Vitamin D is essential for bone strength and may support the immune system and other functions. The human body produces vitamin D as a response to sun exposure. A person can also boost their vitamin D intake through certain foods or supplements.

Vitamin D is essential for maintaining healthy bones and teeth. It also plays many other important roles in the body, including regulating inflammation and immune function.

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 intestinal calcium absorption and helps maintain adequate blood levels of calcium and phosphorus, which is necessary for healthy bone mineralization.

Vitamin D deficiency in children can cause rickets, leading to a bowlegged appearance due to the softening of the bones. Similarly, in adults, vitamin D deficiency manifests as osteomalacia or a softening of the bones. Osteomalacia results in poor bone density and muscular weakness.

Long-term vitamin D deficiency can also present as osteoporosis.

Immune function

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

Researchers suggest that vitamin D plays an important role in immune function. They believe there may be a link between long-term vitamin D deficiency and the development of autoimmune conditions, such as diabetes, asthma, and rheumatoid arthritis, but more research is necessary to confirm the link.

While test-tube studies have shown vitamin D to have a positive effect on the immune response of human cells, researchers are yet to replicate these findings in controlled human trials.

Although the body can create vitamin D, some people are more likely to be at risk of a deficiency than others. Factors that can influence this include:

  • Skin color: Pigmentation in the skin reduces the body’s ability to absorb ultraviolet B (UVB) rays from the sun. Absorbing sunlight is essential for the skin to produce vitamin D.
  • Lack of sun exposure: People who live in northern latitudes or areas of high pollution, work night shifts, or are homebound should aim to consume vitamin D from food sources whenever possible.
  • Breastfeeding: The American Academy of Pediatrics recommends that all breastfed infants receive 400 international units (IU) per day of oral vitamin D.
  • Older adults: The skin’s ability to synthesize vitamin D decreases with age. Older adults may also spend more time indoors.
  • Those with conditions that limit fat absorption: 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.
  • People with obesity: High levels of body fat can limit the body’s ability to absorb vitamin D from the skin.
  • People following a gastric bypass: This surgery bypasses a part of the upper intestine that absorbs large amounts of vitamin D. This bypass can cause a deficiency.

Read more on vitamin D deficiency.

The majority of people with a vitamin D deficiency do not present with symptoms. However, a chronic deficiency may cause hypocalcemia, a calcium deficiency disease, and hyperparathyroidism, where the parathyroid glands create a hormone imbalance that raises the blood calcium levels.

These conditions can lead to secondary symptoms including:

  • bone fragility, especially in older adults
  • osteoporosis
  • bone pain
  • fatigue
  • muscle twitching
  • muscle weakness
  • myalgias, or muscle pain
  • arthralgias, or joint stiffness

If Vitamin D deficiency continues for long periods, it may result in complications, such as:

  • cardiovascular conditions
  • autoimmune problems
  • neurological diseases
  • infections
  • pregnancy complications
  • certain cancers, including breast, prostate, and colon

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 and hypertension in children. A 2018 study found a possible connection between low vitamin D levels and arterial wall stiffness in children.

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

For example, children who live closer to the equator 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 preterm.

Researchers of a 2020 review study found that there may be an association between higher vitamin D concentrations during pregnancy and a decreased risk of preeclampsia and premature birth. However, researchers need well-designed clinical trials with vitamin D supplementation in order to better define associations.

Some research associates a poor vitamin D status with gestational diabetes. Treating vitamin D deficiency may also reduce the risk of asymptomatic bacterial vaginosis in pregnant people. However, conflicting research found no links between vitamin D supplementation and the prevention of bacterial vaginosis.

There may be an association between adequate vitamin D intake during pregnancy and a reduced risk of asthma and food allergy development in the resulting newborns. However, the evidence is not definitive, and more studies are necessary.

Further resources

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

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People can often get the majority of their vitamin D intake from sunlight exposure. However, people at risk of developing vitamin D deficiency, and many other people, cannot solely rely on sunlight exposure for vitamin D production. During the winter months, when the sun is not as strong, everyone can benefit from vitamin D supplements.

The following foods are a source of vitamin D:

  • 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)

Learn how to get more vitamin D from the sun here.

The upper limit that healthcare professionals recommend for vitamin D is 4,000 IU per day for an adult. However, the National Institutes of Health (NIH) reports that vitamin D toxicity is unlikely at intakes under 10,000 IU per day.

Vitamin D toxicity is typically the result of inappropriate supplement dosing and prescription errors.

Excessive vitamin D consumption can lead to hypercalcemia, or an excessively high blood calcium level. This can lead to calcification of bones and the hardening of blood vessels, kidneys, lungs, and heart tissues.

Hypercalcemia can be life threatening and requires immediate medical attention.

The most common symptoms of excessive vitamin D include headaches and nausea. However, too much vitamin D can also lead to the following:

Excessive vitamin D usually occurs from accidental overconsumption and prescription errors.

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.

A complete diet and regular eating pattern are most important in disease prevention and good health. It is better to eat a diet with various nutrients than to concentrate on only a few nutrients.

The body produces vitamin D due to sun exposure. Many foods and supplements also contain vitamin D. The vitamin plays an important role in maintaining bones, teeth, and optimal immune function.

A vitamin D deficiency can cause calcium deficiency disease, and hyperparathyroidism, a hormone imbalance that raises the blood calcium levels.