Overview of vitamin D
As we’re spending more time in our homes, a daily dose of Vitamin D has never been more important to help you and your family stay well. Find out all about vitamin D, including what it does, how much you need, where to find it, and who might need to supplement their diet
What is vitamin D and what does it do?
Vitamin D is known as the sunshine vitamin, as we get roughly 90% of our intake by exposing our skin to sunlight.
In autumn and winter, the sun isn’t strong enough to make all the vitamin D we need, so around 20% of people in the UK have low vitamin D levels.1
There are two main types:
- D2 – found in plants and often used in fortified foods
- D3 – found in animal products and is the type your skin makes using sunlight
Both types carry out the same roles – to maintain healthy bones and support your immune system – but vitamin D3 is thought to be better absorbed and used by the body.2
Very few foods are naturally rich in vitamin D but the main sources are oily fish, egg yolks and fortified cereals.3 Vitamin D exists as a vitamin in foods but as a hormone in our bodies.
A lack of vitamin D can lead to weak bones. In children, this presents as rickets, while in adults a deficiency can cause osteomalacia or osteoporosis.4
Functions of vitamin D
What does vitamin D do in the body?
Vitamin D helps bones and cells absorb calcium and phosphorus,5 which are vital for strong bones and teeth. Vitamin D also helps with muscle function, which can reduce the risk of falls in elderly people.
We also need vitamin D for:6
- healthy cell growth
- normal immune system function
- regulating levels of calcium and phosphorous in the blood
How much vitamin D do I need?
We need 10mcg of vitamin D a day.7 Between April and September, around 15-20 minutes of direct sunlight can provide you with enough vitamin D, but this will vary according to your skin type.8
In autumn and winter the sun isn’t strong enough in the UK for us to produce vitamin D, so it’s recommended that everyone from the age of one takes a daily supplement of 10mcg.9
For vulnerable groups who don’t get enough sunshine – people with darker skin, those aged 65 or older, people who cover up for religious or cultural reasons, for example – a year-round vitamin D supplement is advised.10
How much vitamin D do children need?
Babies under the age of one need 8.5mcg to 10mcg a day. Older children need the same amount of vitamin D a day as adults.11
Vitamin D foods
Which foods are the best sources of vitamin D?
Foods that contain vitamin D are:12,13
- oily fish, such as sardines and salmon
- fish and algae oil supplements
- red meat, especially liver
- fortified plant milks
- fortified cereals
Vitamin D deficiency
What are the symptoms of a vitamin D deficiency?
A vitamin D deficiency can lead to rickets in children and osteomalacia or osteoporosis in adults.14 It causes the bones to become soft and weak, often leading to deformities and a higher risk of fractures.
Other symptoms include:15
- growth problems
- bone and joint aches
- greater risk of infections
- gum disease
What happens if I consume too much vitamin D?
Your body won’t make too much vitamin D via sunlight, but consuming too much through food or supplements over a long period of time can weaken bones and kidneys.16
The government advises 10mcg of vitamin D a day as an optimal level,17 but the safe upper level (how much you can consume without harming your health) is 100mcg.18
Vitamin D supplements
When should I take vitamin D supplements?
The NHS says everyone over the age of one should think about taking a daily vitamin D supplement (10mcg), especially during autumn and winter.19 Vulnerable groups are advised to take a supplement year-round.
When choosing a supplement, vitamin D3 is better at improving vitamin D levels in the blood than D2.20
Should children take vitamin D supplements?
The government recommends that breastfed babies under one should take a daily supplement of 8.5mcg year-round. Formula-fed babies (500ml or more a day) don’t need a supplement, as formula is fortified with vitamin D.21
Should women take a vitamin D supplement during pregnancy?
Yes. Pregnant and breastfeeding women should take 10mcg every day, as normal levels of vitamin D are important during pregnancy. 22 Choose a supplement that is specially formulated for pregnancy to avoid the risk of consuming too much vitamin A.
What are the potential benefits of taking a vitamin D supplement?
The government says around 25% of teenagers and adults in the UK have low levels of vitamin D, which puts them at risk. As there are so few food sources of vitamin D, and sun exposure can be unreliable, supplements are considered a safe way to prevent a deficiency.23
A 2013 review of evidence concluded that a vitamin D supplement could help protect against coughs and colds,24 while a separate 2013 study reported that women with lower levels of vitamin D experience tiredness and low energy.25
Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies.
Written by Rosalind Ryan on October 23, 2018
Reviewed by Dr Carrie Ruxton PhD on November 3, 2018
1. Gov.UK. National Diet and Nutrition Survey. Available from: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/551352/NDNS_Y5_6_UK_Main_Text.pdf
2. Food Standards Agency. Safe Upper Levels for Vitamins and Minerals. Available from: https://cot.food.gov.uk/sites/default/files/cot/vitmin2003.pdf
3. NHS. Vitamin D. Available from: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
4. As Source 2
5. Nair R, Maseeh A. Vitamin D: The “sunshine” vitamin. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3356951/
6. National Institutes of Health. Vitamin D. Available from: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
7. As Source 3
8. As Source 3
9. NHS. The new guidelines on vitamin D – what you need to know. Available from: https://www.nhs.uk/news/food-and-diet/the-new-guidelines-on-vitamin-d-what-you-need-to-know/
10. As above
11. As Source 3
12. BDA. Food Fact Sheet: Vitamin D. Available from: https://www.bda.uk.com/foodfacts/VitaminD.pdf
13. Taylor Jones. 9 Healthy Foods That Are High in Vitamin D. Available from: https://www.healthline.com/nutrition/9-foods-high-in-vitamin-d#section2
14. HSIS. Vitamin D (Cholecalciferol). Available from: https://www.hsis.org/a-z-food-supplements/vitamin-d-cholecalciferol/
15. As above
16. As Source 14
17. As Source 3
18. As Source 2
19. As Source 9
20. Atli Arnarson. Vitamin D2 vs. D3: What’s the Difference? Available from: https://www.healthline.com/nutrition/vitamin-d2-vs-d3
21. As Source 9
22. NHS. Vitamins, supplements and nutrition in pregnancy. Available from: https://www.nhs.uk/conditions/pregnancy-and-baby/vitamins-minerals-supplements-pregnant/
23. Scientific Advisory Committee on Nutrition. Vitamin D and health. Available from: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/537616/SACN_Vitamin_D_and_Health_report.pdf
24. Bergman P, et al. Vitamin D and Respiratory Tract Infections: A Systematic Review and Meta-Analaysis of Randomized Controlled Trials. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3686844/
25. Ecemis GC, Atmaca A. Quality of life is impaired not only in vitamin D deficient but also in vitamin D-insufficient pre-menopausal women. Available from: https://www.ncbi.nlm.nih.gov/pubmed/23511484