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Vitamin D Deficiency

Written by Ada’s Medical Knowledge Team

Updated on

What is vitamin D deficiency?

Vitamin D deficiency is also known as hypovitaminosis D. It is the most common nutritional deficiency worldwide, 1 affecting people of all age groups. 2

Vitamin D is one of the most important vitamins ‒ essential compounds on which the body’s cells rely for normal development. Nearly every cell in the body has a receptor for vitamin D. 3

Vitamin D levels in the body can be maintained in two ways:

  1. The body can, itself, make vitamin D from its resources of cholesterol. To do this, it needs access to sunlight.
  2. Vitamin D can be found in certain foods, such as fatty fish. (However, it is rare for a person to gain all the vitamin D that their body needs from food alone.)

Some of the most important functions of vitamin D include:

  • Maintenance of normal calcium and phosphate levels
  • Promotion of calcium absorption (essential for healthy bones and teeth)
  • Growth of cells and bones
  • Reduction of inflammation, such as can be caused by infection or injury

When a person has vitamin D deficiency, the body's cells become less efficient at carrying out processes such as growth and regeneration.

Vitamin D deficiency symptoms

If the body does not contain sufficient vitamin D, this can give rise to a variety of health complications. Symptoms arising from vitamin D deficiency include fatigue, depressed mood and bone and muscle pain.

Vitamin D is particularly instrumental in maintaining healthy bones. The development or worsening of skeletal disorders ‒ such as osteoporosis in adults and rickets in children ‒ are therefore often linked to vitamin D deficiency.

Read more about Osteoporosis »

Read more about Rickets »

The most common signs that a person may be affected by vitamin D deficiency are: 4 5

  • Bone pain, sometimes also felt as joint pain
  • Fatigue
  • Muscle pain
  • Hair loss
  • Being affected by frequent bacterial and viral infections
  • Mood changes such as a depressed mood
  • Wounds and injuries taking longer to heal
  • Weaker and/or easily breaking bones

If you are experiencing vitamin D deficiency symptoms, use the Ada app to carry out a symptom assessment.

Causes of vitamin D deficiency

The daily intake of vitamin D a person needs in order for their body to function optimally depends on factors such as age, weight, skin color, and their overall health. People whose bodies require a greater intake of vitamin D are at greater risk of experiencing vitamin D deficiency.

Being an infant or an elderly person, being obese, having darker skin and/or experiencing a health condition which compromises one’s ability to absorb vitamins properly (such as Coeliac disease or inflammatory bowel diseases) are all factors which may increase the daily quantity of vitamin D an individual requires.

Factors which increase the likelihood of being affected by vitamin D deficiency include:

  • Living in countries where there is little sun all year round
  • Having darker skin (the more pigmented a person’s skin is, the better it is able to produce melanin, which absorbs UVB radiation and reduces the synthesis of vitamin D) 6
  • Wearing high-factor sunscreen
  • Spending the majority of one’s time indoors
  • Malabsorption as a result of conditions such as Coeliac disease which impede the normal uptake of nutrients
  • Avoiding foods which provide a source of vitamin D such as fatty fish and dairy products
  • Being obese
  • Being elderly

The main source of vitamin D is exposure to solar UVB radiation (from sunlight). 4 When the body is exposed to sunlight, it can manufacture vitamin D from cholesterol, a fatty substance synthesized by the liver and found in some foods. Anything that reduces a person’s access to solar UVB radiation will compromise the body’s ability to manufacture sufficient levels of vitamin D, ref4 therefore eventually causing vitamin D deficiency.

Lacking vitamin D in one’s diet

Vitamin D deficiency can be caused by failing to gain sufficient amounts of vitamin D from one's diet, leading to insufficient levels in the body overall.

The recommended daily intake of vitamin D is: 7

  • 400 IU (international units) for children under one year
  • 600 IU for children, teens and adults up to age 70
  • 800 IU for pregnant people and adults over the age of 71

To increase a person’s chances of meeting the vitamin D target for their age group, healthcare professionals advise everybody to ensure that their diet contains sources of vitamin D – which can be found in certain foods, especially in fatty fish, such as salmon or tuna, and certain dairy products, like milk and cheese.

