Vitamin D

Adam Mason-Smith

ID:11346129

Vitamin D

Abstract

For years vitamins and minerals have been improving peoples health and lives and vitamin D is no exception. Noted mostly for it's bone strengthening qualities as well as reducing the chance of many common ailments and cancers. These facts often see vitamin D introduced into many commercial foods. But vitamin D doesn't need to be ingested like other vitamins, it's biosynthesis makes it truly special. A little sunshine each day and human skin will create all the vitamin D necessary for optimum health. Even so, for years people have been supplementing their diets with fish and other seafoods, well known foods high in vitamin D. Commonly used for sufferers of bone malforming diseases ,like osteoporosis, vitamin D works in the body to activate enzymes responsible for absorbing minerals like calcium and phosphorous into bones. Like all vitamins there are recommended daily intakes and vitamin D is one of the few vitamins that you can take too much of. Overdosed vitamin D can't pass out of the body as a liquid so buildups of it can be harmful.

Introduction

Before age modern science allowed us to understand how our bodies function, the likes of the ancient Egyptians and Hippocrates were noted for the use of liver for health benefits. Centuries on, in 1915, the answer as to why it was an efficient prescription for night blindness was discovered, the health benefits of food was due to organic molecules such as the then newly discovered vitamin A. (Dr. R.C. Atkins, 2002) 96 Years on and many other vitamins, as well as minerals have been discovered, all with the unique health benefits they possess. Among these is perhaps one of the most unique groups of molecules, due to the biosynthesis process and that it's considered a hormone in its active form; Vitamin D or Calciferol.

Vitamin D Synthesis

Like the well-known B vitamins, there are a collection of molecules, or metabolites, in the Vitamin D group, although only a few occur naturally in humans. Vitamin D3, also known as cholecalciferol, is the form synthesized in the skin of living organisms. Due to this, animals have no real dietary requirements in regards to vitamin D as the skin of an organism can produce all that is necessary, if it gets enough sunlight. Under direct UVB radiation, of 290-315 nm, (J. Mann & S. Truswell, 2007) a minor cholesterol companion in the skin known as 7-Dehydrocholesterol will undergo a chemical reaction to form vitamin D3.

7-Dehdrocholesterol Previtamin D3 Vitamin D3

( http://commons.wikimedia.org/wiki/)

Under the short-wavelength UVB light, the benzene ring of the sterol breaks at the ninth carbon to form previtamin D, a secosterol. This is a rapid metamorphosis. The second stage of the reaction takes place at a slower pace and in warmth, where the secosterol undergoes a more complex rearrangement to form vitamin D3. In this reaction the double bond between carbons six and seven breaks and they form new double bonds on their respective other neighbouring carbon.

Because vitamin D3 is produced in only a single organ, the skin, and transported to other organs through the blood, it is technically considered a hormone. The molecule is not truly active however, until it passes through the liver and kidneys via the blood and has been chemically hydroxylated twice. Transported to the liver by vitamin D specific binding proteins, α2-glodulin, Vitamin D3 is hydroxylated at the 25th carbon in the liver microsomes to form 25 (OH)D3. When transported to the kidneys, the molecule undergoes one further hydroxylation at the first carbon, producing 1,25 (OH)D3. This chemical change is performed by 1α-hydroxylase, an enzyme found in the kidneys. (J. Mann & S. Truswell, 2007)

Vitamin D3 25 (OH)D3 1,25 (OH)D3

(http://commons.wikimedia.org/wiki/)

Function of Vitamin D

Like most vitamins, Vitamin D functions as a coenzyme, ensuring enzymes in the body perform the chemical reactions necessary for life. Once 1,25 (OH)D3 has been formed in the kidneys it binds to specific receptor proteins in cell nuclei. The receptor then activates the gene responsible for synthesizing calbindin, the calcium transport protein. These proteins synthesize in the epithelial cells of the small intestine and transport ingested calcium through the bloodstream to high calcium phosphate areas such as bones and teeth. Vitamin D3 can also increase the absorption of other minerals such as magnesium, zinc, iron and phosphorous and their mobilization from around the body towards the bones. (H. Walji, 1996)

The beneficial effects of vitamin D in the body are clear, it helps maintain and grow a healthy skeletal structure. And with vitamin D being such an important nutritional necessity for bones, a lack of it would surely pose a serious health deficiency. Rickets is a well-known bone deforming condition common amongst wealthy children of the middle ages, who would normally be assumed to be healthier than other, less wealthy children. Growing up in large estates with limited access to outdoor activity, these children lacked the UV sunlight to maintain a healthy level of vitamin D. Bone deficiencies in adults such as osteoporosis are also associated to depleted levels of vitamin D.

Vitamin D is a fat-soluble vitamin so, unlike water-soluble vitamins, cannot be regularly excreted through urine and stay in the body for a longer time. Due to this, highly elevated levels of vitamin D in the body can have toxic effects on the body. The optimum daily intake for vitamin D in grown men and women is up to 1000 IU (International Units for vitamin dosage) per day and higher levels have shown to lead to hypervitaminosis, a vitamin overdose condition. (Dr. S Lieberman & N. Bruning, 2007) Nausea, diarrhea, headaches, loss of appetite, restlessness and fatigue are common signs of this