All you need to know about Vitamin D

Professor Edel O’Toole


Vitamin D is a vitamin which is essential for our health and well-being.  Individuals with ichthyosis, in particular ARCI, including CIE/lamellar/harlequin ichthyosis, and epidermolytic ichthyosis, are at risk of Vitamin D deficiency.    Vitamin D is particularly important for bone health, but in recent years has been shown to play an important role in boosting the immune system.    90% of our Vitamin D is synthesized in our skin by exposure to sunlight.  Only about 10% comes from food. 

Figure 1:  How the body processes Vitamin D made in the skin.  Adapted from:


Vitamin D containing food

Oily fish (sardines, herring, trout, tuna, salmon, mackerel)

Egg yolk

UV irradiated mushrooms (usually dried or put mushrooms in a sunny window)

Cod liver oil


Infant formula milk, most margarines and some cereals (have added Vitamin D)


What is a healthy level of vitamin D?

We get 90% of our vitamin D from sunshine, 10% from food and/or dietary supplements. There are two forms of vitamin D: sunshine and animal foods provide vitamin D3 while plant food sources and fortified foods eg infant formula supply vitamin D2.   The only way to know if you are getting enough is a blood test. The report usually gives Vitamin D3 level, sometimes Vitamin D2 level or total vitamin D level which is Vitamin D3 plus Vitamin D2.  The result is given as either nanomoles per liter (nmol/L) or nanograms per milliliter (ng/mL). One nmol/L is the same as 0.4 ng/mL.

Vitamin D level (nmol/L)

Vitamin D level (ng/ml)

Is it enough?

Health outcome

>125 nmol/L

>50 ng/mL

Too high

Might cause health problems

75 nmol/l

30 ng/ml

Ideal to aim for

Optimal bone and overall health

50 nmol/L

20 ng/mL


Sufficient for bone and overall health

>30 nmol/L but less than 50nmol/L

12-20 ng/ml


Insufficient for bone and overall health

<30 nmol/L

<12 ng/mL


Might weaken your bones and affect your health


Who gets vitamin D deficiency?

Vitamin D deficiency means that there is not enough vitamin D in your body. This may be for one of 3 reasons (all three may apply to individuals with ichthyosis, depending on their circumstances):

You have an increased need for vitamin D

  • Growing children, pregnant women, and breast-feeding women need extra vitamin D because it is required for growth. Patients with severe forms of ichthyosis eg CIE/lamellar are often in this category.  We do not understand why.

Your body is unable to make enough vitamin D

  • People who get very little sunlight on their skin are at risk of vitamin D deficiency. This is more of a problem in the northern parts of the world (including the UK) where there is less sun.

In particular:

  • People who are in hospital or stay in their home.
  • People who cover up a lot of their body when outside.
  • The strict use of sunscreen may increase the risk of vitamin D deficiency, particularly if high sun protection factor (SPF) creams (factor 15 or above) are used. However, there is no evidence that the normal use of sunscreen does actually cause vitamin D deficiency in real life. Everyone, especially children, should always be protected from sunburn.
  • People who have darker skin are not able to make as much vitamin D.
  • Some medical conditions can affect the way the body handles vitamin D. People who are overweight or obese, people with Crohn's disease, coeliac disease, and some types of liver and kidney disease, are all at risk of vitamin D deficiency.

Your diet does not provide enough vitamin D

  • Vitamin D deficiency is more likely to occur in people who follow a strict vegetarian or vegan diet, or a non-fish-eating diet.

Symptoms of Vitamin D deficiency

Adults:  Many people have no symptoms, or may complain of symptoms such as tiredness, hair loss or aches and pains.  In more severe deficiency, there may be bone pain and muscle weakness. 

Children:  Children with severe deficiency may have soft skull or leg bones. Their legs may look curved (bow-legged). They may also complain of bone pains, often in the legs, and muscle pains or muscle weakness. This condition is known as rickets.

Poor growth. Height is usually affected more than weight. Affected children might be reluctant to start walking.

Tooth delay. Children with vitamin D deficiency may be late teething, as the development of the milk teeth has been affected.

Children with vitamin D deficiency are more prone to infections.

Prevention of Vitamin D deficiency

Public Health England recommends that everyone over the age of 1 year takes Vitamin D 400 iu daily (10 µg daily) between October and April.   This might not be enough if you don’t get out in the sunshine in summer.

Treatment of Vitamin D deficiency  

Vitamin D supplements are usually given as Vitamin D3, which I will refer to as Vitamin D.  1000 iu= 25 µg

18 months- 12 years  Vitamin D 3000 iu (75 µg) daily for 3 months, then 1000 iu (25 µg) daily to prevent recurrence

Over 12 years  Vitamin D 5000 iu (125 µg) daily for 3 months, then 1000 iu (25 µg) daily to prevent recurrence

However, someone with ichthyosis with darker skin who covers up might need Vitamin D 3000 iu (75 µg) daily for life.   This can be taken as 3000 iu daily or alternatively 20,000 iu weekly. 

I would advise patients with ichthyosis to request their doctor to check their vitamin D level, treat any deficiency as above and then repeat bloods in 1 year.  If adequate, should continue on vitamin D 1000 iu daily.    If still <30 nmol/L probably needs 3000 iu daily, if more than 30 but less than 50 nmol/L 2000 iu daily.   All individuals who have inadequate or deficient Vitamin D levels need to stay on Vitamin D for life.   


Examples of Vitamin D supplements available



For infants and toddlers up to the age of 4, Dalivit or Abidec drops can be used.  Some families with lower incomes will qualify for these under the Healthy Start scheme.  In general GPs will prescribe high dose vitamin D for those who are deficient, but they may not continue to prescribe preventative supplements.  Vitamin D 1000 iu daily capsules are available cheaply from Boots or Sainsburys. 

Some individuals who need a higher dose of vitamin D opt to use DLUX spray 3000 iu daily (1 spray under tongue) or 20,000 iu capsules, one weekly. 

Are there any risks to taking vitamin D supplements?

In general, in children over the age of 12 and adults, Vitamin D up to 4000 iu daily will do no harm.

Care is needed with vitamin D supplements in certain situations:  If you are taking certain other medicines: digoxin (for an irregular heartbeat - atrial fibrillation) or thiazide diuretics such as bendroflumethiazide (commonly used to treat high blood pressure). In this situation, avoid high doses of vitamin D, and digoxin will need monitoring more closely.

If you have other medical conditions: kidney stones, some types of kidney disease, liver disease or hormonal disease. Discuss with your doctor.

Vitamin D should not be taken by people who have high calcium levels or certain types of cancer.  Again, discuss with your doctor.

Vitamin D and Covid19

There is evidence that individuals hospitalized with Covid19 have lower levels of Vitamin D.  This is another good reason to ensure that your Vitamin D levels are adequate and take Vitamin D supplements. 

My experience of vitamin D

Most of my patients over the age of 12 with ichthyosis who have previously been deficient are advised by me to take vitamin D 20,000 iu weekly.  Many of them probably take it about half of the time ie every 2 weeks and in general those that take it have a normal vitamin D level and feel better for taking it.  Some patients have had an improvement in their general wellbeing and think that they are a bit less red when they take vitamin D regularly.  I take vitamin D 20,000 iu weekly myself and a box of 30 capsules usually lasts me over a year ie I probably take it every 2 weeks.   I know when my vitamin D is getting low because my left hip gets sore!

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Acknowledgement:  I am grateful to Professor Celia Moss for commenting on this short article. 

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