Guide to vitamin D deficiency

Find out what vitamin D deficiency is, how it’s diagnosed, and what the best treatments are to optimise your vitamin D levels.

It is important to have enough vitamin D in the body to function properly. Not enough vitamin D can lead to a deficiency in vitamin D, which may cause rickets in children and bone pain in adults.

To avoid vitamin D deficiency, the Department of Health and Social Care recommends that adults and children over four should get 10 micrograms of vitamin D a day [1].

Taking a supplement or getting outside as much as possible are key factors in preventing deficiency. But what other factors can cause vitamin D deficiency?

What causes vitamin D deficiency?

The amount of vitamin D made in the body depends on a variety of factors, including:

Time spent outdoors

Due to the unpredictable nature of the UK weather, it is no surprise that inadequate exposure to sunlight is one of the most common causes of vitamin D deficiency in the UK.

Most people can make enough vitamin D from being out in the sun for short periods with uncovered forearms or lower legs from late March to the end of September [2].

However, it can be harder to get adequate amounts of vitamin D from spending time outdoors between October and late March.

The UK winter sunlight doesn’t provide enough ultraviolet B (UVB) that the body needs to create vitamin D. Therefore, Public Health England advises all adults and children over five, to consider other sources of vitamin D.


Small amounts of vitamin D are in a variety of foods including [1]:

  • Oily fish
  • Red meat
  • Egg yolks
  • Fortified breakfast cereals

A diet lacking in these types of foods, such as a vegan diet, can result in low vitamin D levels and possibly lead to vitamin D deficiency.

While food can help you meet your vitamin D requirements, it cannot be relied on solely. Instead, it is recommended to get outdoors during summer or consider taking a daily supplement.


Age can be a determining factor in how much vitamin D is in the body. Older people, over the age of 65, have increased rates of vitamin D deficiency [3]. Scientists think that the high levels of vitamin D deficiency could be caused by the body’s ability to absorb, synthesise, and convert vitamin D into its active form, which decreases with age.

Breastfed babies under the age of six months are also at a higher risk of vitamin D deficiency as human milk, may not solely provide enough vitamin D [4]. Therefore, a vitamin D supplement or vitamin D drops are recommended for the first six months of breastfeeding.

Skin tone

People with darker skin, including people of African, African-Caribbean, or South Asian origin, may also be at increased risk of vitamin D deficiency.

There are higher levels of melanin (the pigment that gives the skin colour) in people with darker skin, which lowers the skin’s ability to make vitamin D in response to sunlight.

As a result, people with darker skin may need to spend longer in the sun to produce the same amount of vitamin D as people with lighter skin [5].

More time in the sun is not always the healthiest option though. Up to nine in ten cases of melanoma skin cancer could be prevented by enjoying the sun safely. Cancer Research UK explains how to protect your skin in the sun.


Certain medical conditions affect the body’s ability to absorb vitamins and minerals from food.

With coeliac and Crohn’s disease, the lining of the small intestine can become damaged. The damage can affect the ability of the small intestine to absorb nutrients from food, including vitamin D.

Therefore, people with coeliac and Crohn’s disease are at higher risk of developing vitamin D deficiency and should talk to their doctor about supplementation.

vitamin d blood test product banner

Medical conditions

Kidney and liver disease can also affect vitamin D levels.

In kidney disease, the kidneys become damaged and are less able to make the conversion of vitamin D into the active form that the body uses, resulting in low levels in the body.

The liver works alongside the kidneys to convert vitamin D into the active form that the body needs. Therefore, liver disease can also affect the absorption and synthesis of vitamin D, resulting in a deficiency [6].

Certain medications such as anti-epileptic drugs and weight-loss drugs (such as Orlistat) can also affect how the body processes vitamin D.

Lifestyle factors

Lifestyle factors that affect vitamin D levels include:

  • Obesity – obesity has been linked to vitamin deficiency as scientists think the vitamin D may become trapped inside the fat tissue and less able to circulate in the blood throughout the body [7].
  • Smoking – research has shown that smoking can affect lung function and therefore lessen the levels of vitamin D in the body, also affecting vitamin D’s anti-inflammatory effects [8]
  • Pregnancy – the NHS recommends taking a daily vitamin D supplement if you are pregnant [9] to ensure that you are getting all the vitamins and minerals you need.

What are the symptoms of vitamin D deficiency?

The symptoms of low vitamin D can be subtle, so you may not notice that you are deficient.

Symptoms of vitamin D deficiency include:

  • Tiredness
  • Low mood
  • Irritability
  • Brain fog
  • Hair loss
  • Weight gain
  • Joint and bone pain

What are the effects of vitamin D deficiency on our health?

Vitamin D is vital to the wellbeing of the body. Without it, it cannot function properly.

Vitamin D deficiency can affect:

Bone health

Vitamin D ensures that the body absorbs a healthy amount of calcium and phosphate so that bones and teeth remain healthy. Without vitamin D, the body will only absorb 10-15% of calcium, and 60% of phosphate from food.

