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Vitamin D & vitamin D deficiency

Vitamin D plays many important roles for our health, and is known as the ‘sunshine vitamin’. It helps us absorb calcium to keep our bones strong, supports our immune system to fight off viruses and bacteria, and impacts our mental health.

What is vitamin D?

Vitamin D is a hormone that forms in the skin as a result of exposure to the sun or another source of UVB radiation. The body can also get vitamin D through foods or dietary supplements absorbed by the gut.

Vitamin D is stored in the liver and fatty tissue, and comes in two forms. Vitamin D3 is made with sunlight, and is also found in fatty fish, meat and eggs. Vitamin D2 is found in mushrooms and certain vegetables.

Although more research is needed to define all functions of vitamin D, we know it affects many aspects of our physical and mental health. Our bodies have vitamin D receptors in the cells of our skin, bones, brain, thyroid gland and kidneys. Vitamin D also affects growth by helping our cells to multiply.

How do we get vitamin D?

When your skin is exposed to sunlight, vitamin D is created and stored in your body. The amount of vitamin D depends on the time of year, how much time you spend in the sun, and where you are in the world.

Darker skin needs more sun to form vitamin D because the dark pigment blocks sunlight in exactly the same way as clothes and high sun protection factor sun cream. This means it provides more protection against the harmful rays of the sun.

In the UK, the sun’s UV radiation is strongest from early April to the end of September, especially in June and July, and the body can usually absorb large amounts of vitamin D very quickly. During this time of year, exposing the skin for 15-30 minutes a few days a week is usually enough to get the vitamin D you need.

From October to March, the sunlight is often too weak for you to absorb enough vitamin D and you have to rely on the vitamin D you’ve stored. Over time, your levels of vitamin D will drop, typically reaching their lowest levels as early as January or February. This is when it becomes especially important to compensate with a diet rich in vitamin D or supplements.

Sources of vitamin D

  • The sun – when your skin is exposed to the sun's UV radiation, it converts the sun’s rays to vitamin D, which is then stored in your body
  • Artificial UVB radiation – the radiation from certain solariums or tanning beds
  • Animal foods – fatty fish like salmon and herring, fish eggs and meat
  • Plant foods – mushrooms and vegetables (often lower levels of vitamin D than animal sources)
  • Vitamin D-enriched foods – dairy products, margarine, as well as some oat and soya drinks
  • Dietary supplements – vitamin D can be taken as a supplement in various strengths and forms (powder or tablet)

Symptoms of vitamin D deficiency

Vitamin D deficiency in adults is a condition that develops over an extended period of time. There are a wide range of possible symptoms that may not have an obvious connection to vitamin D – they can include general tiredness, depression, weakness, or muscular weakness.

Examples of other symptoms:

  • Muscular cramps and pains
  • Difficulty walking
  • Difficulty climbing stairs

In more serious cases, long-term and severe vitamin D deficiency can lead to soft or brittle bones. The medical term for bone softness is osteomalacia, while brittle bones are caused by osteoporosis.

Vitamin D deficiency in children

Children are particularly vulnerable to vitamin D deficiency. Their bones need vitamin D to develop properly, otherwise they can become soft or deformed. Vitamin D deficiency in children can lead to bone deformities like rickets, having a sunken chest or deformed pelvis. In infants, the fontanelles – the soft spots between the bone plates of the skull, can take longer to close and the head may become enlarged. Children can take a daily supplement throughout the year to avoid deficiency.

Causes of vitamin D deficiency

Low levels of vitamin D or vitamin D deficiency may be a result of too little sun exposure or too little vitamin D in your diet. Certain medical conditions can also lead to vitamin D deficiency. The production of vitamin D in the skin also drops with age. Here are some of the most common causes.

  • Low vitamin D production in the skin – your skin may not produce enough vitamin D if you’re older, have dark skin, wear heavy sun protection and full-coverage clothing, or there isn’t enough sunlight around you
  • Low absorption of fat in the gut – coeliac disease, gastrointestinal disease, cystic fibrosis or gastric bypass-operation can reduce the amount of vitamin D that your gut absorbs
  • Obesity – vitamin D may be stored in fatty tissue instead of circulating around the body
  • Breastfeeding with no vitamin D supplement – breastmilk doesn’t naturally contain enough vitamin D
  • Pregnancy – the body needs more vitamin D during pregnancy
  • Certain diseases – for example chronic kidney failure, severe liver disease and hyperthyreosis
  • Medication – certain medicines can impact your vitamin D levels

High-risk groups

Studies show that around 1 billion people globally have a vitamin D deficiency or low levels of vitamin D. The elderly are most at risk, as well as the following groups.

  • If you are under-exposed to the sun
  • People with darker skin
  • Premature babies
  • Children who don’t receive a vitamin D supplement
  • Pregnant women who don’t have a vitamin D-rich diet
  • If you have an unbalanced diet
  • If you are overweight

Treatment for vitamin D deficiency

Diagnosing vitamin D deficiency usually requires a blood test. A doctor might also check your levels of other vitamins or hormones linked to vitamin D. If you have a vitamin D deficiency, a doctor may prescribe vitamin D supplements – and the amount will depend on your symptoms and level of deficiency.

Vitamin D must always be taken as a daily supplement for children up to the age of at least 2.

What can I do to prevent vitamin D deficiency?

It’s always best to choose foods that are rich in vitamin D, and aim to expose your skin to 15-30 minutes of sunlight for a few days each week (during the sunny parts of the year). A short amount of time in the sun is sufficient – always take care to protect yourself from sunburn.

If you’re in a high-risk group for vitamin D deficiency or have low levels in the winter, you’ll need vitamin D as a dietary supplement. A doctor can give you advice on what’s best for you.

Recommended daily intake of vitamin D:

  • Children up to 2 years old – 10 micrograms
  • Children and adults under the age of 75 – 10 micrograms
  • Adults over the age of 75 – 20 micrograms

Can I have too much vitamin D?

The risk of getting side effects from too much vitamin D is low, but in some cases, taking large amounts of vitamin D can cause vitamin D poisoning. You can’t absorb dangerous amounts through your diet or sunlight, but taking an excess of vitamin D supplements could result in an overdose of vitamin D.

When to speak to a doctor

It’s a good idea to talk to a doctor if you’re experiencing related symptoms, like feeling constantly tired and weak. A doctor will assess your symptoms and can provide necessary prescriptions or referrals if they identify a vitamin D deficiency.

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