Vitamin D is a fat-soluble vitamin, found naturally in very few foods. It is added to other foods such as cereals and is available as a dietary supplement. We all need vitamin D in order to grow and thrive.

Vitamin D is an essential nutrient, produced naturally in the skin after exposure to direct sunlight. When this vitamin is at an insufficient level, bones are weakened and overall health declines. From infancy, through childhood and all the years of adulthood, vitamin D has a crucial role in maintaining our health and appearance. It is therefore important to ensure the body has all it needs.

For Vitamin D production, skin must be exposed regularly to direct sunlight to achieve the necessary amounts of Vit D. This means certain people are at risk for vitamin D deficiency, such as night shift workers and the chronically ill or bedridden. African Americans also need to monitor their vitamin D, since darker skin absorbs less sunlight. The sunlight must be direct, so sitting by a window will not be enough. The UV rays needed to start the process of vitamin D production cannot penetrate glass. It is recommended that people expose their skin to direct sunlight as often as possible, for twenty minutes per day. This can be difficult at times for all people, but particularly the elderly. This puts the elderly in the high risk group also.

Another reason for vitamin D deficiency can be that certain medications deplete it from the body.

Milk, assumed by many to be a prime source of vitamin D, may actually contain very little of it, or none at all, however it is still useful as it provides calcium which Vitamin D can then help the body to absorb. In addition, the body needs some fat in the diet for Vit D absorption, which milk can provide. This is why low-fat diets also put people at risk of deficiency.

Vitamin D is not just a vitamin, it is also a hormone. It assists the gastrointestinal tract to absorb calcium. In fact, vitamin D is so essential for calcium absorption that nearly all calcium supplements now contain it as a supplement. In addition to working with calcium, the vitamin D as a hormone causes other minerals in the body, such as magnesium, zinc and iron, to concentrate on bone production. So vitamin D is absolutely essential for bone health.

Vitamin D exists in several forms, the two main ones being vitamin D2 (ergocalciferol), and vitamin D3 (cholecalciferol). These are known collectively as calciferol. They are secosteroids, which are similar in structure to steroids but the second carbon ring is open. Vit D2 is produced by phytoplankton, invertebrates, and fungi in the presence of UV rays. Vit D3 is made by humans in the skin, again in response to UV rays.

Whatever the form of Vitamin D, it is biologically inert (i.e. can't be used by the body) and therefore has to undergo two hydroxylations (gaining an -OH group) to become active. The first occurs in the liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol (meaning two alcohol OH groups). The second occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol (meaning three alcohol OH groups).

The most common result of vitamin D deficiency is bone loss and skeletal problems. Rickets, once a common disease among the poor, was eradicated completely when physicians learned that regular sun exposure promotes production of vitamin D, which in turn promotes healthy bone growth. When sun exposure is not possible, supplements must be given. The most prevalent health risk today that is associated with low levels of vitamin D, is osteoporosis. Osteoporosis is a condition that thins the bones causing them to become weak, brittle, and prone to breaking. Along with aging, particularly in women, osteoporosis is responsible for as many as 70 percent of broken hips that occur in falls, and even spontaneously. In the elderly, a broken hip often marks the beginning of a decline that leads death.

Some other health problems often seen in correlation with low levels of vitamin D are psoriasis, Crohn’s disease and multiple sclerosis (MS). Healthy levels of Vitamin D improve blood pressure, osteoarthritis, and even help fight against cancer. Vitamin D has been proven to reduce tumors. In laboratory experiments, vitamin D supplementation caused a reduction of 50% in cancerous growths.

Ensuring that vitamin D levels are sufficient in the body is essential for all people. Not only is it essential for bone health, but also skin health and general well being. Vitamin D directs essential minerals to concentrate where they are needed. By exposing skin to the sunshine and by supplementing, vitamin D is made available for a lifetime, keeping bones and body strong and healthy.

Dosage Vitamin D content is stated in either micrograms (µg or mcg) of cholecalciferol or International Units (IU). One IU equals 0.025 µg cholecalciferol, therefore to convert IUs of Vit D into µg, multiply the number of IUs by 0.025 and that will give you the number of µg. To convert µg to IUs, multiply the number of µg by 40 and that will give you the number of IUs.

The recommended daily amount (RDA) for most adults and children is 5µg (200 IUs). If you're between 51 - 70 years the RDA is 10µg (400 IUs). Over 70 the RDA is 15µg (600 IUs).

Vitamin D is tolerated well in dosages over this. The LOWEST tolerable Upper Limit (maximum amount that can be tolerated without harm) is 25 micrograms(µg) per day (1000 IU) for infants under 12 months. For those aged between 9 - 71+ years (including pregnant or lactating women) the tolerable upper limit is 100µg per day (4000 IUs).

A daily supplement of between 10µg (400 IUs) and 20µg (800 IUs) should therefore be suitable for most people.