Vitamins are vital in human nutrition but for the most part cannot be manufactured by your body. Therefore, you have to get vitamins from a healthy diet. Vitamins actually work as essential co-factors for properly regulating your body's metabolic reactions and biochemical processes.

When your diet is deficient in vitamins, many biological functions are disrupted, resulting in suboptimal health as well as a wide variety of disease conditions specifically related to nutrient imbalances. Vitamins are classified as fat soluble and water soluble. This means they are dissolved and stored in either the fatty tissues of your body or the water tissues.

Water soluble vitamins, vitamin C and B complexes, are easily excreted by your body through the urine. They cannot be stored in your body for future use and require daily intake for maximal health.

Fat Soluble Vitamins

Fat-soluble vitamins are stored in the reserves of fatty body tissues and can therefore be drawn upon when they are not obtained daily from the diet. This makes them very available for a period of time even if your diet becomes extremely deficient. Ultimately, however, the reserve of fat soluble vitamins can be depleted and will need to be replenished from your diet. Because these fat soluble vitamins are not easily excreted by your body, excessive intake of fat-soluble vitamins can cause toxicity. The fat-soluble vitamins are vitamins A, D, E, and K.

Vitamin A

Vitamin A was the first vitamin to be discovered and officially named, hence its letter A. Vitamin A is actually a group of nutrients that include retinol, retinal, and the carotenoids. Retinol and retinal are both known as preformed vitamin A and are found in a variety of animal foods, especially liver. Butter, cream, egg yolk, fish oils, and whole and fortified nonfat milk are all good sources of preformed vitamin A.

Carotenoids refer to over 500 substances which naturally occur in fruits and vegetables. Some 50 carotenoids act as precursors to vitamin A, with beta-carotene being the most well-known and most prevalent in foods. Lycopene is another well-studied carotenoid now known for its important role in healing. It is found in abundant levels in tomatoes.

The best food sources of carotenoids are yellow and dark green vegetables, orange fruits, tomatoes, watermelons, and cherries. Orange fruits and green, leafy, and yellow vegetables are all loaded with various precursor carotenoids, particularly beta-carotene, which the body converts to vitamin A.

Vitamin A is important for a wide variety of functions in your body. It supports eyesight, healthy teeth and skin, bone growth, cell differentiation, and tissue repair. Vitamin A also plays an important role in maintaining proper function of the cornea, lungs, mucus membranes, the lining of the gastrointestinal tract, and the bladder and urinary tract. It also acts as an antioxidant which in turn helps prevent inflammation and regulates infectious disease. In addition, it is needed for the production of various anti-tumor compounds in your body, making it a powerful nutrient in the prevention of cancer.

Vitamin A can be depleted in the body by stress and illness as well as alcohol consumption. Alcohol can interfere with vitamin A absorption. A common symptom of vitamin A deficiency is night blindness but can also include sub-optimum bone and tooth formation, eye inflammation, impaired immune response and even weight loss. An unusual condition, keratinosis (hardened pigmented deposits around hair follicles on the body's upper and lower extremities) is another symptom of vitamin A deficiency.