Vitamin D is often called the sunshine vitamin. This is because it is produced when the UV rays from the Sun react with a cholesterol related chemical in the skin. Over a period of time this chemical is converted into vitamin D by the liver and kidneys.

As little as 15 minutes of Sun twice a week to your arms, hands, and face will allow enough vitamin D to be generated to meet the average human requirements. Vitamin D can also be absorbed from digested food. Sources include fish-liver oils, egg yolk, and fortified milk. Vitamin D is one of the few vitamins, which can be stored. It is soluble in fat which makes the Vitamin D produced in the summer last most people all winter.

However Vitamin D formation will be halted by window glass, sunblockers, sunscreens (with an SPF over 8), smog, and clothing. The formed Vitamin D is stored in the liver.

Vitamin D is very important as it performs various functions in our body such as:

1. It regulates the absorption and metabolism of calcium and phosphorus resulting in strong bones and teeth.
2. It is necessary for the proper absorption of calcium and phosphorus from the intestine.
3. It helps in maintaining normal calcium levels.
4. Vitamin D stimulates calcium and phosphorus to enter the bloodstream. This process strengthens bones and helps to maintain healthy nerves and muscles. Most calcium supplements are enriched with Vitamin D because it helps to absorb calcium and promotes its circulation throughout the body.

Lack of Vitamin D can have the following effects:

1. Rickets in children which is characterized by soft and easily bending bones, bowed legs, and knock knees along with stunted growth and deformed chests.
2. In adults its deficiency causes Osteomalacia in which bones lose their strength and tend to fracture easily and hurt a lot.
3. A lack of Vitamin D results in muscle cramps and twitching.

If the Vitamin D level drops considerably, so do the concentrations of calcium and phosphorus in the blood. When calcium and phosphorus are low, the body will strip calcium and phosphorus from the bones to correct the imbalance making bones very weak.

Thus we can see that Vitamin D is very essential for good health. The Sun thus acts as a true "friend" by helping us manufacture this truly vital vitamin.