Vitamin D is sometimes called the sunshine vitamin, because your skin makes it when it is exposed to sunlight. It plays a key role in absorbing calcium and keeping your bones, teeth and muscles healthy, and it also supports the immune system. Yet it is one of the nutrients people worry about most, and one of the most confusing: how much do you need, should you take a supplement, and do you need a blood test?
This guide explains what vitamin D does, how much adults and children need, which foods contain it, how sunlight fits in (and how to balance it with skin-cancer prevention), who may be at higher risk of low levels, and how testing and supplements work.
Key takeaways
- Most adults need about 600 IU (15 micrograms) of vitamin D a day, and adults over 70 about 800 IU (20 micrograms).
- You get vitamin D from sunlight, a few foods and supplements. Very few foods contain much of it naturally.
- Season, latitude, skin color, age and sunscreen all affect how much your skin makes.
- Routine blood testing is not recommended for healthy people, but it can make sense if you are at risk or have symptoms.
- More is not better. Very high doses of supplements can cause harm, so stay within recommended limits unless a clinician advises otherwise.
What vitamin D does
Vitamin D helps your gut absorb calcium and phosphorus, the minerals that build and maintain bone. Without enough, bones can become soft or weak: in children this causes rickets, and in adults it causes osteomalacia, which can lead to bone pain and muscle weakness. Vitamin D also contributes to muscle function and to the normal workings of the immune system.
Researchers have studied vitamin D in relation to many other conditions, from heart disease to depression to cancer. Large trials of supplements in people who were not deficient have generally not shown that extra vitamin D prevents these conditions. The clearest benefit is for bone health in people who have low levels.
How much vitamin D do you need?
The U.S. National Institutes of Health Office of Dietary Supplements gives these recommended daily amounts. They are shown in international units (IU) and micrograms (mcg); 40 IU equals 1 mcg.
| Group | Recommended daily amount | Notes |
|---|---|---|
| Infants, 0 to 12 months | 400 IU (10 mcg) | Pediatric guidance often suggests a supplement for breastfed babies. Ask your pediatrician. |
| Children and adults, 1 to 70 years | 600 IU (15 mcg) | Includes pregnancy and breastfeeding. |
| Adults over 70 | 800 IU (20 mcg) | Skin makes less vitamin D with age. |
| Upper limit for adults | 4,000 IU (100 mcg) | The highest daily amount unlikely to cause harm for most people. |
Getting vitamin D from sunlight
When ultraviolet B (UVB) rays hit your skin, it converts a compound into vitamin D. This is the most natural way to get it, but how much you make depends on many factors:
- Season and latitude. At higher latitudes, the sun is too low in winter for the skin to make much vitamin D, sometimes for several months.
- Time of day. Midday sun is strongest for vitamin D production.
- Skin pigmentation. Darker skin contains more melanin, which reduces vitamin D production, so people with darker skin may need more time in the sun or more dietary vitamin D.
- Age. Older skin makes vitamin D less efficiently.
- Clothing and sunscreen. Covered skin and sunscreen reduce production, although in everyday life sunscreen users often still make enough.
- Cloud, pollution and glass. Clouds and air pollution reduce UVB, and window glass blocks it.
Balancing sunlight and skin safety
The sun is the main cause of skin cancer, so health authorities do not recommend deliberately sunbathing to boost vitamin D. A short time outdoors in the middle of the day, a few times a week, is enough for many people in sunnier seasons. Beyond that, protect your skin with shade, clothing, a hat and broad-spectrum sunscreen. Tanning beds are not a safe source of vitamin D.
Being outside also helps in other ways. Walking in daylight supports your mood and sleep. For ideas, see our guide to how much walking you really need, which includes tips for building a daily habit.
Food sources of vitamin D
Few foods contain much vitamin D naturally, so many countries add it to certain foods. The best sources include:
| Food | Serving | Vitamin D (approx.) |
|---|---|---|
| Trout, farmed, cooked | 3 ounces | About 645 IU |
| Salmon, sockeye, cooked | 3 ounces | About 570 IU |
| Mushrooms exposed to UV light | ½ cup, sliced | About 365 IU |
| Milk, fortified | 1 cup | About 120 IU |
| Orange juice, fortified | 1 cup | About 100 IU |
| Sardines, canned | 2 sardines | About 45 IU |
| Egg, whole | 1 large | About 45 IU |
Fortified breakfast cereals, yogurts and some plant-based milks also contribute. If you do not eat fish, dairy or eggs, check labels and talk to a dietitian about whether you are getting enough.
Who is at higher risk of low vitamin D?
