What is vitamin D?

Vitamins are a group of chemicals that are needed by the body for good health. Vitamin D is a fat-soluble vitamin. The fact that it dissolves in fat is important, because it means the body can store it for future use. Unlike other vitamins, we do not need to get vitamin D from the food that we eat. This is a good thing because most foods contain very little vitamin D naturally. Foods that contain vitamin D include:

• Oily fish (such as sardines, pilchards, herring, trout, tuna, salmon and mackerel).
• Egg yolk.
• Fortified foods (this means they have vitamin D added to them) such as margarine, some cereals, infant formula milk.

Who gets vitamin D deficiency?

Vitamin D deficiency means that there is not enough vitamin D in the body. Broadly speaking, this can occur in three situations:

1. The body has an increased need for vitamin D.
2. The body is unable to make enough vitamin D.
3. Not enough vitamin D is being taken in the diet.

Increased need for vitamin D

Growing children, pregnant women, and breast-feeding women need extra vitamin D because it is required for growth. So, vitamin D deficiency is more likely to develop in the following groups of people:

• Pregnant or breast-feeding women. Vitamin D deficiency is even more likely to develop in women who have had several babies with short gaps between pregnancies. This is because the body's stores of vitamin D get used up, and there is little time for them to be built up before another pregnancy.
• Breast-fed babies whose mothers are lacking in vitamin D, or with prolonged breast-feeding, as there is little vitamin D in breast milk. (Note: there are significant advantages to breast-feeding; you should not stop breast-feeding due to concern about vitamin D levels - your baby can simply have vitamin D supplements as drops by mouth.)

Situations where the body is unable to make enough vitamin D

People who get very little sunlight on their skin are also at risk of vitamin D deficiency. This is more of a problem in the most northern parts of the world where there is less sun. In particular:

• People who stay inside a lot. For example, those in hospital for a long time, or housebound people.
• People who cover up a lot of their body when outside. For example, wearing veils such as the niqab or burqa.
• People with pigmented (dark coloured) skins. This includes black and Asian people. Caucasian (white) people are less at risk.
• Strict sunscreen use can potentially lead to vitamin D deficiency, particularly if high sun protection factor (SPF) creams (factor 15 or above) are used. Nevertheless, children especially should always be protected from the harmful effect of the sun's rays and should never be allowed to burn or be exposed to the strongest midday sun.
• Elderly people have thinner skin than younger people and so are unable to produce as much vitamin D. This leaves older people more at risk of vitamin D deficiency.
• Some medical conditions can affect the way the body handles vitamin D. People with Crohn's disease, coeliac disease, and some types of liver and kidney disease, are all at risk of vitamin D deficiency.
• Vitamin D deficiency can also occur in people taking certain medicines - examples include: carbamazepine, phenytoin, primidone, barbiturates and some anti-HIV medicines.

Not enough dietary 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.

How common is vitamin D deficiency?

It is very common. A recent survey in the UK showed that more than half of the adult population in the UK has insufficient levels of vitamin D. In the winter and spring about 1 in 6 people has a severe deficiency. It is estimated that about 9 in 10 adults of South Asian origin may be vitamin D-deficient. Most affected people either don't have any symptoms, or have vague aches and pains, and are unaware of the problem.

What are the symptoms of vitamin D deficiency?

Many people have no symptoms, or only vague ones such as tiredness or general aches. Because symptoms of vitamin D deficiency are often very nonspecific or vague, the problem is often missed. The diagnosis is more easily reached in severe deficiencies with some of the classical (typical) symptoms and bone deformities.

Symptoms in babies and children

• Babies with severe vitamin D deficiency can get muscle spasms (cramps), seizures and breathing difficulties. These problems are related to consequent low levels of calcium.
• Children with severe deficiency may have soft skull or leg bones. Their legs may look curved (bow-legged). This condition is known as rickets. (See separate leaflet called 'Rickets' for more information.)
• 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.
• Irritability in children can be due to vitamin D deficiency.
• Children with vitamin D deficiency are more prone to infections. Respiratory (breathing) symptoms can occur In severe cases. Breathing can be affected because of weak chest muscles and a soft ribcage.
• Rarely, an extremely low vitamin D level can cause weakness of the heart muscle (cardiomyopathy).

Symptoms in adults

• General vague aches and pains are the common symptoms.
• In more severe deficiency, there may be more severe pain and also weakness. This may lead to difficulty standing up or climbing stairs, or can lead to the person walking with a 'waddling' pattern. This is known as osteomalacia. (See separate leaflet called 'Osteomalacia' for more information.)
• Bone pains may develop and are typically felt in the ribs, hips, pelvis, thighs and feet.

How is vitamin D deficiency diagnosed?

It may be suspected from your medical history, symptoms, or lifestyle. A simple blood test for vitamin D level can make the diagnosis. Blood tests for calcium and phosphate levels and liver function may also show changes linked to a low level of vitamin D. Sometimes, a wrist X-ray is done for a child. This can assess how severe the problem is by looking for changes in the wrist bones.

What is the treatment for vitamin D deficiency?

