Vitamin D3 is a form of vitamin D, the vitamin the body makes when skin is exposed to sunlight. It is also called the ‘sunshine vitamin’. Vitamin D helps the body in several ways, and the amount a person needs each day depends on age. In the United States, most people have adequate blood levels of vitamin D, according to the National Institutes of Health (NIH). But some people do not get enough, and a blood test is the only way to know your own level.
What is this vitamin and what is it for?
Vitamin D3 is made in human skin by exposure to ultraviolet B rays from the sun. It also enters the body with food. Very few foods naturally contain vitamin D. Vitamin D is primarily needed for the health of bones, joints, and muscles, as it regulates calcium and phosphate in the body. The normal level of vitamin D in children helps prevent rickets and skeletal deformity. In adults, low vitamin D can cause osteomalacia, a softening of the bones. Vitamin D helps the body absorb calcium, which keeps bones and teeth strong. It also helps muscles work and supports the immune system.
How Much Vitamin D Do I Need Each Day?
The NIH Office of Dietary Supplements publishes recommended amounts by age. The amounts below are the recommended dietary allowances (RDAs), except for babies under 1 year, where the figure is the adequate intake (AI).
| Age | Daily amount of vitamin D |
|---|---|
| Birth to 12 months | 10 micrograms (400 IU) |
| Children 1 to 13 years | 15 micrograms (600 IU) |
| Teens 14 to 18 years | 15 micrograms (600 IU) |
| Adults 19 to 70 years | 15 micrograms (600 IU) |
| Adults 71 years and older | 20 micrograms (800 IU) |
| Pregnant and breastfeeding women | 15 micrograms (600 IU) |
Do not take more than the upper limit unless your doctor advises it. For adults, the upper limit is 100 micrograms (4,000 IU) a day. For children aged 1 to 3 years it is 2,500 IU a day; for children aged 4 to 8 years it is 3,000 IU a day; and for children aged 9 to 18 years it is 4,000 IU a day. For infants up to 6 months it is 1,000 IU a day, and for infants aged 7 to 12 months it is 1,500 IU a day. The NHS in the UK advises that children from the age of 1 year and adults need 10 micrograms (400 IU) of vitamin D a day, and that everyone should consider taking a daily vitamin D supplement during the autumn and winter. A doctor can advise on the right amount for a person.
What Does Vitamin D Do?
According to the National Institutes of Health (NIH), vitamin D helps the body absorb calcium. Calcium keeps bones and teeth strong. Vitamin D also helps muscles work and supports the immune system. Without enough vitamin D, bones can become thin and weak. In children, low vitamin D can cause rickets, a condition that softens the bones. In adults, low vitamin D can cause osteomalacia, a softening of the bones.
Where Does Vitamin D Come From?
According to the NIH, the main source of vitamin D is sunlight. The skin makes vitamin D when it is exposed to ultraviolet B rays. Food sources include fatty fish such as salmon and mackerel, fish liver oils, egg yolks, and foods with added vitamin D, such as milk and breakfast cereals. Almost all of the milk in the United States is fortified with about 120 IU of vitamin D per cup. In winter, sunlight is weak in many places. People may get less vitamin D from the sun. According to the NHS, between October and early March we do not make enough vitamin D from sunlight in the UK, and government advice is that everyone should consider taking a daily vitamin D supplement during the autumn and winter.
Who Is at Risk of Low Vitamin D?
According to the NIH, some people are more likely to have low vitamin D. These include breastfed infants, because breast milk has little vitamin D; older adults, because the skin’s ability to make vitamin D falls with age; people who seldom expose their skin to sunshine; people with dark skin; people with conditions that limit fat absorption, such as Crohn’s disease, coeliac disease, or ulcerative colitis; and people with obesity or who have had gastric bypass surgery. A doctor can check vitamin D levels with a blood test. A person should not guess their level. A blood test gives the answer.
Signs of Low Vitamin D
According to the NIH, vitamin D deficiency causes rickets in children, a disease in which the bones become soft, weak, deformed, and painful. In teens and adults, vitamin D deficiency causes osteomalacia, a disorder that causes bone pain and muscle weakness. Some people have no symptoms at all. A person with these signs should talk to a doctor. The doctor may order a blood test. A blood test is the only way to know if vitamin D is low. A person should not take high-strength supplements without a doctor’s advice. The right amount depends on age, health, and blood levels.
Can You Take Too Much Vitamin D?
Yes. According to the Mayo Clinic, vitamin D toxicity is rare and usually caused by taking large doses of vitamin D supplements. It is not likely from eating food or from sun exposure. The main concern is a buildup of calcium in the blood, called hypercalcaemia. It can cause upset stomach and vomiting, weakness, and frequent urination. It can also lead to bone pain and kidney troubles such as kidney stones. According to the NIH, extremely high levels can cause kidney failure, irregular heartbeat, and even death. The Mayo Clinic advises not to take more than 4,000 IU of vitamin D a day. The NHS gives the same limit: do not take more than 100 micrograms (4,000 IU) of vitamin D a day, as it could be harmful. Children aged 1 to 10 years should not have more than 50 micrograms (2,000 IU) a day. Always follow a doctor’s advice, not a product label.
Frequently Asked Questions
How much vitamin D should I take daily?
According to the NIH, adults aged 19 to 70 need 15 micrograms (600 IU) a day, and adults aged 71 and older need 20 micrograms (800 IU) a day. Babies up to 1 year need 10 micrograms (400 IU) a day. Do not take more than 4,000 IU a day unless your doctor advises it.
What does vitamin D do?
According to the NIH, vitamin D helps the body absorb calcium. Calcium keeps bones and teeth strong. Vitamin D also helps muscles work and supports the immune system.
Where does vitamin D come from?
According to the NIH, the main source is sunlight. Food sources include fatty fish, egg yolks, and foods with added vitamin D, such as milk and breakfast cereals.
Who is at risk of low vitamin D?
According to the NIH, breastfed infants, older adults, people who seldom expose their skin to sunshine, people with dark skin, and people with conditions that limit fat absorption are more likely to have low vitamin D.
Can too much vitamin D cause harm?
Yes. According to the Mayo Clinic, too much vitamin D can cause a buildup of calcium in the blood, leading to upset stomach and vomiting, weakness, frequent urination, bone pain, and kidney stones. Do not take more than 4,000 IU a day unless your doctor advises it.
Disclaimer: This guide is for general information only. It is not medical advice and it does not replace care from a doctor. This guide gives no medical advice for readers. Talk to a doctor before you take a vitamin D supplement, and ask for a blood test if you think your level may be low.
Last Updated: 6 November 2026