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A 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 several reasons, including maintaining healthy bones and teeth. It may also protect against a range of diseases and conditions, such as type 1 diabetes.

Despite its name, vitamin D is not a vitamin, but a prohormone, or precursor of a hormone.

Vitamins are nutrients that the body cannot create, and so a person must consume them in the diet. However, the body can produce vitamin D.

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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During sun exposure, a person's body produces vitamin D.

Vitamin D has multiple roles in the body. It assists in:

  • promoting healthy bones and teeth
  • supporting immune, brain, and nervous system health
  • regulating insulin levels and supporting diabetes management
  • supporting lung function and cardiovascular health
  • influencing the expression of genes involved in cancer development

Read on to find out about these roles in more detail:

1. Healthy bones

Vitamin D plays a significant role in the regulation of calcium and maintenance of phosphorus levels in the blood. These factors are vital for maintaining healthy bones.

People need vitamin D to allow the intestines to stimulate and absorb calcium and reclaim calcium that the kidneys would otherwise excrete.

Vitamin D deficiency in children can cause rickets, which leads to a severely bowlegged appearance due to the softening of the bones.

Similarly, in adults, vitamin D deficiency manifests as osteomalacia, or softening of the bones. Osteomalacia results in poor bone density and muscular weakness.

A vitamin D deficiency can also present as osteoporosis, for which over 53 million people in the United States either seek treatment or face an increased risk.

2. Reduced risk of flu

A 2018 review of existing research suggested that some studies had found that vitamin D had a protective effect against the influenza virus.

However, the authors also looked at other studies where vitamin D did not have this effect on flu and flu risk.

Further research is, therefore, necessary to confirm the protective effect of vitamin D on the flu.

3. Healthy infants

Vitamin D deficiency has links to high blood pressure in children. One 2018 study found a possible connection between low vitamin D levels and stiffness in the arterial walls of children.

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

An example of this is children who live closer to the equator and have lower rates of admission to hospital for allergies plus fewer prescriptions of epinephrine autoinjectors. They are also less likely to have a peanut allergy.

The AAAAI also highlight an Australian study of egg intake. Eggs are a common early source of vitamin D. The children who started eating eggs after 6 months were more likely to develop food allergies than children who started between 4–6 months of age.

Furthermore, vitamin D may enhance the anti-inflammatory effects of glucocorticoids. This benefit makes it potentially useful as a supportive therapy for people with steroid resistant asthma.

4. Healthy pregnancy

A 2019 review suggests that pregnant women who are deficient in vitamin D may have a greater risk of developing preeclampsia and giving birth preterm.

Doctors also associate poor vitamin D status with gestational diabetes and bacterial vaginosis in pregnant women.

It is also important to note that in a 2013 study, researchers associated high vitamin D levels during pregnancy with an increased risk of food allergy in the child during the first 2 years of life.

Although the body can create vitamin D, a deficiency can occur for many reasons.

Causes

Skin type: Darker skin, for example, and sunscreen, reduce the body's ability to absorb the ultraviolet radiation B (UVB) rays from the sun. Absorbing sunlight is essential for the skin to produce vitamin D.

Sunscreen: A sunscreen with a sun protection factor (SPF) of 30 can reduce the body's ability to synthesize the vitamin by 95% or more. Covering the skin with clothing can inhibit vitamin D production also.

Geographical location: 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: Infants who exclusively breastfeed need a vitamin D supplement, especially if they have dark skin or have minimal sun exposure. The American Academy of Pediatrics recommend that all breastfed infants receive 400 international units (IU) per day of oral vitamin D.

Supplement drops for babies are available online.

Although people can take vitamin D supplements, it is best to obtain any vitamins or minerals through natural sources wherever possible.

Read more on vitamin D deficiency.

Symptoms

Symptoms of vitamin D deficiency may include:

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, especially breast, prostate, and colon.

Getting sufficient sunlight is the best way to help the body produce enough vitamin D. Plentiful food sources of vitamin D include:

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

Here, learn how to get more vitamin D from the sun.

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

The recommended daily intakes of vitamin D are as follows:

  • Infants 0–12 months: 400 IU (10 mcg).
  • Children 1–18 years: 600 IU (15 mcg).
  • Adults up to 70 years: 600 IU (15 mcg).
  • Adults over 70 years: 800 IU (20 mcg).
  • Pregnant or lactating women: 600 IU (15 mcg).

Sensible sun exposure on bare skin for 5–10 minutes, 2–3 times per week, allows most people to produce sufficient vitamin D. However, vitamin D breaks down quite quickly, meaning that stores can run low, especially in winter.

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) say that vitamin D toxicity is unlikely at intakes under 10,000 IU per day.

Excessive consumption of vitamin D can lead to over calcification of bones and the hardening of blood vessels, kidney, lung, and heart tissues.

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

Excess vitamin D usually occurs from taking too many supplements. It is best to get vitamin D from natural sources.

If someone is taking supplements, they should choose their brand carefully, as the FDA do not monitor the safety or purity of supplements.

There is a selection of vitamin D supplements available for purchase online.

It is the total diet and eating pattern that is most important in disease prevention and good health. It is better to eat a diet with a variety of nutrients than to concentrate on one nutrient as the key to good health.

Q:

Is sunlight exposure worth the skin cancer risk to make sure people get enough vitamin D?

A:

It does seem like 10–15 minutes of sun exposure a few times a week is harmless, but that exposure can have consequences over your lifetime.

As little as 60 seconds of UVA exposure to the sun can increase your risk for melanoma. You are likely to get enough vitamin D through food, and increasing your intake of vitamin D through sun exposure is not worth the added risk.

If you are not getting enough, then seek out supplements. Experts also recommend that if you will be going outside, you apply sunscreen every 2 hours with a good, broad spectrum sunscreen of SPF 15 or higher. A useful resource for this type of information is skincancer.org.

Debra Sullivan, PhD, MSN, RN, CNE, COI Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.