This fact sheet is intended to help you understand what vitamin D is, why it is important and how to get your recommended daily intake of this essential nutrient.
What is Vitamin D?
Vitamin D is a hormone, but it was first identified as a nutrient found in cod liver oil and so it was called “vitamin D” (vitamin A, some of the B vitamins and vitamin C had been discovered some time before vitamin D was identified)[i]. Vitamin D is unique because is it found in some foods and our bodies can also make it when our skin is exposed to sunlight. However, this only works when the sun is high enough in the sky. In the UK, we can make vitamin D from sunlight from April until September; a good rule of thumb is, if your shadow is shorter than you are, you can make vitamin D[ii].
Why is Vitamin D important?
Bone health: It is used in the absorption of calcium and other minerals, and in the laying down of those minerals into our bones and teeth, helping to keep them healthy and strong[i]. There is also increasing evidence that having enough vitamin D can help to prevent falls. These two benefits together mean that vitamin D can help prevent bone fractures [ii].
Immunity: Vitamin D is essential to good immunity. Some research shows that we may get more coughs and colds in the winter because we cannot make vitamin D from the winter sun, which means we have lower levels of vitamin D. There is also research that suggests that low levels of vitamin D may be linked to an increased risk of developing heart disease, some cancers, and conditions such as type I diabetes and multiple sclerosis[iii].
Every cell in our bodies has specialist receptors which recognise vitamin D. This suggests that it is involved in several different functions, many of which are not yet fully understood. Continuing research shows that there are even more functions of vitamin D to be explored. For example, in muscle function and strength[iv]; heart function and health[v], the maintenance of healthy blood pressure[vi] and in mood and reducing depression[vii].
Where is it found?
Foods containing vitamin D include:
- oily fish such as salmon, sardines, pilchards, trout, herring, kippers and eel contain reasonable amounts of vitamin D
- cod liver oil contains a lot of vitamin D, but don’t take this if you are pregnant
- egg yolk, meat, offal and milk contain small amounts, but this varies during the seasons
- margarine, some breakfast cereals, infant formula milk and some yoghurts have added vitamin D
Vitamin D supplements are widely available from pharmacies, health food shops and most supermarkets. Some people who are pregnant or breastfeeding and children aged 6 months to 4 years may qualify for Healthy Start vitamins which contain vitamin D. Ask your health visitor about this. A supplement only needs to contain 10 micrograms to meet the recommendation; those with a higher content of vitamin D are unnecessary and could be harmful in the long run.
Dept of Health and Social Care recommends that everyone should take a 10 microgram (a microgram symbol looks like this µg) vitamin D supplement, throughout autumn and winter[i], although it believes that food intakes and exposure to sunlight should be enough for most of the population during spring and summer. Vitamin D is available as both a food supplement and as a medicine and the measurements used for the two categories are different. As noted, vitamin D in food supplements is measured in micrograms whilst in medicines it is measured in International Units (shown as IU or iu on packaging). 400iu is the equivalent of 10µg, the recommended intake.
The National Institute for Health and Care Excellence (NICE) recommends people at risk of deficiency should take a 10 microgram vitamin D supplement all year round[ii]. Risk factors for vitamin D deficiency include people:
- Aged 65 years or over
- Who are pregnant and breastfeeding
- Children up to the age of 5
- Who are not exposed to much sunlight (for example living in a care home, office workers and night shift workers) or who cover their skin for cultural reasons
- Who have darker skins who cannot make vitamin D from the sunlight in the UK as quickly or easily as people with paler skins.
Vitamin D deficiency can lead to a disease called rickets. A lack of minerals in the bone means they can become too soft and bend, particularly the bones of the legs and pelvis. In adults, long-term vitamin D deficiency also makes bones soft, but instead of bending, the bones of the legs, pelvis and lower back will ache, and break easily.
Because vitamin D is involved in so many things in our bodies, there are also lots of other symptoms of deficiency. Tiredness and fatigue, low mood and getting more colds and flu can also be indicators that vitamin D levels are too low.
If you are concerned that you may be suffering from low vitamin D, make sure you eat plenty of foods containing vitamin D (see above). Consider taking vitamin D supplements which are widely available at low cost.
Safety and risks
Taking a vitamin D supplement as well as eating foods rich in vitamin D and spending a lot of time outside in sunshine is not a problem. However, do not take more than one supplement containing vitamin D (cod-liver oil is a supplement) as you could exceed the safe limit.
Doses over 100µg are not considered to be safe and in 2018 the UK food supplement industry committed to a voluntary upper level of 75µg to ensure consumer safety. 75µg is the equivalent of 3,000iu. It is not considered advisable to take more than this unless recommended by a healthcare practitioner.
Always choose a supplement tailored to the age group or condition, as fish liver oils and high dose multivitamin supplements often contain vitamin A, too much of which can cause liver and bone problems, especially in very young children, and the elderly. Too much vitamin D, taken for a long time, can lead to high levels of calcium in the blood. This is called hypercalcemia and it can damage the kidneys and the heart.
Although the sun’s ultraviolet rays allow vitamin D to be made in the body you do not have to sunbathe to make vitamin D. Strong sun also burns skin, so it is important to balance making vitamin D with being safe in the sun. Take care to cover up or protect your skin with sunscreen before you turn red or get burnt.
DeLuca HF. History of the discovery of vitamin D and its active metabolites. BoneKEy Reports. 2014;3:479. doi:10.1038/bonekey.2013.213.
 Vitamin D: The Sunshine vitamin International Centre for Well-Being https://icwb.com/health/vitamin-d Accessed 13 Oct 2022
 Schwalfenberg GK, Genuis SJ. Vitamin D, Essential Minerals, and Toxic Elements: Exploring Interactions between Nutrients and Toxicants in Clinical Medicine. The Scientific World Journal. 2015;2015:318595. doi:10.1155/2015/318595.
 Hill TR, Aspray TJ. The role of vitamin D in maintaining bone health in older people. Ther Adv Muscuoloseklet Dis 2017 Apr;9(4):89-95. doi:10.1177/1759720X17692502
 Prietl B, Treiber G, Pieber TR, Amrein K. Vitamin D and Immune Function. Nutrients. 2013;5(7):2502-2521. doi:10.3390/nu5072502.
 Gunton JE, Girgis CM. Vitamin D and muscle. Bone Reports. 2018; 9:120-121 doi.org/10.1016/j.bonr.2018.04.004
 Le TYL, Ogawa M, Kizana E, Gunton JE, Chong JHJ. Vitamin D Improves Cardiac Function After Myocardial Infarction Through Modulation of Resident Cardiac Progenitor Cells. Heart Lung and Circulation. 2018; 27(8): 967-975. doi: org/10.1016/j.hlc.2018.01.006
 Khan A, Dawoud H, Malinski T. Nanomedical studies of the restoration of nitric oxide/peroxynitrite balance in dysfunctional endothelium by 1,25-dihydroxy vitamin D3 – clinical implications for cardiovascular diseases. International Journal of Nanomedicine. 2018; 13:455-466 doi.org/10.2147/IJN.S152822
 Spedding S. Vitamin D and depression: a systematic review and meta-analysis comparing studies with and without biological flaws. Nutrients. 2014 11;6(4):1501-1518 doi: 10.3390/nu6041501
 PHE publishes new advice on vitamin D. Public Health England July 2016. Accessed 25 September 2018. Available from https://www.gov.uk/government/news/phe-publishes-new-advice-on-vitamin-d