what does vitamin d does

what does vitamin d does

Vitamin D is a fat-soluble vitamin in a family of compounds that includes vitamins D1, D2, and D3.

Your body produces this vitamin naturally when it’s directly exposed to sunlight. You can also get it from certain foods and supplements to ensure adequate levels of the vitamin in your blood.

It has several important functions. Perhaps the most vital are regulating the absorption of calcium and phosphorus and facilitating normal immune system function

Getting enough D vitamin is important for the typical growth and development of bones and teeth, as well as improved resistance to certain diseases.

Here is more information about the benefits of vitamin D, plus information about downsides, how much you need, and foods with

1. Vitamin D may fight disease

In addition to its primary benefits, research suggests that this may also play a role in:

  • Reducing the risk of multiple sclerosis (MS). A 2018 review of population-based studies found that low levels of vitamin D are linked with an increased risk of MS (2Trusted Source).
  • Decreasing the chance of heart disease. Low vitamin levels have been linked to increased risk of heart diseases such as hypertension, heart failure, and stroke. But it’s unclear whether its deficiency contributes to heart disease or simply indicates poor health when you have a chronic condition (3Trusted Source).
  • Reducing the likelihood of severe illnesses. Although studies are mixed, vitamin D may make severe flu and COVID-19 infections less likely. A recent review found that low levels contribute to acute respiratory distress syndrome (4Trusted Source5Trusted Source).
  • Supporting immune health. People who do not have adequate levels might be at increased risk of infections and autoimmune diseases, such as rheumatoid arthritis, type 1 diabetes, and inflammatory bowel disease

2. Vitamin D may regulate mood and reduce depression

Research has shown that vitamin D might play an important role in regulating mood and decreasing the risk of depression.

A review of 7,534 people found that those experiencing negative emotions who received supplements noticed an improvement in symptoms. Its supplementation may help people with depression who also have a deficiency urce).

Another study identified low vitamin levels as a risk factor for more severe fibromyalgia symptoms, anxiety, and depression (8Trusted Source).

3. It might support weight loss

People with higher body weights have a greater chance of low vitamin D levels

In one study, people with obesity who received vitamin D supplements in addition to following a weight loss diet plan lost more weight and fat mass than the members of the placebo group, who only followed the diet plan

In an older study, people taking daily calcium and vitamin D supplements lost more weight than subjects taking a placebo supplement. The researchers suggest that the extra calcium and vitamin D may have had an appetite-suppressing effect (10).

The current research doesn’t support the idea that would cause weight loss, but there appears to be a relationship between weight.

Looking for a vitamin D supplement?

We did the research for you. See Healthline’s picks for the 13 best vitamin supplements.

Vitamin D deficiency

Several factors can affect your ability to get adequate vitamin D from sunlight alone.

You may be less likely to absorb enough vitamin D from the sun if you (1Trusted Source):

  • live in an area with high pollution
  • use sunscreen
  • spend most of your time indoors
  • live in a big city where buildings block sunlight
  • have darker skin (The higher the levels of melanin, the less vitamin D your skin can absorb.)

These factors can increase your risk of deficiency. That’s why it’s important to get some of your vit from non-sunlight sources.

What are the symptoms of vitamin D deficiency?

The symptoms of a vitamin D deficiency in adults may include (1Trusted Source):

  • tiredness, aches, and pains
  • severe bone or muscle pain or weakness
  • stress fractures, especially in your legs, pelvis, and hips

A healthcare professional can diagnose its deficiency by performing a simple blood test. If you have a deficiency, your doctor may order X-rays to check the strength of your bones.

If you receive a diagnosis of vitamin deficiency, a healthcare professional will likely recommend that you take these supplements. If you have a severe deficiency, they may instead recommend high dose vitamin D tablets or liquids.

You should also make sure to get vitamin D through sunlight and the foods you eat.

Risks of getting too much vitamin D

If you take excessive amounts of vitamin D supplements, you may get too much of it. However, this is unlikely to happen through diet or sun exposure because your body regulates the amount of vitamin D produced through sun exposure.

