Vitamin D
Vitamin D[1] is a hormone.[2] It is a steroid that is made in the body under the right conditions. It is stored in the fat (lipid) in the body. The body needs sunlight, which acts on the lower layers of the skin to make vitamin D. If the body does not make enough then it can be found from food sources in tiny amounts.[1][3] During seasons where there is less sunlight (in autumn and winter), dietary vitamin D is needed to make up for the lack of sunlight.[3] Because food sources offer tiny amounts of vitamin D, some people (including pregnant and breastfeeding women) need to take supplements during seasons where it is sunny less.[3]
| Vitamin D | |
|---|---|
| Drug class | |
 Vitamin (D3) in its inactive form (cholecalciferol) | |
| Class identifiers | |
| Synonyms | Calciferols |
| Use | Rickets, osteoporosis, osteomalacia, vitamin D deficiency |
| ATC code | A11CC |
| Biological target | vitamin D receptor |
| Clinical data | |
| Drugs.com | MedFacts Natural Products |
| External links | |
| MeSH | D014807 |
| Legal status | |
During times which there is enough sunlight, people can usually get enough vitamin D from diet alone.[3] Vitamin D is a fat-soluble vitamin. This makes it so that any portion not used immediately can be stored in fat tissue for future use. This is useful during sunny months. Many countries add vitamin D to certain foods like milk.[4] Supplements[1] can be easily found in most developed countries and this is another source of vitamin D.[3][5] Usually, human beings are able to get enough vitamin D from diet alone.[3]
Use
In the body
The processing and use (bioavailability) of vitamin D in the body may depend on the form used. Two example forms of vitamin D are dietary (from diet) and from dietary supplements. The sun (UV rays) helps the body make an inactive form of vitamin D3 (cholecalciferol) from cholesterol. When there is less sunlight, less D3 is made in the body. The inactive vitamin D3 is processed by the liver into its active (useful) form.
Vitamin D synthesis by the liver from cholesterol into its active form calcitriol (25-hydroxyvitamin):
- 7-dehydrocholesterol by sun (UV) rays → cholecalciferol in liver → calcidiol
The processed vitamin D is now 25-hydroxyvitamin D3 a (called calcitriol).
Types
In total, there are 5 different forms, D1 to D5. The most common ones are D2 and D3. In the body, D3 is more potent. As a supplement, D2 and D3 work the same as one-another.[5]
D3 (also called cholecalciferol)[6][7] is the kind produced by the body. It is also found naturally in marine oils and in lanolin (oil from sheep's wool), the most common source for supplements.
D2 (also called ergocalciferol)[7][8] is produced by fungi. It is similar to D3, but not exactly the same chemically. The difference between the two is that they have a double bond between C22 and C23, and a methyl group at C24 while cholecalciferol does not.[8]
Sources of vitamin D
D3 is made in the skin from cholesterol, and changed into a more active form by the liver. However, the skin will not make it unless enough ultraviolet light shines on it. As sunlight contains ultraviolet light, getting enough sun is one way of getting enough D3.
Getting enough vitamin D3
During months where there is less sunlight, supplements can be used to keep a healthy level of vitamin D. Outside of the months from April to the end of September in the UK, daily supplements are recommended by the Department of Health and Social Care and NHS.[3] The NHS recommends that babies less than 1 year old can also take vitamin D supplements if they are at risk, from 8.5mcg to 10mcg a day.[3] Babies that are fed formulae of less than 500mg a day or are breastfed can take 8.5mcg to 10mcg of vitamin D supplements per day.
Dietary sources of vitamin D
Few foods naturally contain much D3. Fish do, especially oily ones, such as salmon, sardine and mackerel. Many kinds of edible mushrooms contain some D2, like shiitake. Mushrooms grown in full sunlight tend to have more. During sunny months the body should be able to get the vitamin D it needs from sunlight alone.[3]
Supplements
Less than 25 micrograms (1000 IU) per day, or up to 100 mcg (4000 IU) per day is considered safe.[9] 10 micrograms (mcg) a day should be enough for most people living in the UK.[3] The Department of Health and Social Care recommends that people over the age of 4 take vitamin D supplements if they do not go outside a lot, wear clothes which cover up the skin when they are outdoors, or for people in care homes. A recent panel of Vitamin D researchers concluded that at least 20-25 mcg (800-1000 IU)[5] per day would help most adults.[10] Vitamin D supplements containing D2 or D3 are as effective as each other as supplements, but D3 is more potent.[5] Taking too much vitamin D (from supplements) over a long time can cause calcium buildup, making the bones weaker. This can make bones fracture easier. High amounts of vitamin D can cause problems with the heart and kidneys.[3]
During winter and autumn, people might choose to take vitamin D supplements. Because these seasons have less sunlight daily, the body might struggle to make vitamin D on its own. People at risk (such as people with darker skin and women who are pregnant or breastfeeding) should take 10 micrograms of vitamin D daily in darker months.[3] People aged 1 to 4 years old can benefit from taking 10 micrograms of vitamin D every day.
The Department of Health and Social Care recommends that babies less than 1 year old can take vitamin D supplements containing 8.5 to 10 micrograms of vitamin D if they are breastfed, or formula-fed and take less than 500ml of infant formula a day,[3] because infant formula is already fortified with vitamins and minerals.
