Vitamin D
Vitamin D is the one vitamin that is produced by the body itself and so
doesn’t need to be consumed. It is instead produced by sunlight hitting the
skin. Although exposing your skin to intense sunlight for long periods has known
health problems such as sunburn and eventual skin cancer, some exposure is
needed to produce your recommended daily allowance of vitamin D. The amount skin
exposure and length of time necessary to produce enough vitamin D to fulfill
your recommended daily allowance is very small amounting to just a few minutes
per day and doesn’t put you skin under any risk from ultra violet radiation.
The main and most vital role of vitamin D in the body is the control of the absorption of calcium from the food we eat (mainly dairy products). Calcium’s main function is to help build and strengthen bones and teeth but it also has many other functions including aiding the sending of messages along neurons and helping muscles, including the heart muscles to contract. Vitamin D ensures that there is always enough calcium in the blood to fulfill these functions when required. The other functions of vitamin D in the body relate to the aiding the immune system and it may play a part in reducing the risk of contracting certain cancers, particularly colon cancer.
A variant of vitamin D called cholecalciferol is also formed under the skin alongside ordinary vitamin D. Cholecalciferol or D3 is formed when ultraviolet spectrum sunlight reacts with a type of cholesterol found naturally under the skin. This D3 or cholecalciferol is then taken to and converted by the liver into a more active form before being swiftly transported to where it is needed most urgently. Some vitamin D remains inside the liver and kidneys where it aids in the re-absorption of calcium from the blood. The rest is dispersed throughout the body’s bones where it helps them to retain and absorb calcium as necessary. Some goes to the intestines to absorb fresh calcium from food.
Even though the body produces the vast majority of vitamin D it requires through the skins exposure to sunlight, there are a few foods that contain some vitamin D naturally. This is a third type of vitamin D known as ergocalciferol or vitamin D2. Ergocalciferol works in exactly the same way as other D vitamins and is used widely to create vitamin D supplements.