Vitamin D toxicity can lead to an increase in your blood calcium levels. This can result in a variety of health issues, such as (11Trusted Source):

  • nausea
  • apathy
  • vomiting
  • abdominal pain
  • dehydration
  • confusion
  • increased thirst

Some food sources of vitamin D

Some foods contain vitamin D naturally, and others are fortified with it. You can find vitamin D in the following foods (1Trusted Source):

  • salmon
  • sardines
  • herring
  • canned tuna
  • cod liver oil
  • beef liver
  • egg yolk
  • shrimp
  • regular mushrooms and those treated with ultraviolet light
  • milk (fortified)
  • certain cereals and oatmeals (fortified)
  • yogurt (fortified)
  • orange juice (fortified)

It can be hard to get enough vitamin D each day through sun exposure and food alone, so taking vitamin D supplements could help.

How much do you need?

There has been some debate over the amount of vitamin D required for optimal functioning. Recent studies indicate that we need more vitamin D than previously thought.

Some of the main controversies surrounding vitamin D are (11Trusted Source12Trusted Source):

  • standardization of methods for measuring vitamin D levels
  • the difference between free and total vitamin D testing
  • defining low vitamin D status (insufficiency versus deficiency)
  • screening versus treatment
  • vitamin D threshold for the general population relative to a particular condition (such as pregnancy or breastfeeding) and health issues (such as kidney failure or osteoporosis)

Blood serum levels considered adequate range from 50–100 nanomoles per liter (nmol/L). Depending on your blood level, you may need more vitamin D.

The Recommended Dietary Allowances for vitamin D are as follows (1Trusted Source):

  • infants (0–12 months): 10 mcg (400 IU)
  • children and teens: 15 mcg (600 IU)
  • adults ages 18–70: 15 mcg (600 IU)
  • adults over age 70: 20 mcg (800 IU)
  • pregnant or breastfeeding women: 15 mcg (600 IU)

The bottom line

Vitamin D has many potential benefits. It may reduce the risk of certain diseases, help improve mood and reduce depression symptoms and help with weight management.

It’s hard to get enough vitamin D through your diet alone, so you may want to ask a healthcare professional for a blood test and consider taking a vitamin D supplement.


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 roleTrusted Source 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, deficiency manifests as osteomalaciaTrusted Source, or softening of the bones. Osteomalacia results in poor bone density and muscular weakness.

A vitamin 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

2018 review trusted Source of existing research suggested that some studies had found that had a protective effect against the influenza virus.

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

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

3. Healthy infants

Its deficiency has links to high blood pressure in children. One 2018 study found a possible connection between low vitamin 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 the 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 intakeTrusted Source. Eggs are a common early source of vitamin. 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 may enhance the anti-inflammatory effects of glucocorticoids. This benefit makes it potentially useful as a supportive therapy trusted Source for people with steroid-resistant asthma.

4. Healthy pregnancy

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

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

It is also important to note that in a 2013 study trusted Source, researchers associated high 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 a deficiency can occur for many reasons.


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 that

Sunscreen: A sunscreen with a sun protection factor (SPF) of 30 can reduce the body’s ability to synthesize the vitamin by 95% or moreTrusted Source. Covering the skin with clothing can inhibit 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 from food sources whenever possible.

Breastfeeding: Infants who exclusively breastfeed need a 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 unitsTrusted Source (IU) per day of oral vitamin D.

Supplement drops for babies are available online.

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

Read more on the deficiency.


Symptoms of this vitamin deficiency may include:

If its deficiency continues for long periods, it may result in complicationsTrusted Source, such as:

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

Sources of vitamin D

Getting sufficient sunlight is the best way to help the body produce enough vitamin. Plentiful food sources of vitamins 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 from the sun.


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

The recommended daily intakesTrusted Source 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 vitamins. However, vitamin breaks down quite quickly, meaning that stores can run low, especially in winter.

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