Vitamins synthesis by intestinal bacteria

Although, by definition, vitamins required by man cannot be synthesized within the tissues, it is important to note that bacteria within the gut can synthesis many of the vitamins required by man. The human intestinal bacteria can synthesize vitamin K, a member of the naphtoquinone family.

Vitamin K2 also called menaquinone also is a product of metabolism of most bacteria including the normal intestinal bacteria of most higher animal species. The vitamin K bacterial reactions occur, in part, in the ileum, where the menaquinone is absorbed.

Among bacteria involve in synthesizing vitamin K are: Bacteroides spp., Eg. Lenta, Propionibacterium spp., Veillonella spp., staphylococci, enterococci enterobacteria.

Most of the vitamin B12 (cyanocobalamin) required by humans comes indirectly from the meat and milk of ruminants. The synthesis of B12 is ruminant is exclusively bacterial origin. It appears most of the bacterially formed B12 I human occurs in the large bowel. It was demonstrated that E. coli, Bifidobacterium spp., Veillonella spp., Fusobacterium spp., Eurobacterium spp., and Clostridium spp., among the bacteria that synthesized B12 in the small intestine.

Folic acid and thiamine B complex vitamins are also synthesized by bacteria in the intestinal tract. Other vitamins synthesized by intestinal bacteria are:
*Biotin
*Folic acid (B2)
*Pantothenic acid (B5)
*Niacin (B3)
*(Pyridoxine) B6
Vitamins synthesis by intestinal bacteria

Synthesis of vitamin D in the skin

The human body also is able to synthesize this vitamin from components of the skin through exposure to ultraviolet or sunlight. Most of the world’s population relies on natural exposure to sunlight to maintain adequate vitamin D nutrition.

To get all vitamins D is to go outside. That’s because vitamin D is made when the sun shines on the human skin.

In the skin, 7-dehydrocholesterol in the epidermis and dermis changes conformation ultraviolet B (UVB) radiation in the wavelength range of 280-315 nm passes through these skin layers to form pre-vitamin D3.

Subsequent enzymic conversion occurs outside the skin predominantly, although both the necessary enzymes, 25-hydroxylase and 1 α-hydroxylase are present in the skin.  Thus the active form of vitamin D,1,25-dihydroxyvitamin D3 may be present in the skin.

While the reaction to form pre-vitamin D3 takes minutes, the reaction converting it to vitamin D3 takes hours to occur and is a rate-limiting step.

The vitamin D3 gets carried to liver, where it gets changes into a more active form; from there, it goes to kidneys, where it becomes even more active.

Some of the vitamin D3 stays in liver and kidneys, where it helps reabsorb calcium from blood.
Synthesis of vitamin D in the skin