What is Vitamin D (Calciferol) ?
Vitamin D is a fat-soluble vitamin which is stored in the body and is unique when compared to the other vitamins. It is a steroid hormone which is produced from cholesterol when the skin is exposed to the sun.
The two main dietary forms of vitamin D are:
- Vitamin D3 ( or cholecalciferol). This is found in some animal foods such as fatty fish and egg yolks.
- Vitamin D2 (or ergocalciferol). This is found in some plants, mushrooms and yeasts.
Vitamin D3 (cholecalciferol) is twice as effective at increasing the blood levels of vitamin D than vitamin D2 (ergocalciferol).
Health Benefits of Vitamin D
Vitamin D has several health benefits including:
- Helps keep bone and teeth healthy. Vitamin D helps to regulate the amount of calcium and phosphate in the body. These are the main nutrients necessary for healthy bones. Vitamin D therefore strengthens the bones and prevents osteoporosis and osteomalacia.
- Boosts the immune system. Vitamin D strengthens the immune system making it more effective in fighting infections, such as the flu and other bacterial and viral infections.
- Helps keep muscles strong and healthy. The muscles need vitamin D to move and studies have shown that high levels of vitamin D may help to optimise muscle strength. In addition, the nerves need vitamin D for them to be able to carry messages between the brain and the body.
- May help reduce the risk of developing type I diabetes.
- May help reduce the risk of some cancers, such as breast and colon cancer.
Dietary Sources of Vitamin D
Only a few foods naturally contain vitamin D. Dietary sources of vitamin D include:
- Fatty fish, such as trout, salmon, tuna, and mackerel, and fish liver oils are the best natural sources of vitamin D.
- Beef liver, red meat and egg yolks contain small amounts of vitamin D.
- Mushrooms contain small amounts of vitamin D. Some mushrooms are exposed to ultraviolet light to increase their vitamin D content.
- In some countries milk is fortified with vitamin D. Many plant-based alternatives such as soy milk, almond milk and oat milk are also fortified. Foods made from milk, such as cheese and ice cream, are not usually fortified.
- Vitamin D is added to many breakfast cereals and to some brands of orange juice, yogurt, margarine, and other food products.
Vitamin D can also be produced from your skin when it is exposed to ultraviolet B (UVB) light from the sun. A large part of your body needs to be exposed to the sun because if only your face and hands are exposed much less vitamin D will be produced.
How much vitamin D do I need?
The only way to know if you are deficient in vitamin D is by having your blood levels measured.
The amount of vitamin D is usually expressed as micrograms (mcg or μg) or as International Units (IU). 1 mcg of vitamin D is equal to 40 IU. Therefore 10 micrograms of vitamin D is equal to 400 IU.
The Recommended Daily Amount (RDA) for vitamin D is 400 IU (10 mcg)
Signs of Deficiency
Vitamin D deficiency results in diseases which are characterised by soft, poorly formed bones. In children this results in rickets and in adults it causes osteomalacia. Both conditions are rare in the West except in the elderly, who are less likely to get sufficient exposure to sunlight. This usually leads to osteoporosis
What happens if I take too much vitamin D?
Of all the vitamins, vitamin D has the most potential to be toxic. Taking too many vitamin D supplements over a long period of time (more than 1,000 IU daily) can cause too much calcium to build up in the body (hypercalcaemia). This can weaken the bones and damage the kidneys and the heart.
If you take vitamin D supplements, 10mcg (400 IU) daily will be enough for most people.
Do not take more than 100 micrograms (4,000 IU) of vitamin D a day as it could be harmful. This applies to adults (including pregnant and breastfeeding women and the elderly) and children aged 11 to 17 years. Some people may have medical conditions which may mean that they are unable to safely take as much. If in doubt, consult your doctor.
If your doctor has recommended you take a different amount of vitamin D, you should follow their advice.
You cannot overdose on vitamin D obtained from exposure to sunlight. Remember to cover up or protect your skin if you’re out in the sun for long periods to reduce the risk of skin damage and skin cancer.
Possible Interactions
Corticosteroids can increase the body’s demand for vitamin D.
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