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Vitamin D Deficiency

What is vitamin D?

Vitamin D is important for good health, growth and strong bones.  It is a fat-soluble vitamin which means that it is absorbed with ingested dietary fat.1 Fat-soluble vitamins are stored in moderate amounts from the gastrointestinal tract.2 Until very recently, vitamin D deficiency wasn’t thought to be very common.  However, several recent research studies are proving that this is not the case.3 More than half the adults of the UK were shown to have not enough vitamin D in a recent study4 with about 9 in 10 adults in the UK of South Asian origin having a possible vitamin D deficiency.5

Vitamin D is mostly made in the skin when you are exposed to sunlight. In the UK you need around 20 minutes of sunlight on the face and forearms around the middle of the day, 2-3 times a week should be enough for your body to make enough vitamin D. People with pigmented skin and the elderly will need much more than this.6

Most people are unaware of the problem and do not realise that they are deficient.

Vitamin D can be found in some foods such as tuna, mackerel, sardines and fish liver oils, beef liver, cheese and egg yolks but only in very small amounts.1 Some foods have vitamin D added such as breakfast cereals, baby formula and margarine.

What does vitamin D do?

Vitamin D maintains adequate calcium and phosphate levels to keep bones healthy and strong.1 Vitamin D has other roles in the body, including helping with cell growth, neuromuscular and immune function and reduction of inflammation.1 There is also some evidence that it helps to prevent cancer, diabetes and heart disease.6

A mild lack of vitamin D can cause general aches and pains6,7 while a more severe lack can cause serious problems such as rickets in children and osteomalacia in adults.7

Who is likely to become vitamin D deficient?

Basically, anyone in the UK can become deficient. Being in the northern hemisphere, the UK doesn’t get as much sunlight as southern countries.

People who are strict vegetarians or vegans or people who do not eat fish are more likely to become vitamin D deficient. There are certain groups of people, though, who may need extra vitamin D – growing children, pregnant and breastfeeding women, people over the age of 65, people who do not expose their skin to the sun, people who have pigmented skin (people with darker skin produce less vitamin D) and babies who are being breastfed (because there is very little vitamin D in breast milk).1,8

What are the symptoms of vitamin D deficiency?

The symptoms can be very vague such as tiredness and general aches and pains which can often be put down to other things such as being very busy or run down and therefore the problem is often missed.  In most cases, the thought of having a vitamin deficiency never occurs. However, if the deficiency is allowed to progress, more symptoms show themselves.

In babies and children:9

  • muscle spasms (cramps), seizures and breathing difficulties due to low levels of calcium
  • soft skull or leg bones, bow-leggedness, bone pain in legs, muscle pains or muscle weakness (rickets)
  • poor height growth and possible reluctance to walk
  • late teething
  • irritability
  • infections

In adults:8

  • osteomalacia, which can cause severe pain and weakness which can make it difficult to climb stairs and get up from the floor or a low chair
  • painful bones when pressed, especially in the ribs or shin bones, possible hairline fractures, bone pain in lower back, hips, pelvis, thighs and feet

Concerning findings in a 2019 research paper showed that maternal vitamin D deficiency in the first trimester of pregnancy was associated with an elevated risk of gestational diabetes mellitus. It was found also that the association was stronger for women who were persistently deficient through the second trimester. The authors stated that “Assessment of vitamin D status in early pregnancy may be clinically important and valuable.”10

How does my doctor diagnose vitamin D deficiency?

Your doctor may suspect you have vitamin D deficiency from your medical history, your symptoms and/or your lifestyle.  In your bloodstream, vitamin D2 and vitamin D3 are converted into a form of vitamin D known as 25 hydroxyvitamin D, also known as 25(OH)D.  Your doctor may do a serum 25[OH]D test as well as check your calcium, phosphate and liver function.11

For children, if rickets is suspected, a wrist X-ray may be done.12

How is vitamin D deficiency treated?

For a mild deficiency, you can increase your vitamin D levels by simply being outside in the sun.

The main treatment for vitamin D deficiency, however, is to take vitamin D supplements. Public Health England has issued guidance stating that adults and children should take a daily supplement containing 10mcg (400iu) of vitamin D, particularly during autumn and winter.13,14

Which form of vitamin D should I take?

There are different forms of supplements:14

  • vitamin D2 (ergocalciferol or calciferol) – a plant product
  • vitamin D3 (cholecalciferol) -– this is the form naturally produced by the skin and is the most efficient form to increase levels. Some doctors feel that D3 is best form to take

Vitamin D comes in different forms – injections, liquid or tablets. You will need to discuss the best form for you with your doctor.  Treatment can depend on the situation, age and severity of the deficiency. Vitamin D is also available combined with calcium.  Your doctor needs to check to see if you are calcium deficient too before prescribing these for you.