Some people have medical conditions which makes it unsafe for them to take as much vitamin D.[3]
Dose
The amount of vitamin D needed is different for each age group. The country that someone lives in, time of year (seasons with less sunlight affect the amount of vitamin D the body gets), and being a part of an at-risk group of people increases the need for vitamin D. Melanated people need more vitamin D, because melanin can prevent the body making vitamin D naturally. Other at risk groups are pregnant or breastfeeding women. At-risk people can take 10 micrograms of vitamin D supplements year round.[3] Other people taking the same amount should not cause any harm.[3] Vitamin D3 20 mcg is equivalent to 800 IU (international units).[5] This means 1 mcg of vitamin D equals 40 IU (10 micograms = 400 IU).[3][11]
During the COVID-19 pandemic, studies thought that taking vitamin D could reduce the risk of getting COVID-19. There is not enough evidence for some health organizations to support the idea that it might.[3] Zinc supplements taken before getting a cold is sometimes though to be a prophylactic for common cold.
Overdose
Vitamin D can be toxic in large amounts. Taking too much vitamin D (usually caused by supplements) can be damaging to the body. Taking large amounts over a long period of time, it harms the bones, kidney and heart. Taking more than 100 mcg (4,000 UI) of vitamin D a day can be harmful. This applies to adults, including pregnant and breastfeeding women, and children (aged 11-17 years old). Children aged 1 to 10 years should not take more than 50 micrograms (or 2,000 UI) a day, as this amount can be harmful to them. Infants (babies under 1 years old) should not take more than 25 mcg (1,000 UI) a day. Taking too much or taking a lot over a long period of time can damage the body.
Deficiency
Many things can keep the skin from making enough D3. Winter sunlight may be too weak. Melanin, which protects skin from damage, also keeps it from making D3, which is why people with darker skin are more prone to deficiency. Older people are also prone, because aging skin makes less D3, even with enough sunlight. Clothing, glass, sunscreens and sunblocks also shield the skin from getting enough ultraviolet light to make D3. Sun cream can block some UV radiation, but it does this on purpose to prevent sunburn and cancer. During the sunny months there is usually enough daylight to get enough vitamin D from diet and sunlight naturally, and sunbathing causes the skin to make vitamin D faster. The vitamin can be stored in fat tissue, so making extra can be a source for the body if for example there is a time without the sun.
People at risk of vitamin D deficiency can get enough from supplements or fortified foods.[3][5] During the winter, the risk is higher, and people (including pregnant and breastfeeding women) can take supplements to get enough vitamin D.[3] Other people at risk of vitamin D deficiency are babies and young children (ages 1 to 4).[3] However, some infant formulae is fortified with vitamins and minerals including vitamin D.
Vitamin D Media
Children being given cod liver oil, Cambridgeshire, England, 1944
Scott's Emulsion of Pure Cod Liver Oil Trade Card
Chemical structure of cholecalciferol, aka vitamin D3.
Chemical structure of 22-Dihydroergocalciferol (vitamin D4)
Vitamin D5 or Sitocalciferol
X-ray of the legs of a two-year-old child with rickets showing bowing of the femur and low bone density
Calcium and Vitamin D3 are often combined, with claims for adult bone health. (This label predates current US Food and Drug Administration regulations on health claims.))
In the epidermal strata of the skin, vitamin D production is greatest in the stratum basale (colored red in the illustration) and stratum spinosum (colored light brown).
Vitamin D biosynthesis in animal and fungi
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Related pages
- Vitamin C (ascorbic acid) and vitamin E
- Hormones
- Rickets
References
- ↑ 1.0 1.1 1.2 World, Fitness. 7 Astonishing Effects of Taking Vitamin D Supplements, Says Science (in en). Medium (2021-06-26). Retrieved 2021-06-27.
- ↑ MeSH Browser. meshb.nlm.nih.gov. Retrieved 2026-04-01.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 Vitamins and minerals - Vitamin D (in en). nhs.uk (2017-10-23). Retrieved 2021-04-27.
- ↑ Norman, A. W.. From vitamin D to hormone D: Fundamentals of the vitamin D endocrine system essential for good health. The American Journal of Clinical Nutrition 88 (2) (2008). p. 491S–499S. doi:10.1093/ajcn/88.2.491S.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Vitamin D. drugs.com.
- ↑ MeSH Browser. meshb.nlm.nih.gov. Retrieved 2026-04-10.
- ↑ 7.0 7.1 Soto-Dávila, Manuel. Effects of Vitamin D2 (Ergocalciferol) and D3 (Cholecalciferol) on Atlantic Salmon (Salmo salar) Primary Macrophage Immune Response to Aeromonas salmonicida subsp. salmonicida Infection. Frontiers in Immunology 10 (2019). p. 3011. doi:10.3389/fimmu.2019.03011.
- ↑ 8.0 8.1 MeSH Browser. meshb.nlm.nih.gov. Retrieved 2026-04-10.
- ↑ DRIs for Calcium and Vitamin D - Institute of Medicine. Retrieved 2013-08-16.
- ↑ Dawson-Hughes, Bess. Estimates of optimal vitamin D status. Osteoporosis International 16 (7) (1 July 2005). p. 713–716. doi:10.1007/s00198-005-1867-7.
- ↑ What is Mcg in Vitamins? Guide to Vitamin Labels (in en). Nature Made®. Retrieved 2026-04-19.
Other websites
- Benefits and sources of Vitamin D Archived 2012-01-10 at the Wayback Machine
- Benefits of Vitamin D Archived 2019-04-07 at the Wayback Machine
- Factsheet on Vitamin D
- FDA takes Vitamin D drugs and feeds them to prisoners Archived 2007-03-28 at the Wayback Machine