However, most foods that contain vitamin D do not contain sufficient quantities to meet a person’s daily required intake. For this reason, many traditionally consumed sources of vitamin D (for example, formulated milk for infants, orange juice and soy milk) are fortified with vitamin D.

Failing to eat regular or sufficient quantities of vitamin-D-containing food (for example, because of following a vegan diet) increases the likelihood of developing vitamin D deficiency. Even with a vitamin-D-rich diet, it is not usually possible for a person to maintain sufficient levels of vitamin D in their body from food alone. For this reason, vitamin D deficiency is a very common problem worldwide.

Failing to source additional vitamin D from sunlight

For some people, particularly those who ensure that their food contains vitamin D, exposure to sunlight will be sufficient for them to synthesize the rest of their recommended daily amount of vitamin D.

Many people – particularly those living far from the equator or whose lifestyles involve staying indoors and/or wearing clothes which cover most of the skin – may need to take supplements of vitamin D to meet their required daily amount. If they do not do so, this can cause vitamin D deficiency.


If vitamin D deficiency is suspected, it is important to visit a doctor in order to confirm the diagnosis, so that one can begin treatment as soon as possible and redress any problems incurred as a result of the deficiency.

It is not standard medical practice to screen symptomless people for vitamin D deficiency. Therefore, it is common for people to be unaware that they are vitamin D deficient, or that they need to take supplements, until they begin to experience health problems related to their vitamin D deficiency, such as hair loss, bone and/or muscle pain, fatigue or depression.

To confirm a suspected diagnosis of vitamin D deficiency, one’s doctor will perform a blood test (called 25-hydroxy vitamin D test) , measuring the serum 25(OH)D levels in the blood. This will determine whether a person has sufficient or insufficient levels of vitamin D.

Read more about Blood Test Results »

If an individual is suspected of having had long-term vitamin d deficiency, doctors will look for physical characteristics which are indicators of a long-term vitamin D deficiency.

Physical signs that a person may be affected by long-term vitamin D deficiency include: 8

  • Widening of the ends of the bones
  • Skeletal deformities including bow legs and expanded rib-cage
  • Slow tooth development and/or early dental caries

In diagnosing vitamin D deficiency, a healthcare professional will also assess a person’s medical history, diet and lifestyle to ascertain whether they have a history of health problems which could be related to vitamin D deficiency, like chronic liver or chronic kidney disease, and how likely they are to access sufficient sources of vitamin D on a day-to-day basis.

Vitamin D deficiency treatment

People diagnosed with vitamin D deficiency must begin treatment as soon as possible to redress the health complications which may be caused by the condition. Treatment for vitamin D deficiency normally involves supplementing a person’s nutritional intake in order to ensure that they receive the quantity of vitamin D that they need for their cells to function healthily.

The correct course of vitamin D supplementation will be decided in relation to the age of the individual, their medical history and any health conditions they may be experiencing.

Supplementation methods to treat vitamin D deficiency may include: 9

  • Oral vitamin D3 (cholecalciferol) in the form of a liquid, capsules or tablets
  • Oral calcium and vitamin D combined supplements (usually in the form of tablets)
  • Intramuscular vitamin D replacement therapy (a course of injections)

Once a plan to restore a person’s vitamin D levels to a healthy score has been devised, the doctor will consider whether any additional treatments are necessary in order to manage and/or cure any additional conditions which may have arisen as a result of the vitamin D deficiency.


In order to prevent vitamin D deficiency, doctors recommend getting as much access to sunlight as possible (with adequate precautions to prevent sunburn) and ensuring that one maintains a balanced diet which includes regular intake of sources of vitamin D.

Foods which contain or are commonly fortified with vitamin D include:

  • Oily fish. Trout, salmon, herring, sardines, pilchards, kippers, tuna.
  • Cod liver oil. This contains a large amount of vitamin D and should not be taken in conjunction with supplements containing vitamin D.
  • Fortified dairy products. Dairy-based spreads and cheese can be fortified with vitamin D. Check the nutritional information on the packet to ascertain the vitamin D content of individual products. Infant formula is generally fortified with vitamin D.
  • Fortified soy products. Soy-based products such as soy milk and soy yoghurt can be fortified with vitamin D. Check the nutritional information on the packet to ascertain the vitamin D content of individual products.
  • Natural animal products. Raw milk, meat and egg yolk are sources of vitamin D.

