Vitamin D is one of the few vitamins our body needs that can be produced independently of our diet. This fat-soluble vitamin is unique in humans because it functions as a prohormone, a precursor to the ordinary hormone, and is synthesized when our skin is exposed to the sun.
It is synthesized in the kidneys in the form of calcitriol before it is released into the body as a hormone. It regulates the concentration of calcium and phosphate in the blood stream, helping to promote healthy growth and remodeling in our bones.
The regular intake or production of Vitamin D in our bodies can help to prevent rickets in children and the onset of osteomalacia in adults. Vitamin D, especially when combined with calcium, helps to maintain healthy bones and can also reduce the risk of osteoporosis later in life.
While it is commonly known that Vitamin D is good for the health of our bones, many people do not know that it also affects the function of the neuromuscular and immune systems, inflammation and cell growth. Vitamin D also partly modulates the genes in the body that regulate cell proliferation, differentiation and apoptosis .
The recommended dietary intake, recommended by the Food and Nutrition board at the Institute of Medicine of the National Academies, is about 15-20mcg in a healthy adult for optimal bone and overall health .
Even though getting regular sunlight is the simplest way to top up Vitamin D levels, many people don’t get sufficient sun, particularly due to our colder climate–and especially during the winter. Fortunately there are plenty of food sources out there that can help support our Vitamin D intake.
In some countries, it is not uncommon to come across food that has been artificially fortified with Vitamin D . But the regular consumption of fatty fish, such as catfish, salmon, mackerel, sardines, eel and tuna, can help to naturally get enough Vitamin D in our diet. Other food sources are also rich in Vitamin D, such as: whole eggs, beef liver, fish liver oils (including cod liver oil), mushrooms and yeast that have been grown under UV light.
It is important to maintain a healthy balanced diet rich in Vitamin D and to get enough sunlight when the weather is nice enough to do so. Vitamin D is important for a healthy skeletal system, immune system , may reduce the risk against cancer  and may even reduce the overall mortality risks from any cause .
 Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
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