2. Definitions

#### 2.1 Vitamins

Vitamins are organic compounds essential in small quantities for normal physiologic and metabolic functioning of the body [1]. Vitamins are a large family usually grouped as micronutrients; they are mostly derived from diets with few exceptions and unlike other food substances, this family of micronutrients usually exist in complexes with one another and thus cannot be obtained from a single dietary source.

Functionally, vitamins are involved in various metabolic processes where they serve usually as coenzymes in various biochemical reactions associated with proper functioning of the whole organism [2]. They thus catalyze organic reactions by participating in the formation of hormones, cells, chemical structures of the nervous system, composition of genetic material and a host of other biological processes. They also combine with proteins to form enzymes which participate in various body reactions including in the development of body's immune system.

processes. The focus of this chapter is however on vitamin D with particular emphasis on its plant sources and medicinal applications in sub-Sahara Africa.

Plant Sources of Vitamin D and Its Medicinal Application in Sub-Sahara Africa

tions in human metabolism. It exists in five active forms

ii. 24,25-dihydroxyvitamin D3(24R,25-(OH)2D3

i. 1,25-dihydroxyvitamin D3(1,25-(OH)2D3,

iii. 1,25-dihydroxyvitamin D2(1,25-(OH2)D)

process. Sea fatty fish essentially contain vitamin D2.

3.2 Plant sources of vitamin D

iv. 25-hydroxyvitamin D3(25-OH-D3)

DOI: http://dx.doi.org/10.5772/intechopen.81851

v. 25-hydroxyvitamin D2(25-OH-D2)

3.1 Sources and production of vitamin D

Vitamin D is one of the fat-soluble vitamins that has distinct biochemical func-

The general conception is that vitamin D is synthesized only in the body, however, evidences abound that vitamin D is available in different forms in some plants and fruits in sub-Sahara Africa. There are also reports on application of these plant sources in the treatment of some vitamin D related diseases. Vitamin D2 (ergosterol) has been identified in some plants and fungi. Vitamin D2 differs from D3 in having a double bond between C22 and C23 and a methyl group at C24 in the side chain. D2 can be considered the first vitamin D analog which is converted to D3 by ultraviolet radiation. As earlier stated, plants like perennial ryegrass contain some amounts of ergosterol which when ingested can also be readily converted to D3 in

Vitamin D3 has many dietary sources. The parent compound (D2) is derived essentially from dietary sources like egg yolk, sea fatty fish, liver, and mushroom among others. The production of vitamin D3 (D3) in the skin is not an enzymatic

Accidental discovery of activation of some vegetables and crops by exposure to

mercury lamp led to the identification of vitamin D2 in some inert foods like cottonseed, wheat and lettuce [4]. Later, vitamin D2 was identified from solutions of ergosterol irradiated with UV light in-vitro [5]. Hence, contamination of plants with fungi which has a high concentration of ergosterol led to the discovery of "plants contaminated with fungi" as veritable source of vitamin D2. This initial concept on the presence of vitamin D in plants however changed with the discovery of a type of calcium intoxication in grazing animals similar to that caused by vitamin D toxicity that consumed certain plants [6]. This was believed to be due to vitamin D3 or a metabolite of vitamin D3 present in the plants that stimulate calcium absorption producing hypercalcemia and deposition of calcium in soft

Hence, while plants like Solanum glaucophyllum Desf. (S. glaucophyllum), Cestrum diurnum L. (C. diurnum) and Trisetum flavescens Beauv. (T. flavescens) were found to cause calcium intoxication similar to that caused by vitamin D toxicity in

tissue including aorta, heart, kidneys, intestines, and uterus [6].

3. Vitamin D

the body [3].

9

Probably because vitamins are present in small quantities, in the past, diseases of vitamin deficiencies were treated using various vitamins supplementarily in their management; however, advancement in science has led to many biochemical and biological methods that are appropriately used in the identification, measurement and diagnosis of diseases associated with many of the known vitamins.

Due to the involvement of these vitamins in several metabolic processes in spite of their small quantities, their deficiencies usually manifest clinically in various forms; for example, pellagra and beriberi are clinical conditions associated with the deficiency of niacin and thiamine respectively, (sub-groups of vitamin B), scurvy is a clinical condition associated with vitamin C deficiency, while osteomalacia (in adults) and rickets (in growing children) are associated with vitamin D deficiencies. Night blindness is associated with vitamin A deficiency, deficiency of vitamin B12 or that of folic acid is associated with megaloblastic anemia while spinal bifida has been associated with the deficiency of folic acid in the mother while the baby was in-utero [2]. Because vitamins as essential nutrients are mostly derived from diets, etiology of hypovitaminosis has always been associated with either in-adequate intake from diet or abnormality of absorption whereby a large quantity of these essential nutrients remains unabsorbed even when present abundantly in diet. Generally, vitamin toxicity is associated with the fat-soluble series because of their insolubility in the aqueous medium which largely constitutes the human system; however, excessive ingestion of vitamin A has been known to result in toxic manifestations which may ultimately result in liver damage [2].

#### 2.2 Classification of vitamins

Vitamins are generally classified based on their solubility in aqueous or lipid medium. Thus, there are the fat-soluble vitamins (A, D, E and K) and the watersoluble ones (vitamins B complex and C). Although they are usually classified into these two broad groups, the classification is for convenience based on the chemical structure of vitamins; most of the vitamins have sub-groups that are no less prominent in name as the known main group. For example, while vitamin A is available either as the plant (carotenoid) or animal (retinol) types, vitamin B has several sub groups which have been distinctly classified based on structure and function. On the other hand, the name vitamin E, which is a known fat-soluble vitamin, refers to a family of eight naturally occurring homologs that are synthesized by plants from homogentisic acid. They are all derivatives of 6-chromanol and differ in the number and position of methyl groups on the ring structure. Also, vitamin D is another classical example of a lipid-soluble vitamin. The name, vitamin D, refers to about 5 different compounds generally classified as such, these are: 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3, 24,25-dihydroxyvitamin D3 (24R,25-(OH)2D3, 1,25 dihydroxyvitamin D2 (1,25-(OH2)D), 25-hydroxyvitamin D3 (25-OH-D3), 25 hydroxyvitamin D2 (25-OH-D2). Hence, the general classification of vitamins notwithstanding, several sub-groups of vitamins exist which when considered based on structure, function and activity will make the conventional broad classification of vitamins too simplistic in terms of their overall relevance in human metabolic

processes. The focus of this chapter is however on vitamin D with particular emphasis on its plant sources and medicinal applications in sub-Sahara Africa.