- Older adults, whose skin makes less and who often spend more time indoors
- People with darker skin, especially at higher latitudes
- People who spend most of their time indoors, or who cover most of their skin outdoors
- People living at higher latitudes during the winter months
- People with obesity
- People with conditions that affect absorption, such as celiac disease, Crohn’s disease, or after some types of weight-loss surgery
- People with kidney or liver disease, or who take certain medicines such as some anti-seizure drugs and long-term steroids
- Exclusively breastfed infants, since breast milk contains little vitamin D
Symptoms of low vitamin D
Many people with low vitamin D have no symptoms at all. When deficiency is severe and long-lasting, it can cause bone pain, muscle weakness or cramps, and an increased risk of fractures. These symptoms are not specific, since many other conditions cause them, so tiredness or aches alone do not mean you are deficient.
Should you get tested?
Doctors measure vitamin D with a blood test called 25-hydroxyvitamin D. Many laboratories consider levels below 12 ng/mL (30 nmol/L) as deficient, and levels of about 20 ng/mL (50 nmol/L) or above as adequate for most people. Experts do not all agree on the ideal level, and numbers vary between laboratories.
Major guidelines do not recommend routine testing for healthy people with no symptoms. Testing may make sense if you have a condition or take medicine that affects vitamin D, have signs of weak bones or frequent fractures, or belong to a high-risk group. If you want a test, talk to your clinician. Do not self-diagnose from a symptom checklist.
Supplements: what to know
- Types. Vitamin D comes as D2 and D3. Both raise blood levels, and D3 is more common and often preferred.
- Take it with food. Vitamin D is fat-soluble, so it is absorbed better with a meal that contains some fat.
- Check your multivitamin. Many already contain 400 to 1,000 IU, so avoid doubling up with a separate supplement unless advised.
- Do not exceed the upper limit without medical supervision. Very high doses over time can raise blood calcium, causing nausea, weakness, kidney problems and heart rhythm changes.
- Mind interactions. Some medicines, such as certain diuretics, can interact with vitamin D or calcium. Ask a pharmacist.
- Choose reputable brands. Look for products tested by an independent organization.
A balanced diet with adequate calcium, regular weight-bearing activity and enough sleep supports bone health as well. If you are building your diet, our guide to how to sleep better explains why rest matters too.
Common vitamin D myths
Myth: You can get all the vitamin D you need from the sun year-round.
Fact: At higher latitudes, the winter sun is too weak for your skin to make much vitamin D, and many people spend little time outdoors. Food and sometimes supplements fill the gap.
Myth: Sunscreen causes vitamin D deficiency.
Fact: In laboratory conditions, sunscreen reduces vitamin D production. In everyday life, studies show sunscreen users generally maintain healthy levels, since most people do not apply it perfectly. Do not skip sunscreen to get more vitamin D.
Myth: If a little is good, a lot is better.
Fact: Vitamin D is stored in the body, so very high doses can build up to toxic levels. Stay within recommended amounts unless a clinician advises otherwise.
When to talk to a professional
- You have bone pain, muscle weakness, frequent fractures or a diagnosis of osteoporosis.
- You have a medical condition or take medicine that affects vitamin D, calcium or absorption.
- You are considering a high-dose supplement. Do not exceed the upper limit without medical advice.
- You are pregnant, breastfeeding or have an infant and want to know whether to supplement.
Frequently asked questions
How much sun do I need for vitamin D?
There is no single amount. For many light-skinned people in sunny seasons, a short time outdoors around midday a few times a week is enough. People with darker skin, older adults, and those at higher latitudes may need more or rely on food and supplements. Always balance this against skin-cancer risk and avoid sunburn.
Is vitamin D3 better than D2?
Both raise blood levels. Many studies suggest D3 raises levels more effectively, and it is the most commonly sold form. Ask your clinician if you have specific needs, such as a vegan source.
Can you get vitamin D through a window?
Not effectively. Window glass blocks most UVB rays, which are the ones that trigger vitamin D production in your skin.
Should I take vitamin D every day?
Only if you need it. If your diet and sunlight exposure provide enough, you may not need a supplement. If you do take one, a modest daily dose within the recommended range is typical.
What are signs of too much vitamin D?
Taking very high doses over time can raise calcium in the blood, which may cause nausea, vomiting, weakness, frequent urination and kidney problems. If you suspect you have taken too much, contact a healthcare professional.
Vitamin D is essential, but you do not need to obsess over it. Get some regular daylight, include fortified or naturally rich foods in your diet, consider a supplement if you are in a higher-risk group, and ask your clinician about testing if you have a medical reason.
Sources and further reading
More wellness guides
This guide is for general information only and is not medical advice. Talk to a qualified healthcare professional about your own situation before making changes to your health routine.