  • An injection of vitamin D may be given if the deficiency is severe15
  • High-dose tablets or liquids are usually given for serious deficiency, can be taken daily, weekly or monthly depending on your situation and are good for quick improvement12
  • Once the deficiency has been treated, an ongoing dosage of 10mcg should prevent deficiency from returning12

Vitamin D warnings

There are certain situations where you need to be cautious:

  • Vitamin D has interactions with certain medications such as digoxin and steroids among others16
  • If you have other medical conditions such as kidney stones discuss supplementation with your doctor17
  • If you have high calcium levels vitamin D should not be taken as it may increase your calcium levels further
  • If you are taking a medication that interferes with vitamin D such as carbamazepine and fluoxetine18

Does vitamin D have any side effects?

Side effects from vitamin D are rare but in very high doses it can raise calcium levels1 in the blood giving symptoms such as thirst, passing a lot of urine, nausea or vomiting, dizziness and headaches.19 If you have these symptoms, you should see your GP immediately so that your calcium level can be checked.

Is vitamin D connected with thyroid disorders?

Vitamin D has been directly connected to autoimmune thyroid disease.20 Evidence also suggests that vitamin D can play a role in reducing the occurrence of other autoimmune diseases too.21 It is therefore recommended that patients suffering from hypothyroidism are tested for vitamin D deficiency to establish if vitamin D supplementation could help.


People with vitamin D deficiency usually respond well to treatment although it can take some time, especially if it was a severe deficiency.  If the deficiency was severe enough to cause rickets or osteomalacia, it may have caused permanent bone deformities if treatment was delayed.22

If you are worried that you may have vitamin D deficiency, ask your doctor to test your levels especially if you are planning a pregnancy. Alternatively, you can purchase a vitamin D test privately.

Vitamin D and COVID-19

Read our new article on vitamin D and COVID-19.

For more support check out our online community:


  1. Vitamin D – Factsheet for health professionals
    National Institutes of Health
  2. All you need to know about fat-soluble vitamins
    Medical News Today
  3. What Have We Learned About Vitamin D Dosing?
    Joseph Pizzorno, ND
  4. Hypovitaminosis D in British adults at age 45 y: a nationwide cohort study of dietary and lifestyle predictors
    Hyppönen E, Power C.
    (Am J Clin Nutr. 2007 Mar;85(3):860-8)
  5. Distribution analysis of vitamin D highlights differences in population subgroups: preliminary observations from a pilot study in UK adults
    Pal BR, Marshall T, James C, Shaw NJ
    J Endocrinol 2003 Oct;179(1):119-29.
  6. Vitamin D deficiency
    Dr Louise R Newson – 14 December 2016
  7. Vitamin D Deficiency in Adults: When to Test and How to Treat
    Kurt A. Kennel, MD, Matthew T. Drake, MD, PhD, and Daniel L. Hurley, MD
  8. Vitamin D
  9. Vitamin D deficiency in children
    NHS – Nottingham University Hospitals
  10. Vitamin D status during pregnancy and the risk of gestational diabetes mellitus: A longitudinal study in a multiracial cohort
    Jin Xia MS Yiqing Song ScD  Shristi Rawal PhD  Jing Wu MD  Stefanie N. Hinkle PhD  Michael Y. Tsai PhD Cuilin Zhang MD
  11. Vitamin D test
  12. Vitamin D Deficiency including Osteomalacia and Rickets
    Dr Colin Tidy, Reviewed by Prof Cathy Jackson (Last edited 29 Jun 2015)
  13. Vitamin D deficiency in adults – treatment and prevention
  14. Vitamin D in Children
  15. Health claims about vitamin D examined
    Nursing Times (24 June 2013)
  16. Vitamin D
    Mayo Clinic Staff
  17. Vitamin D Intake and the Risk of Incident Kidney Stones
    Ferraro, P. M., Taylor, E. N., Gambaro, G., & Curhan, G. C. (2017)
    The Journal of Urology, 197(2), 405–410. doi:10.1016/j.juro.2016.08.084
  18. Drug-vitamin D interactions: a systematic review of the literature
    Robien K, Oppeneer SJ, Kelly JA, Hamilton-Reeves JM.
    Nutr Clin Pract. 2013 Apr;28(2):194-208
  19. What is vitamin D toxicity? Should I be worried about taking supplements?
    Mayo Clinic – Katherine Zeratsky, R.D., L.D.
  20. The Role of Vitamin D Deficiency in Thyroid Disorders
  21. Vitamin D Deficiency and its Association with Thyroid Disease
    Amal Mohammed Husein MackawyBushra Mohammed Alayed, and Bashayer Mater Al-rashidi
    Int J Health Sci (Qassim)
    . 2013 Nov; 7(3): 267–275.
  22. Everything you need to know about rickets
    Stephanie Brunner B.A. (Last updated Tue 19 December 2017)

Date updated: 17.08.21 (V1.5)
Review date: 06.06.22

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