Good to know: It is important to note that the vitamin D content of animal products will vary according to the season. Animal products contain more vitamin D during the spring and summer months because the livestock – and the plant material they feed on – is exposed to more sunlight and thus has greater potential to synthesize vitamin D.

Vitamin D supplements

A recent evaluation of the treatment and prevention of vitamin D deficiency, undertaken on behalf of the Endocrine Society, found that most people do not achieve a sufficient intake of vitamin D from their diet and access to sunlight alone. It is therefore recommended that most people use vitamin D supplements as a means of ensuring that they reach their recommended daily intake, so as to prevent vitamin D deficiency. 10

The recommended daily intake of vitamin D supplement for each age group is: 7

  • 400 IU (international units) for children under one year
  • 600 IU for children, teens and adults up to age 70
  • 800 IU for pregnant people and adults over age 71

Individuals should consult their doctor to establish the dosage that is appropriate for them.

People may need more potent supplements of vitamin D in order to reach their required intake if they:

  • Live in countries far from the equator, for example, in Canada or middle or northern European countries which have little daylight in the winter months
  • Have a lifestyle which involves spending the majority of their time indoors
  • Usually wear clothing which covers the majority of their skin

In order to prevent hypervitaminosis D (vitamin D toxicity) which can occur if a person’s vitamin D levels are too high, it is also advisable to consult a healthcare professional before starting vitamin D supplements in order to ensure that one is not at risk of consuming too much vitamin D.

Vitamin D and UVB radiation protection: a warning

it is important to note that one should never become sunburnt in one’s efforts to spend time outdoors for the purpose of increasing one’s levels of vitamin D. Going without adequate sun protection carries significant health risks. For example, it increases the likelihood of developing severe forms of skin cancer such as melanoma.

Becoming sunburnt as a result of spending time in the sun is never recommended. One should ensure that one always takes care to wear appropriate sun protection for one’s skin type, as well as following the general recommendations, such as wearing high-factor sunscreen and a wide-brimmed hat. 11

Complications of vitamin D deficiency

It is important to consult a healthcare professional if one suspects vitamin D deficiency, because the condition increases the likelihood of developing certain problems. The most commonly experienced problems related to vitamin D deficiency are skeletal disorders; diseases related to the growth and strength of one’s bones.

In children, vitamin D deficiency can cause rickets, a condition involving the weakening and softening of the bones. In adults, the equivalent to rickets is known as osteomalacia (soft bones).

Being deficient in vitamin D can also render the body less robust and heighten the likelihood of accidents occurring:

  • Vitamin D deficiency increases the likelihood of breaking a bone in people of any age
  • Elderly people with hypovitaminosis D are more likely to fall, trip or stumble

Health complications which are associated with vitamin D deficiency include: 12

Complications of vitamin D deficiency in children

Rickets, a condition involving the softening of the bones, so that the skeleton develops deformities is a very common condition related to vitamin D deficiency and affects children worldwide. 24

In children, vitamin D deficiency primarily causes skeletal diseases because the growth of the skeleton demands certain levels of calcium, and lacking vitamin D impairs the body’s uptake of calcium. Vitamin D deficiency can therefore cause hypocalcemia (where the levels of calcium in the body are too low), which in turn can cause rickets and osteoporosis.

Children experiencing hypocalcemia as a result of vitamin D deficiency may exhibit additional symptoms and health problems, such as seizures or tetany (muscle spasms). 25 If you are concerned that your child, or a child you know, may be affected by vitamin D deficiency, get a free symptom assessment by downloading the Ada app.

Complications of vitamin D deficiency in pregnancy and infancy

Vitamin D deficiency is linked to a range of possible complications relating to pregnancy and the health of the pregnant person and the newborn.Complications which may arise for a pregnant person experiencing vitamin D deficiency include: 26

  • Gestational diabetes and less efficient metabolism of glucose
  • Bacterial vaginosis
  • Preeclampsia
  • Premature birth
  • Increased likelihood of needing a cesarean delivery

The need of the developing fetus for vitamin D increases during the second half of pregnancy, when most of the bone growth prior to birth takes place. Because a developing fetus is entirely dependent on a passive transfer of vitamin D (from the pregnant person), it is important for pregnant people to ensure that their vitamin D intake is sufficient to support the needs of the fetus in addition to their own.

