Vitamin D

Written by Dr Claudia Pastides, 8th March 2019

This page explains the role of vitamin D, who supplementation is advised for, how much we should be taking and why vitamin D is recommended.

What is vitamin D?

Vitamin D is a unique vitamin because you can find it in both:

  1. Food, in particular oily fish (tuna, mackerel, salmon) and foods fortified with vitamin D.
  2. Your skin, as you make vitamin D when you skin is exposed to the UVB rays of sunlight.

If we’re going to get scientific - it isn’t just a vitamin, but a hormone that binds to vitamin D receptors in the body and has a very important role in the metabolism of bone.

The role of vitamin D

Traditionally, vitamin D has been responsible for the regulation of phosphate and calcium, and the healthy development and maintenance of strong bones. We’ve known for some time now that low vitamin D levels in childhood cause deformed bendy bones (a condition called rickets) and fragile painful bones in adults (osteomalacia).

However the discovery of vitamin D receptors on at least 36 tissues in the body (including breast cells, cancer cells, the placenta, the immune system, ovaries, the brain and prostate to name just a few)1 has led to a wealth of speculation around what else vitamin D might be responsible for.

What happens when vitamin D levels are low?

Very low levels of vitamin D can cause symptoms such as:

  • Bone pain in the lower back, pelvis and legs
  • Muscle aches and weakness (especially in the thighs)
  • Widespread pain that lasts for many months

There is as yet not enough good quality evidence to say how low vitamin D levels affect other parts of the body beyond the musculoskeletal system (muscles and bones).

Checking your vitamin D level

Your GP will often request a vitamin D blood test if you have the symptoms mentioned above, or in certain instances, such as:

  • If you’ve got a bone condition (osteomalacia, osteoporosis, Paget’s disease).
  • If you have symptoms of low calcium levels (numbness, muscle spasms, seizures)
  • If you have had a fall.

The GP won’t routinely check your vitamin D level unless there is a clinical indication to do so and this is because studies have shown that if we ask the general British public to have a vitamin D blood test, a large proportion of people of all ages will have low vitamin D levels.

The National Diet and Nutrition Survey found low vitamin D levels in2,3:

  • 23% of people aged 19–64 years
  • 21% of people aged 65 years and over

In the months of January to March, this increased to:

  • 30% of people aged 65 years and over
  • 40% of people aged 19–64 years

Public Health England have taken the stance that a little bit of vitamin D will do no harm and likely prove beneficial There is therefore no need to subject every single asymptomatic individual to a blood test.

What is a healthy vitamin D level?

Although there is no clear consensus, the National Institute of Clinical Excellence, together with the Institute of Medicine and the National Osteoporosis Society advise the following:

  • Less than 30nmol/L - Deficient
  • 30 - 50 nmol/L - May be inadequate for some people
  • Greater than 50nmol/L - Sufficient for most people

People that are found to be deficient in vitamin D will usually be treated with high dose vitamin D tablets by their GP as this group is considered more at risk of bone disease. Those with inadequate levels might be prescribed high doses of vitamin D or be recommended to purchase vitamin D over the counter, depending on whether they have other health conditions and if the GP thinks it would be helpful.

Keeping your vitamin D levels healthy

Our diet does not provide us with all of the vitamin D that we need. The majority of vitamin D is produced by exposure of our skin to the sun.

Our problem in the UK is that, during autumn and winter, there is very little UVB sunlight getting through to us and, as a result, many are likely to be low in vitamin D during these seasons in particular, so it is advisable to take a supplement.

For information on how to get vitamin D safely from sunlight, click here

How much vitamin D should you take?

The table below summarises who is recommended a vitamin D supplement, what dose (in International Units and micrograms) how often and why, in accordance with the 2016 Public Health England guidance4:

How muchHow oftenWhy
International Units (IU)Micrograms (mcg)
Babies (aged 0-1)220 - 4005.5 - 10Daily if exclusively breastfed or if receiving less than 500ml of formula milk/dayBreast milk vitamin D levels will be low if the mother’s levels are low. Formula milk is fortified with vitamin D
Young children aged 1-440010DailyFor bone health and the prevention of rickets
Children aged 5 and over40010Daily in autumn and winterInsufficient sunlight exposure to make enough vitamin D
Pregnant women40010Daily throughout pregnancyTo make sure the mother’s vitamin D levels are healthy and the baby isn’t born low in vitamin D
Breastfeeding women40010Daily from baby’s birthThe vitamin D level in breast milk depends on the mother’s vitamin D levels
People with little exposure to the sun or who always cover their skin when outdoors40010All year roundInsufficient sunlight exposure to make enough vitamin D
Ethnic minority groups with dark skin (African, Afro-Caribbean and South Asian backgrounds)40010All year roundSkin type requires more sunlight in order to make adequate levels of vitamin D and there isn’t enough of it in the British summer to do so
All adults40010During autumn and winterInsufficient sunlight exposure to make enough vitamin D

Free vitamins via Healthy Start

If you’re pregnant, are a woman with a child under the age of 1 or have children aged between 4 weeks and 4 years old - you might be eligible for free vitamins.

For more information on Healthy Start and to check whether you are eligible, visit the website and you can find your local Healthy Start vitamins service.

More information about vitamin D

The British Dietetic Association

How to get vitamin D from sunlight


Where can I buy vitamin D supplements from?

Most pharmacies and health food shops sell vitamin D supplements. Make sure to check the amount of vitamin D in the supplements that you choose as they can vary widely.

Can I have too much vitamin D?

Yes. Taking more than the recommended amount can prove toxic and cause unpleasant symptoms such as nausea and vomiting. Long term exposure to high doses may lead to kidney and heart problems.

Will sunbeds or sunbathing help increase my vitamin D level?

Too much UVB increases your risk of skin cancer. Also, if your skin produces a large amount of vitamin D, your body destroys the excess vitamin D.