine testing isn’t recommended for healthy people with no symptoms, so ask your doctor if you think you may be at risk.

Can You Take Too Much Vitamin D?

Yes. Taking too much over a long time can cause high calcium levels in the blood, which can lead to nausea, vomiting, confusion, heart rhythm problems and kidney damage. The NIH sets the upper limit for adults and children aged 9 and over at 4,000 IU (100 mcg) a day, with lower limits for younger children and babies. The NHS gives the same 100 mcg limit for adults.

You can’t overdose on vitamin D from sunlight, because the body limits how much it makes. Problems almost always come from very high-dose supplements, sometimes combined with multivitamins or fortified products. Check all the labels of what you take.

What Did the Endocrine Society Recommend in 2024?

In 2024, the US Endocrine Society published guidelines recommending that healthy adults under 75 should generally not take vitamin D above the RDA or have routine blood tests. It suggested people may benefit from supplements above the RDA in a few groups: children and teenagers, adults aged 75 and over, people who are pregnant, and people with prediabetes. Most other adults are covered by the standard recommendations.

How Should You Choose a Vitamin D Supplement?

• Choose the right dose. For most adults, 400–1,000 IU (10–25 mcg) a day is a sensible range. Take higher doses only on medical advice.
• D3 or D2? Both work. D3 (cholecalciferol) may raise blood levels slightly more effectively; D2 (ergocalciferol) and some D3 sources are vegan.
• Take it with food. Vitamin D is fat-soluble, so it is absorbed best with a meal that contains some fat.
• Check other products. Multivitamins, calcium supplements and fortified drinks may already contain vitamin D.
• Look for quality marks. In the US, USP or NSF certification shows the product has been independently tested.
• Ask about interactions. Some medicines, including certain steroids, anti-seizure drugs and weight-loss drugs, affect vitamin D levels.

Balanced nutrition matters just as much. Our guide to how much protein you need per day covers another nutrient many people get wrong, and our intermittent fasting guide for beginners explains how to keep nutrition adequate with a shorter eating window.

What Are the Key Takeaways?

• Most adults need 600 IU (15 mcg) a day in the US and Canada, or 800 IU after 70.
• The NHS advises 10 mcg (400 IU) a day in autumn and winter for everyone over four.
• From October to March, winter sunlight in northern regions is too weak to make much vitamin D.
• The upper limit for adults is 4,000 IU (100 mcg) a day unless a doctor advises more.
• People who are rarely outdoors, have dark skin or are older are most at risk of low levels.

This article is general information and not medical advice. Speak to a doctor or pharmacist before taking supplements if you are pregnant, take medicines or have a health condition.

Featured image: Vitamin D pills, by Mx. Granger / Wikimedia Commons, released under CC0. Cropped, colour-graded and combined with MediaPavilion branding.

Sources

• NIH Office of Dietary Supplements — Vitamin D: fact sheet for consumers (accessed 25 October 2026).
• NIH Office of Dietary Supplements — Vitamin D: fact sheet for health professionals (accessed 25 October 2026).
• NHS — Vitamin D (accessed 25 October 2026).
• Endocrine Society — Endocrine Society recommends vitamin D supplementation for some groups (3 June 2024).
• Health Canada — Vitamin D and calcium: updated dietary reference intakes (accessed 25 October 2026).
• healthdirect Australia — Vitamin D (accessed 25 October 2026).