Vitamin D is essential for the bones and teeth, the immune system, brain health, and for regulating inflammation. The body produces vitamin D as a response to sun exposure.

Certain foods and supplements can also boost vitamin D intake. Despite its name, vitamin D is not a vitamin but a hormone or prohormone.

In this article, we look at the benefits of vitamin D, what happens to the body when people do not get enough, and how to boost vitamin D intake.

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Vitamin D plays a critical role in many bodily functions.

Healthy bones

Vitamin D promotes calcium absorption and helps maintain adequate levels of calcium and phosphorus in the blood, which is necessary for healthy bones and teeth.

Vitamin D deficiency in children can cause rickets, leading to a bowlegged appearance due to the softening of the bones, and dental problems, such as teeth not forming as they should.

Similarly, in adults, vitamin D deficiency can manifest as osteomalacia, or softening of the bones. Long-term vitamin D deficiency can also lead to osteoporosis, or low bone density, which increases the risk of fractures.

Immune function

An adequate intake of vitamin D may support good immune function and reduce the risk of autoimmune diseases.

Researchers believe there may be a link between long-term vitamin D deficiency and the development of autoimmune conditions, such as type 1 diabetes and rheumatoid arthritis, but more research is necessary to confirm the link.

Although the body can create vitamin D from sunlight, some people develop deficiencies. Factors that can influence this include:

  • Lack of sun exposure: People who live in northern climates or areas of high pollution may not get as much vitamin D as others. Those who work night shifts or do not go outside can also develop a deficiency.
  • Skin color: Pigmentation in the skin reduces the body’s ability to absorb ultraviolet B (UVB) rays. Those with darker skin tones synthesize less vitamin D from sunlight than people with lighter skin.
  • Age: The skin’s ability to synthesize vitamin D decreases with age. Older adults may also spend more time indoors.
  • Breastfeeding: Babies cannot get enough vitamin D from breast milk on its own. The American Academy of Pediatrics recommends that exclusively and partially breastfed infants receive 400 international units (IU) per day of oral vitamin D until they are weaned. After weaning, they should get at least 1,000 mL/day vitamin D-fortified formula or whole milk. Children getting less than this, or who caregivers did not breastfeed, should take 400 IU vitamin D supplements.
  • Body weight: High levels of fat in the body can limit its ability to absorb vitamin D from the skin.
  • Certain medical conditions: Vitamin D is fat soluble, meaning intake is dependent on the gut absorbing dietary fats. Conditions that limit fat absorption can decrease vitamin D intake from the diet.
  • Gastric bypass surgery: This surgery bypasses a part of the upper intestine that absorbs large amounts of vitamin D. This bypass can cause a deficiency.

The majority of people with a vitamin D deficiency do not have symptoms. However, a chronic deficiency may cause osteomalacia, which may lead to:

  • bone pain
  • joint pain
  • muscle weakness or spasms
  • problems with bone development or the teeth

Over time, weakened bones may contribute to osteoporosis and increase the risk of falls and fractures, especially in older adults.

Vitamin D deficiency can also lead to hyperparathyroidism, which is when the parathyroid glands create a hormone imbalance that raises the blood calcium levels too high.

Infancy and childhood is a period of rapid growth bone growth. Due to this, it is essential for infants to get adequate amounts of vitamin D.

Chronic vitamin D deficiency can cause rickets, which is a softening of bone tissues that can lead to the malformation of bones and joints.

Vitamin D deficiency also has links to high blood pressure in children. A 2018 study found a possible connection between low vitamin D levels and arterial wall stiffness.

The American Academy of Allergy Asthma and Immunology (AAAAI) suggests a connection between low vitamin D exposure and an increased risk of allergic sensitization.

Children who live closer to the equator, where light levels are higher, have lower rates of admission to the hospital for allergies and fewer prescriptions for epinephrine auto-injectors, or EpiPens. They are also less likely to have a peanut allergy.