If you have low vitamin D, the body cannot take in the right amount of calcium and phosphate. Calcium phosphate is an important mineral that triggers a hormone called parathyroid hormone (PTH), which keeps bones strong and healthy.

If your body has low vitamin D, PTH will increase bone breakdown to release more calcium and phosphate, causing a decrease in bone mineral density (BMD).

This breakdown in the bones leads to osteopenia and osteoporosis, placing a person at a higher risk of fractures.

A severe lack of calcium and phosphate in the bones can lead to weakness and bone deformity; known as rickets in children, and osteomalacia in adults.

Immune system function

As vitamin D plays a crucial role in immune function, it is associated with increased autoimmunity and susceptibility to infection.

When you get a viral infection, such as a common cold, vitamin D helps in the process of creating T cells. The T cells kill the infected host cells, therefore, helping to fight the infection.

One study suggests the benefits of supplementing with vitamin D goes beyond just bone health and could also have significant benefits for the immune system [10].

Other diseases

Research is still ongoing, but having low vitamin D levels is associated with increased risk of many chronic diseases, including:

  • Cardiovascular disease
  • Cancer
  • Diabetes
  • Depression
  • Obesity
  • Pregnancy complications
  • Severe asthma
  • Autism in children [11]

Vitamin D could play a role in the prevention and treatment of conditions including:

  • Diabetes [12]
  • Glucose intolerance [13]
  • Multiple sclerosis [14]

How is vitamin D deficiency diagnosed?

Diagnosing vitamin D deficiency usually starts with a blood test to test how much 25-hydroxy-cholecalciferol test (25 (OH) D) is in your blood.

Testing for 25 (OH) D is the most accurate way to detect how much vitamin D is in your blood because it is the primary circulation form of vitamin D. However, this test may not be as reliable in people with chronic kidney disease.

If you want to test your vitamin D levels at home, you can test your vitamin D levels with our simple finger-prick test.

What are the treatments for vitamin D deficiency?

Vitamin D deficiency is easy to treat, and many of the symptoms can be improved once levels in the body recover.

Treatments for vitamin D deficiency include:

  1.  Vitamin D supplement

The dose of vitamin D that is required will depend on  how low your levels are

  • If your blood results show that you are deficient in vitamin D, you will need to take a supplement. At Medichecks, we advise supplementing with 80 micrograms (4000 IU) per day for 12 weeks.
  • If your vitamin D level is in the insufficient range, we advise you to consider supplementing with 20-50 micrograms per day for 12 weeks.
  • We encourage re-checking your vitamin D level after 12 weeks of supplementation. If your level is then healthy, you can reduce your vitamin D to a maintenance dose of 10 micrograms per day.

Prevention is always better than cure and we may suggest ways that you can optimise your vitamin D levels such as diet and sun exposure, alongside supplementation.

When choosing to supplement, vitamin D3 is preferred over vitamin D2. Vitamin D3 is more efficient in increasing levels in the body as the liver metabolises it better.

You can find vitamin D supplements in most supermarkets, pharmacies, and health shops, as well as online.

  • Pregnant women, women with a child under 12 months, and eligible children up to four years old are entitled to free vitamin tablets through the NHS Healthy Start Scheme.
  • If you have been taking vitamin D supplements for over 12 weeks and your levels have not yet improved, or you are still experiencing symptoms – seek advice from your GP.

Vitamin D supplements should be taken with caution in some circumstances.

If you have any of the following, please seek advice from your doctor before starting vitamin D supplements:

  • Bone disease
  • Renal impairment
  • Kidney stones
  • Any conditions affecting calcium levels
  • Increased sensitivity to vitamin D, due to certain conditions (such as lymphoma, sarcoidosis, or hyperparathyroidism)

If you are pregnant, breastfeeding, or taking any medications, it is recommended to check with your GP before starting any new supplements.

  1.  Spend time in the sun

One of the best ways to improve vitamin D levels is to spend time in the sun.  Spend around 15-20 minutes outside every day, between 11 am and 3 pm.

Wearing a short sleeve top and shorts can help increase absorption.

Between late March and September, reading a book in the garden or going for a daily walk with your family can be great ways to get out and ensure your vitamin D levels are optimal.

Always make sure to stay safe when spending time in the sun. Following guidance from Cancer Research UK can help to protect our skin from harmful damage.

If you have fairer skin that is more sensitive to burning, make sure to start with short periods outside and build up if you can.

Exactly how much time is needed in the sun to make enough vitamin D is unknown, as several factors can affect how vitamin D is made. You should make sure you do not burn in the sun and protect your skin with sunscreen before your skin starts to turn red or burn.

According to studies, sun cream does not affect vitamin D levels [15].

Sunbeds should be avoided as they emit high levels of UVA, which don’t increase vitamin D levels but do increase the risk of cancer.

  1.  Eat good vitamin D food sources

The richest sources of vitamin D can be found in:

  • Oily fish such as salmon. Typically, a 3oz salmon fillet will contain 11-17 micrograms per portion.
  • Mushrooms, especially those exposed to UV light, also contain vitamin D. These mushrooms provide around 7.9 micrograms per half a cup of mushrooms.

