Vitamin D deficiency - causes, symptoms and risks

Vitamin D deficiency - causes, symptoms and risks

Author Gill Shaffer Last updated 14th October 2019

  • Health Conditions

After research showed that more than half of people in the UK are vitamin D deficient - including up to 90% of the multiethnic population - the NHS began recommending that every adult in the UK take a supplement during the autumn and winter.

We look at the likely reasons for vitamin D deficiency, highlight the tell-tale signs and symptoms, then explain the potential consequences of not getting enough of this essential nutrient.

  • What is vitamin D?
  • What is vitamin D deficiency?
  • How can I tell if I am deficient in vitamin D?
  • What are the risks of vitamin D deficiency?
  • Summary

What is vitamin D?

Vitamins are a kind of micronutrient that is necessary for life, as they play a part in the complex processes that keep our cells functioning.

People who do not get enough of one of these minerals are at risk of developing serious illnesses. In fact, vitamin D was discovered after scientists realised that poor diet and lack of sunlight was leading to a disease called rickets becoming more common among urban populations in the 19th and early 20th century.

As a substance, vitamin D is a fat-soluble secosteroid that is produced by human skin in the presence of adequate sunlight. It is also obtained through dietary sources, for example oily fish like mackerel, eggs and mushrooms. It was first isolated and described by scientists in 1932.1

Vitamin D acts like a hormone in the body and helps to keep bones strong by regulating calcium and phosphate in the blood, as well as playing a vital role in many other important processes from disease prevention to tissue growth.2,3,4

What is vitamin D deficiency?

Vitamin D is essential to life; if a person’s body does not create enough in contact with sunlight, and if they do not obtain enough from their diet, then they will become deficient. This can have serious health implications.

In the UK, most people can get the vitamin D they need from sunlight during the spring and summer (from April to the beginning of October). However, in the UK the sun is too weak for the human body to generate enough vitamin D during the autumn and winter.

90% of the vitamin D that we need is obtained from the sun and it is difficult to make up this difference from diet alone, so during the autumn and winter the NHS recommends that everyone takes a daily 10 microgram (µg) supplement during this period (note that the recommended dose is different for children).5

Some people are at greater risk of becoming deficient and should take the supplement all year round:

  • People who don’t spend a lot of time in direct sunlight. This includes those who lead indoor-oriented lifestyles, such as older people who find it difficult to get out and about, and people who choose to cover their skin when outdoors.
  • Older adults. The ability to create vitamin D from sunlight exposure decreases as with age.
  • People with dark skin (African, Afro-Caribbean and South Asian descent). Dark skin has a higher level of the pigment melanin in the epidermal layer, which means more protection from UV radiation but slower vitamin D production.
  • Obese people, as subcutaneous fat sequesters more of the vitamin and alters its release into circulation.
  • If you have a condition such as Crohn’s disease or cystic fibrosis you may struggle to absorb some fats. These conditions are associated with low vitamin D, although whether this is a cause or an effect is unknown.6

How can I tell if I am deficient in vitamin D?

If you have a ‘mild’ deficiency there is a good chance that you are not aware of it, even though it may harm you in the long term.

In fact, UK Government figures show that 21% of white people in the UK are deficient, while people with darker skin are even more affected as it is harder for them to generate vitamin D from weak sunlight. Three quarters of Asians and more than half of black people are believed to be deficient.7

Even sunny countries are seeing an uptick in vitamin D deficiency as people adopt a more sedentary, indoor lifestyle.8

You may be able to tell that you have a vitamin D deficiency from the following list of symptoms:

  • Frequent illnesses and/or infections
  • Bone, back or muscle pain
  • Depression
  • Tiredness and fatigue
  • Poor healing from cuts or other injuries
  • Hair loss

What are the risks of vitamin D deficiency?

Vitamin D is essential to life - so essential that every tissue in the body has vitamin D receptors.

As well as developing the symptoms listed above, people who are deficient risk developing debilitating conditions.

  • Children who are lacking in vitamin D may develop rickets. This means that their bones do not get the minerals they need, which causes weakness and makes them more vulnerable to fractures. Rickets often gives sufferers characteristic 'bandy legs'.
  • Adults may develop the adult form of rickets, osteomalacia, which can cause softened bones and pain and are more likely to suffer from bone loss/osteoporosis. Even dental health can be affected.
  • Some studies suggest that deficiency may be linked with an increased risk of developing dementia.9It has also been associated with other mental health issues.10
  • Low vitamin D levels have been connected with increased risk of death from cardiovascular diseases like atherosclerosis.11


Vitamin D is such an important micronutrient that deficiency can cause serious health issues. People who don’t get enough may suffer from weakened bones, and this is especially serious among children. It can be difficult to tell whether you are deficient, but sometimes symptoms such as depression, tiredness and fatigue and frequent illnesses can be a clue.

The NHS recommends that everyone in the UK take a vitamin D supplement during the autumn and winter, and says that people in at-risk groups should take one all year round.


  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. M. F. Holick, H. K. Schnoes, and H. F. DeLuca Identification of 1,25-Dihydroxycholecalciferol, a Form of Vitamin D3 Metabolically Active in the Intestine. Proc Natl Acad Sci U S A. 1971 Apr; 68(4): 803–804.
  3. Reichrath J, Lehmann B, Carlberg C, Varani J, Zouboulis CC. Vitamins as hormones. Horm Metab Res. 2007 Feb;39(2):71-84.
  4. Martineau AR. et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ 2017; 356.
  6. Ham M, Longhi MS, Lahiff C, Cheifetz A, Robson S, Moss AC. Vitamin D levels in adults with Crohn's disease are responsive to disease activity and treatment. Inflamm Bowel Dis. 2014;20(5):856–860. doi:10.1097/MIB.0000000000000016.
  8. Martineau AR. et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ 2017; 356.
  9. Thomas J. Littlejohns, William E. Henley, Iain A. Lang, Cedric Annweiler, Olivier Beauchet, Paulo H.M. Chaves, Linda Fried, Bryan R. Kestenbaum, Lewis H. Kuller, Kenneth M. Langa, Oscar L. Lopez, Katarina Kos, Maya Soni, David J. Llewellyn. Vitamin D and the risk of dementia and Alzheimer disease. Neurology Sep 2014, 83 (10) 920-928; DOI: 10.1212/WNL.0000000000000755
  10. Ghazaleh Valipour, Parvane Saneei, Ahmad Esmaillzadeh, Serum Vitamin D Levels in Relation to Schizophrenia: A Systematic Review and Meta-Analysis of Observational Studies, The Journal of Clinical Endocrinology & Metabolism, Volume 99, Issue 10, 1 October 2014, Pages 3863–3872.
  11. Norman P, Powell J. Vitamin D and Cardiovascular Disease. Circulation Research. 2014;114:379–393