In newborns, vitamin D deficiency can lead to conditions including:

  • Low birth weight
  • Rickets
  • Abnormal bone growth
  • Increased likelihood of skeletal fractures

Breastfeeding and vitamin D deficiency

it is important to ensure that a breastfeeding person maintains adequate levels of vitamin D to support the healthy growth of a newborn in the postnatal period. For most newborns, breast milk is their primary source of vitamin D. However, not all breast milk will contain sufficient levels of vitamin D to provide an infant with their recommended vitamin D intake (400 IU per day). If the amount of vitamin D present in breast milk is not sufficient, It is possible for infants to develop vitamin D deficiency, particularly if they:

  • Lack exposure to sunlight (because of staying indoors, wearing clothing which usually covers most of the skin or living far from the equator)
  • Live in weather conditions with intense cloud covering
  • Live in a highly polluted area

The American Academy of Pediatrics recommends) that a daily supplement of 400 IU should be given to all breastfeeding infants, to safeguard against vitamin D deficiency.

However, recent research indicates that if a mother takes a supplement with a sufficiently high concentration of vitamin D (around 6,400 IU), her breast milk will contain high enough levels of vitamin D to provide an infant with their recommended daily intake. 27 This removes the need to give a supplement to an infant directly.

Risks of vitamin D deficiency in the elderly

People with vitamin D deficiency are likely to experience ageing more rapidly than those with sufficient vitamin D intake.

In the elderly, a deficit of vitamin D is associated with an increased likelihood that the health problems one does experience may be difficult to treat and/or result in death more likely than without a vitamin D deficiency. Among other factors, this is because elderly people who have vitamin D deficiency are also more likely to experience cognitive impairment, compromised muscle function and are more prone to falls.

Vitamin D deficiency FAQs

Q: Does vitamin D deficiency increase the likelihood of gaining weight?
A: Vitamin D deficiency has been linked to year-round weight gain and to difficulty losing weight. People with stable and sufficient levels of vitamin D for their age and body type find it easier to maintain a healthy weight and lose weight as desired. 28 People who are putting on unwanted weight and/or struggling to lose weight despite an appropriate diet and exercise plan may be experiencing vitamin D deficiency and should consult a healthcare professional to learn if any supplements are needed.

Q: Is it possible to regrow hair in cases when hair loss is caused by vitamin D deficiency?
A: Various studies have investigated the role of vitamin D in promoting hair growth and strength and have found a link between healthy hair and sufficient levels of vitamin D. Correspondingly, hypovitaminosis D can be a contributing factor to experiencing hair loss (alopecia). However, if one experiences hair loss as a result of vitamin D deficiency, it is likely that one will need specific treatments which are designed to promote hair re-growth to replace the lost hair.

The process of replacing hair, that has been lost due to vitamin D deficiency, may involve specialised medications and/or surgery. Ensuring that one’s vitamin D intake is suitable will help to promote the effectiveness of any treatments for hair loss which a person undergoes 29 and will help to prevent further hair loss.

Q: What happens when a person takes more than their recommended daily intake of vitamin D?
A: When a person’s regular intake of vitamin D is greater than the recommended daily dose, this can result in hypervitaminosis D (vitamin D toxicity), a rare but potentially serious condition that results from having much higher than recommended levels of vitamin D in one’s body. This can stimulate the development of a range of different health complications, 30 including excessive thirst and urination, dehydration, high blood pressure, nausea and vomiting. Long-term hypervitaminosis D can result in serious problems, including cardiovascular malfunctions, calcification (hardening) of the arteries and soft tissues, and kidney problems.

Hypervitaminosis D is usually the result of taking too many supplements of vitamin D. 31 It is therefore important to consult one’s doctor before starting to use a selection of different supplementary products, so as to ensure that there is no significant overlap between the kinds of nutritional compounds that they provide. Cod liver oil, for example, has a high vitamin D content and should therefore not be taken in conjunction with any other supplementary sources of vitamin D.