However, food should not be relied on as a sole source of vitamin D

As well as ensuring healthy vitamin D levels, it is also essential to maintain adequate dietary calcium intake as we need both for healthy bones and teeth.  If you don’t have much calcium in your diet, you may want to consider a calcium supplement.

Good sources of dietary calcium include:

  • Fortified cereals
  • Cheese
  • Almond milk
  • Tofu

Get tested

Our Vitamin D (25 OH) Blood Test is a simple finger-prick test done from the comfort of your own home. It tests your vitamin D levels to see whether you have low levels that could be contributing to symptoms like low energy and muscle aches and pains.


  1. 2021. Vitamin D. [online] Available at: <> [Accessed 22 December 2021].
  2. 2021. How to get vitamin D from sunlight. [online] Available at: <> [Accessed 22 December 2021].
  3. Boucher BJ. The problems of vitamin d insufficiency in older people. Aging Dis. 2012 Aug;3(4):313-29. Epub 2012 Jun 6. PMID: 23185713; PMCID: PMC3501367.
  4. Balasubramanian S. Vitamin D deficiency in breastfed infants & the need for routine vitamin D supplementation. Indian J Med Res. 2011 Mar;133(3):250-2. PMID: 21441676; PMCID: PMC3103147.
  5. 2021. How to get vitamin D from sunlight. [online] Available at: <> [Accessed 22 December 2021].
  6. Marangoni, F., Cetin, I., Verduci, E., Canzone, G., Giovannini, M., Scollo, P., Corsello, G. and Poli, A., 2016. Maternal Diet and Nutrient Requirements in Pregnancy and Breastfeeding. An Italian Consensus Document. Nutrients, 8(10), p.629.
  7. Vimaleswaran, K., Berry, D., Lu, C., Tikkanen, E., Pilz, S., Hiraki, L., Cooper, J., Dastani, Z., Li, R., Houston, D., Wood, A., Michaëlsson, K., Vandenput, L., Zgaga, L., Yerges-Armstrong, L., McCarthy, M., Dupuis, J., Kaakinen, M., Kleber, M., Jameson, K., Arden, N., Raitakari, O., Viikari, J., Lohman, K., Ferrucci, L., Melhus, H., Ingelsson, E., Byberg, L., Lind, L., Lorentzon, M., Salomaa, V., Campbell, H., Dunlop, M., Mitchell, B., Herzig, K., Pouta, A., Hartikainen, A., Streeten, E., Theodoratou, E., Jula, A., Wareham, N., Ohlsson, C., Frayling, T., Kritchevsky, S., Spector, T., Richards, J., Lehtimäki, T., Ouwehand, W., Kraft, P., Cooper, C., März, W., Power, C., Loos, R., Wang, T., Järvelin, M., Whittaker, J., Hingorani, A. and Hyppönen, E., 2013. Causal Relationship between Obesity and Vitamin D Status: Bi-Directional Mendelian Randomization Analysis of Multiple Cohorts. PLoS Medicine, 10(2), p.e1001383.
  8. Lange, N., Sparrow, D., Vokonas, P. and Litonjua, A., 2012. Vitamin D Deficiency, Smoking, and Lung Function in the Normative Aging Study. American Journal of Respiratory and Critical Care Medicine, 186(7), pp.616-621.
  9. 2021. Vitamins, minerals and supplements in pregnancy. [online] Available at: <> [Accessed 22 December 2021].
  10. Aranow, C., 2011. Vitamin D and the Immune System. Journal of Investigative Medicine, 59(6), pp.881-886.
  11. Wang, H., Chen, W., Li, D., Yin, X., Zhang, X., Olsen, N. and Zheng, S., 2017. Vitamin D and Chronic Diseases. Aging and disease, 8(3), p.346.
  12. Aljabri, K., Bokhari, S. and Khan, M., 2010. Glycemic changes after vitamin D supplementation in patients with type 1 diabetes mellitus and vitamin D deficiency. Annals of Saudi Medicine, 30(6), pp.454-458.
  13. Parildar, H., Cigerli, O., Unal, A., Gulmez, O. and Demirag, N., 2013. The impact of Vitamin D replacement on Glucose Metabolism. Pakistan Journal of Medical Sciences, 29(6).
  14. Sintzel, M., Rametta, M. and Reder, A., 2017. Vitamin D and Multiple Sclerosis: A Comprehensive Review. Neurology and Therapy, 7(1), pp.59-85.
  15. Passeron, T., Bouillon, R., Callender, V., Cestari, T., Diepgen, T., Green, A., Pols, J., Bernard, B., Ly, F., Bernerd, F., Marrot, L., Nielsen, M., Verschoore, M., Jablonski, N. and Young, A., 2019. Sunscreen photoprotection and vitamin D status. British Journal of Dermatology, 181(5), pp.916-931.

Related tests