A 2019 review suggests that pregnant people deficient in vitamin D may have a greater risk of developing preeclampsia and giving birth prematurely.

Researchers of a 2020 review found that there may be an association between higher vitamin D concentrations and a decreased risk. However, scientists need to carry out more clinical trials to confirm this.

Some research associates a poor vitamin D status with gestational diabetes. There may also be an association between adequate vitamin D intake reduced risk of allergy development in newborns. However, other evidence has shown high intake of vitamin D could also increase this risk.

An older 2015 study suggests that treating vitamin D deficiency may also help to eliminate asymptomatic bacterial vaginosis (BV) in females of reproductive age. BV can cause adverse effects in pregnancy.

However, other research focusing specifically on pregnant people found no links between vitamin D supplementation and the prevention of BV, so more research is necessary.

Further resources

For more in-depth resources about vitamins, minerals, and supplements, visit our dedicated hub.

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People often get their vitamin D from sunlight exposure. However, many people cannot solely rely on sunlight exposure for vitamin D production. During the winter months, when the sun is not as strong, some may need vitamin D supplements.

The following foods provide some vitamin D, too:

  • fatty fish, such as salmon, mackerel, and tuna
  • egg yolks
  • cheese
  • beef liver
  • mushrooms
  • fortified milk
  • fortified cereals and juices

People can measure vitamin D intake in micrograms (mcg) or international units (IU). One mcg of vitamin D is equal to 40 IU.

The recommended daily intakes of vitamin D are as follows:

DemographicRecommended daily intake
Infants 0-12 months400 IU (10 mcg)
Children 1-18 years600 IU (15 mcg)
Adults up to 70 years600 IU (15 mcg)
Adults over 70 years800 IU (20 mcg)
Pregnant or lactating women600 IU (15 mcg)

The upper limit that healthcare professionals recommend for vitamin D is 4,000 IU per day for adults. The National Institutes of Health (NIH) reports that vitamin D toxicity is unlikely at intakes under 10,000 IU per day, but that lower intakes could still potentially have negative effects over time.

Excessive vitamin D can lead to hypercalcemia, which may lead to fatigue, weakness, bone pain, and loss of appetite. More severe symptoms can include:

  • nausea or vomiting
  • dehydration
  • excessive thirst
  • excessive urination
  • kidney stones
  • confusion
  • apathy

In extreme cases, hypercalcemia can harden soft tissues, such as blood vessels, or lead to a coma. The condition can be life threatening and requires immediate medical attention.

If someone is taking supplements, they should choose their brand carefully, as the Food and Drug Administration (FDA) does not monitor the safety or purity of supplements the same way it does pharmaceuticals.

Below are answers to some frequently asked questions about vitamin D.

What does vitamin D do for the body?

Vitamin D supports bone strength. It may also help with blood sugar regulation and maintaining healthy blood pressure, but research on this has had mixed results.

What is the best source of vitamin D?

The most accessible source of vitamin D, for many people, is sunlight. For those who cannot get sun exposure, supplements or food sources can provide their daily requirement.

How do I raise my vitamin D level quickly?

Spending a short amount of time in the sun, with some skin exposed, can raise vitamin D levels. It is important to protect the skin and eyes from the harmful effects of UV light when outside, though.

People can also take vitamin D supplements to raise their levels. Few foods naturally contain substantial amounts of vitamin D.

What is vitamin D the main cure for?

Vitamin D is a nutrient. It does not cure diseases on its own. However, it does support many bodily functions, so getting enough may be beneficial for reducing the risk of certain conditions.

The body produces vitamin D via sun exposure. Supplements and a small number of foods also contain vitamin D. The vitamin plays an important role in maintaining the bones and teeth, and may support other bodily functions, too.

Research into the benefits of adequate vitamin D is still ongoing. A vitamin D deficiency can lead to weakened bones and osteoporosis. In excessive doses, vitamin D toxicity can cause hypercalcemia, which can be serious.