The treatment is to take vitamin D supplements. This is a form of vitamin D called ergocalciferol or calciferol. Vitamin D can be given as an injection or as a medicine (liquid or tablets). Your doctor will discuss the dose, and best treatment schedule, depending on your situation, age, severity of the deficiency, etc. Briefly, one of the following may be advised

Injection

A single small injection of vitamin D will last for about six months. This is a very effective and convenient treatment. It is useful for people who do not like taking medicines by mouth, or who are likely to forget to take their tablets.

High-dose tablets or liquids

There are different strengths available and a dose may be taken either daily, weekly or monthly. This will depend on your situation and on which particular treatment guideline your doctor is using. Always check with your doctor that you understand the instructions - with high doses of vitamin D it is important to take the medicine correctly. The advantage of the higher-dose treatment is that the deficiency improves quickly - important in growing children.

Standard-dose tablets, powders or liquids

These need to be taken every day for about 12 months in order that the body can catch up on the missing vitamin D. This is a rather slow method of replacing vitamin D, but is suitable if the deficiency is mild, or for prevention. A disadvantage is that all these preparations contain either calcium or other vitamins, giving them a strong taste which some people dislike.

Maintenance therapy after deficiency has been treated

After vitamin D deficiency has been treated, the body's stores of vitamin D have been replenished. After this, maintenance treatment is often needed long-term, to prevent further deficiency in the future. This is because it is unlikely that any risk factor for vitamin D deficiency in the first place, will have completely resolved. The dose needed for maintenance may be lower than that needed to treat the deficiency.

Preventing vitamin D deficiency

Various groups of people (detailed earlier) are prone to develop vitamin D deficiency. Therefore, in summary, the following groups of people are advised to take vitamin D supplements routinely.

• All pregnant and breast-feeding women.
• Breast-fed babies. (Bottle-fed babies do not need vitamin D supplements as formula milk is fortified with vitamin D.)
• Young children up to the age of five years.
• All older people aged 65 and over.
• People whose skin is not exposed to much sun. For example, people who cover their skin for cultural reasons, people who are housebound, etc.
• People who have darker skin. (For a given amount of sun exposure, people with darker skin produce less vitamin D than people with lighter skin.)

A doctor may also advise routine vitamin D supplements for people with certain gut, kidney or liver diseases, and people prescribed certain medicines.

The dose advised varies depending on your circumstances, age, etc. Your doctor, nurse or midwife will advise on the dose. Note: pregnant women can get free prescriptions and vitamins.

Cautions when taking vitamin D supplements

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. Specialist advice may be needed.
• Vitamin D should not be taken by people who have high calcium levels or certain types of cancer.
• You may need more than the usual dose if taking certain medicines which interfere with vitamin D. These include: carbamazepine, phenytoin, primidone, barbiturates and some medicines for the treatment of HIV infection.

Multivitamins are not suitable for long-term high-dose treatment because the vitamin A they also contain can be harmful in large amounts.

Are there any side-effects from vitamin D supplements?

It is very unusual to get side effects from vitamin D if taken in the prescribed dose. However, very high doses can raise calcium levels in the blood. This would cause symptoms such as thirst, passing a lot of urine, nausea or vomiting, dizziness and headaches. If you have these symptoms, you should see your GP promptly, so that your calcium level can be checked with a blood test.

Some guidelines advise that people taking high vitamin D doses should have their calcium levels checked during the first few weeks. In practice, this is not usually done unless you have symptoms of high calcium as described above.

Prognosis (outlook) in vitamin D deficiency?

The outlook for vitamin D deficiency is usually excellent. Both the vitamin levels and the symptoms generally respond well to treatment. However, it can take time (months) for bones to recover and symptoms such as pain to get better or improve.

The complications of severe deficiency have already been mentioned. Rickets can occur in children, and osteomalacia in adults. These diseases affect the strength and appearance of bones, and can lead to permanent bone deformities if untreated or if treatment is very delayed.

Vitamin D is increasingly being linked to other diseases and illnesses. In recent years there have been associations with conditions such as cancer, heart disease, infectious disorders, autoimmune disease and diabetes. This does not mean that all people with vitamin D deficiency will get these problems. Nor does it mean that if you have one of these illnesses, a vitamin D deficiency is the cause. In these cases, vitamin D is thought to be just one factor.

Follow-up

Most people who are treated for vitamin D deficiency will need to be reviewed a few weeks or months after starting treatment - depending on how severe their symptoms are. A further review after one year is advised.

A useful source of information

Healthy Start scheme

Web: www.healthystart.nhs.uk
A government-run scheme. With Healthy Start, you can get free vouchers every week, which you swap for milk, fresh fruit, fresh vegetables and infant formula milk. You can also get free vitamins. You could qualify if you receive benefits (Jobseeker's Allowance, Income Support or receive Child Tax Credit) or if you are pregnant and aged under 18.

References

• Pearce SH, Cheetham TD; Diagnosis and management of vitamin D deficiency. BMJ. 2010 Jan 11;340:b5664. doi: 10.1136/bmj.b5664.
• Drug and Therapeutics Bulletin; Primary vitamin D deficiency in children. February 2006 44: 12-16; (Requires a subscription)
• Drug and Therapeutics Bulletin, April 2006 44: 25-29. Primary vitamin D deficiency in adults. (Requires a subscription)
• Holick MF; Vitamin D deficiency. N Engl J Med. 2007 Jul 19;357(3):266-81.
• Update on Vitamin D, Scientific Advisory Committee on Nutrition, February 2007