Four key benefits of vitamin D

four dogs with their mouths open

Author Gill Shaffer Last updated 3rd October 2019

  • Ingredients & Nutrition

This essential micronutrient, first discovered in the early 20th century, is absolutely essential for life. Without vitamin D, you can lose the ability to properly regulate the calcium in your bloodstream, which keeps your bones strong. Recent research has also shown that it is important for a whole range of bodily processes.

  • What is vitamin D and why is it important?
  • Bone strength in adults
  • Bone development in children
  • Immune system strength
  • Improved mood
  • How can I get enough vitamin D?
  • Summary
  • References

What is vitamin D and why is it important?

Vitamin D is a vital micronutrient that is necessary for life. Like the other vitamins, scientists first postulated its existence while searching for the cause of a common disease.1

In this case, it was discovered by researchers looking into rickets, a disease that causes weak bones in children.

Today, it is known that rickets is the result of vitamin D deficiency. This is because vitamin D acts as a hormone in the body and helps to regulate calcium and phosphate in the bloodstream, which promotes healthy bones. It is also used in a variety of other ways in the body - it’s so fundamental to the proper functioning of the human body that every tissue has vitamin D receptors.

Vitamin D is produced by our bodies in contact with the UVB radiation in sunlight, but in the UK this only applies from March to September when the sun is strongest. It is also present in a limited range of foods such as oily fish and egg yolks. However, according to the UK government, 21% of White British people are deficient and people with darker skin are even more likely to be affected.

    1. Bone strength in adults

The most important role of vitamin D in the human body is to maintain levels of calcium, which keeps bones strong. Older people who do not get enough vitamin D may develop osteomalacia. This is the name given to rickets in adults.

The bones of people with osteomalacia become softened due to a lack of calcium, phosphate and vitamin D. This prevents the transfer of important minerals into the bones that are needed to keep them strong.2

Vitamin D acts in the intestines to improve absorption of calcium from food and works in the kidneys to encourage the re-use of this important mineral. Instead of being excreted, this calcium can be absorbed again by the bones.

Osteomalacia results in chronic fatigue and bone weakness (osteoporosis)3 - which makes bones more vulnerable to breaks and fractures - and can even cause muscle and bone pain, especially in the spine, legs and pelvis.

     2. Bone development in children

In children, vitamin D is even more vital since their bones are still developing.

Children with a vitamin D deficiency tend to develop long, weak bones that bend when weight is placed on them. This causes the distinctive bow legs seen in rickets.4

      3.  Immune system strength

Vitamin D is known to play a role in the immune system, which protects the body from attack by hostile microorganisms like viruses.

In fact, studies have shown that getting enough vitamin D may protect against viral infections. Researchers have also found a link between vitamin D supplementation and reduced risk of catching the flu or developing a respiratory tract infection.5,6,7

It may even reduce your risk of developing extremely serious conditions like heart disease and multiple sclerosis (MS).8,9

  1. Improved mood

Studies have shown that vitamin D deficiency is linked to low mood, anxiety and even depression.10,11 Research has also tied it to seasonal affective disorder (SAD), a kind of low mood associated with the winter months when people in the UK can’t produce vitamin D from exposure to sunlight.

However, although many studies have been performed, the effect of vitamin D on mental wellbeing is still uncertain.12 The usefulness of vitamin D supplements in this area requires further study.

How can I get enough vitamin D?

The best way to get enough vitamin D is to make sure you spend time outside during the summer months. Even 5-30 minutes in direct sunlight with face, arms and legs exposed to direct sun is enough for most people to produce the vitamin D they need. Of course, you should take reasonable precautions if you have sensitive skin or are at risk of skin cancer.

Eating more foods that contain vitamin D, including oily fish, eggs and fortified breakfast cereals, can also make a difference.

However, it is difficult to get enough from your diet to make up for the deficit caused by like of sunlight during the winter months so the UK government recommends that all adults take a daily 10 microgram (µg) supplement between October and early March.13 People in at-risk groups -- those with darker skin, obesity or an illness that makes it harder to absorb fats, plus those who don’t spend time in direct sunlight or cover themselves -- should take it throughout the year.

The best supplements provide vitamin D in its D3 form, though vegetarians and vegans should make sure that their D3 is derived from lichen rather than animal products. Vitamin D is also easier for your body to absorb if it is taken with oil or fatty foods because it is fat soluble.


Vitamin D is an essential micronutrient that keeps bones strong, can help with the proper functioning of the immune system and may even have an impact on areas such as mood. To ensure you are getting enough you should spend time outdoors, especially in the summer months, eat the right foods that provide you with vitamin D and take the UK government’s advice by using vitamin D supplements from October to early March.


  1. Matthias Wacker and Michael F. Holick, Sunlight and Vitamin D: A global perspective for health. Dermatoendocrinol. 2013 Jan 1; 5(1): 51–108.
  2. Michael F. Holick Resurrection of vitamin D deficiency and rickets. J Clin Invest. 2006;116(8):2062–2072.
  3. Sitta Mdo C, Cassis SV, Horie NC, Moyses RM, Jorgetti V, Garcez-Leme LE. Osteomalacia and vitamin D deficiency in the elderly. Clinics (Sao Paulo). 2009;64(2):156–158.
  4. Reichrath J, Lehmann B, Carlberg C, Varani J, Zouboulis CC. Vitamins as hormones. Horm Metab Res. 2007 Feb;39(2):71-84.
  5. Beard JA, Bearden A, Striker R. Vitamin D and the anti-viral state. J Clin Virol. 2011;50(3):194–200.
  6. Urashima M1, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 May;91(5):1255-60.
  7. Martineau et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ 2017;356:i6583.
  8. Wang TJ, Pencina MJ, Booth SL, et al. Vitamin D deficiency and risk of cardiovascular disease. Circulation. 2008;117(4):503–511.
  9. Kassandra L. Munger, MSc; Lynn I. Levin, PhD, MPH; Bruce W. Hollis, PhD; et al. Serum 25-Hydroxyvitamin D Levels and Risk of Multiple Sclerosis. JAMA. 2006;296(23):2832-2838.
  10. Armstrong, D.J., Meenagh, G.K., Bickle, I. et al. Clin Rheumatol (2007) 26: 551.
  11. Jorde, R. , Sneve, M. , Figenschau, Y. , Svartberg, J. and Waterloo, K. (2008), Effects of vitamin D supplementation on symptoms of depression in overweight and obese subjects: randomized double blind trial. Journal of Internal Medicine, 264: 599-609.
  12. Penckofer S, Kouba J, Byrn M, Estwing Ferrans C. Vitamin D and depression: where is all the sunshine?. Issues Ment Health Nurs. 2010;31(6):385–393.
  13. Vitamins and minerals - Vitamin D - NHS