Vitamin D – The Sunshine Vitamin

Vitamin D

Vitamin D deficiency is a common condition that we encounter in general practice. In the winter months 30-40% of the UK population may be found to be Vitamin D deficient, and even in summer 8% of adults and 13% of adolescents may have low levels.1

Vitamin D is needed to help regulate the body’s calcium and phosphorus levels. These are important to keep your bones, teeth and muscles strong and healthy.

How do we get Vitamin D?

Vitamin D is sometimes referred to as the sunshine vitamin as our body creates active Vitamin D from the UVB rays in sunlight. Between the months of April to September, spending short periods of time outside in sunlight, with uncovered forearms and lower legs, should be sufficient to make enough Vitamin D. It is not possible to give specific recommendations about the duration of sunlight exposure needed to maintain a sufficient Vitamin D level. This is because various factors may affect this, including the time of day, the season, air pollution levels, use of high-factor sunscreen and the colour of your skin.2

It is important to remember that prolonged periods in the sun should still be avoided as it is associated with an increased risk of skin cancer. Children and babies should be kept out of direct strong sunlight and wear sunscreen.

Vitamin D is also found in the diet in oily fish, eggs, red meat and many fortified breakfast cereals, yoghurts and margarines. It is also added to infant formula. However dietary intake alone is unlikely to be sufficient to maintain a normal vitamin D level all year round.

 What are symptoms of low Vitamin D? 

Many people with low Vitamin D may have no symptoms. For others, a low Vitamin D may cause tiredness and generalised muscle aches and pains.

How is Vitamin D important for health? 

Vitamin D is needed for musculoskeletal health as it promotes absorption of calcium from the gut, enables bone mineralisation and is important in muscle function.

Studies have demonstrated that calcium and Vitamin D supplementation is associated with a higher bone mineral density (BMD) and a lower osteoporosis and fracture risk. However, the evidence for Vitamin D alone is less clear and supplemental calcium may not be necessary if you have a well-balanced diet.3,4

For older adults, Vitamin D supplementation may improve muscle strengthen and function, and some studies have suggested this may lead to a lower risk of falls.5 

In addition to bone health, several observational studies have suggested a link between Vitamin D and the prevention of several other diseases including diabetes, cardiovascular disease, asthma, cancer, allergy, multiple sclerosis and autoimmune disease. However, the the Scientific Advisory Committee on Nutrition (SCAN) reviewed this data and did not find enough evidence to draw firm conclusions.6

Despite the SCAN report, research exploring Vitamin D’s anti-inflammatory effects is still on going. Most recently, a Cochrane report has shown that Vitamin D supplementation can reduce severe asthma exacerbations.7

Who is at risk of Vitamin D deficiency?

  • Housebound or care home residents
  • Elderly people with thinner skin
  • People with darker skin
  • People who cover their skin outside (for example for religious beliefs, previous skin cancer, or photosensitivity)
  • Pregnant and breast-feeding women
  • People who live in a country with shortened hours of day light
  • Those who suffer with a medical condition that affects the way their body handles Vitamin D – e.g. inflammatory bowel disease, coeliac disease, obesity and liver and kidney problems
  • People on certain medications – e.g. anti-epileptics and some antiviral medications 

How much Vitamin D do I need?

Although ranges may vary slightly, a general consensus on Vitamin D levels are as follows:8

  • <25 nmol/L – deficient
  • 25-50 nmol/L – insufficient
  • 50-75 nmol/L – adequate
  • >75 nmol/L – optimal

The National guidance issued by the SCAN states that levels of >25 nmol/L are needed for musculoskeletal protection. Levels below this may require a higher level of replacement that can be prescribed by your GP.

How can I be tested for Vitamin D deficiency?

Testing might not be necessary as your GP should be able to advise you if you’re likely to need a supplement. However, if you think you have symptoms suggestive of Vitamin D deficiency your GP or health care professional can arrange a blood test for you. Blood concentration is a good indication of exposure to Vitamin D (both from sunlight and from diet).

Who should take Vitamin D supplements?

In 2016, Public Health England changed their guidance on Vitamin D supplementation.8

They key points are summarised below:

  • Adults should consider taking a daily supplement of 10 μg/400 IU of Vitamin D, particularly during autumn winter months
  • If you are in a “high risk” group, then you should take a daily supplement all year The dose is still the same at 10 μg/400 IU a day (differs from previous guidance)
  • For children aged 1 to 4 years of age, 10 μg/400 IU a day is recommended
  • For babies aged 0 to 1 year, 8.5-10 μg/340-400 IU a day is recommended. However, babies who have more than 500 ml of infant formula a day do not need Vitamin D supplementation as formula is already fortified

If you are concerned that you could be in an “at risk” group, book an appointment with your GP to discuss taking a supplement. 

Can too much Vitamin D be harmful? 

Vitamin D toxicity is normally caused by taking large regular doses of Vitamin D supplements. This can lead to high calcium levels, which may cause abdominal pain, nausea, poor appetite and muscle weakness. It can also lead to kidney and heart problems. This can be avoided by following the guidance above on daily dosing. High dose replacement for Vitamin D deficiency should only be initiated by a health care professional.

In one recent Swiss study, researchers found improved leg function in 65 year olds supplemented with high dose Vitamin D (20 μg) but also interestingly found a higher incidence of falls.9 However this should be interpreted with caution, as it was not the primary outcome of the study and does not provide us with enough evidence to suggest that current UK guidance is unsafe.

For some people, combination Vitamin D and calcium supplements may not be appropriate. If you have a background of cardiovascular disease or kidney stones, speak to your GP before starting supplements.


This article is for information only and should not be used for the diagnosis or treatment of medical conditions. myHealthSpecialist makes no representations as to the accuracy or completeness of any of the information in this article, or found by following any link from this article. Please consult a doctor or other healthcare professional for medical advice.

Dr Anna Cantlay, GP
Dr Anna Cantlay, GP

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