Vitamins are organic compounds occuring in natural food either as such or as utilizable Precursors which are required by the body in trace ammounts to perform specific cellular functions like growth and reproduction.

Vitamins are different from other food stuffs,

Donot enter into tissue structure like proteins.

Donot undergo degradation to provide energy like carbohydrates and lipids.

Vitamins are categorized based on their solubility:

1. Water soluble vitamins

2. Lipid (Fat) soluble vitamins

Water soluble •Polar and hydrophilic

•Hetrogenous

•Water soluble, absorbed along with water.•Donot require specific binding proteins for transport.

Fat soluble vitamins•Apolar and hydrophobic•Isoprene derivatives except vit.D which is sterol derivative.•Fat soluble,absorbed along with fats.

•TPT along with lipoproteins or specific binding proteins.

•Excreted in the urine.

•Not stored in the body therefore required daily.•Non toxic•Act as coenzymes

•Not readily excreted in the urine but via bile.•Stored in liver and adipose tissue.

•Excess can be toxic•Vit.K act as coenzyme,D and A are more like a hormone in function.E is antioxidant.

Vitamin A (retinoids) is essential for growth, reproduction,vision and maintenance of epithelial tissues.

Preformed vitamin ARetinoids (retinal, retinol, retinoic acid)

Found in animal products Provitamin A

Carotenoids Must be converted to retinoid formIntestinal cells can split carotene in two (molecules of retinoids)

Found in plant products

Vitamin A in FoodsPreformed(Retinoids)

Liver, fish oils, fortified milk, eggs, other fortified foods

Provitamin A (carotenoids)Dark leafy green, yellow-orange vegetables/fruits

RECOMMENDED DIETARY ALLOWANCE (RDA)1000 Retinol equavelents for males and 800

RE for females.

1 Retinol equavalent = I μg of retinol,6 μ g of ß carotene or 12 μ g of other carotenoids.

Absorption of vitamin A

FUNCTIONS OF Vit.AVISUAL CYCLERhodopsin,the visual pigment of the

rod cells in the retina,consists of 11-Cis retinal specifically bound to protein opsin.

Growth and Differentiation of Cells • Retinoic acid is necessary for cellular

differentiation• Important for embryo development, gene

expression

• Retinoic acid influences production, structure, and function of epithelial cells that line the outside (skin) and external passages (mucus forming cells) within the body.

GROWTH AND REPRODUCTIONRetinol and Retinal are essential

for normal reproduction,supporting spermatogenesis in male and preventing fetal resorption in females.

ACNE AND PSORIASISRetinoic acid and its derivatives

are used to treat acne.Mild acne is topically treated with Tretinoin.

Severe acne is treated with Isotretinoin ,administered orally.

Prevention of chronic diseasesβ Carotene decreases the incidence

of lung and skin cancer.β Carotene functions as an

antioxidant.

Deficiency of Vitamin AMost susceptible populations:

Urban poorAlcoholismLiver disease (limits storage)Fat malabsorption

Consequences:Night blindnessDecreased mucus productionDecreased immunityBacterial invasion of the eyeConjunctival xerosisBitot’s spotsXerophthalmiaIrreversible blindnessFollicular hyperkeratosisPoor growth

Toxicity of Vitamin AAcute – short-term megadose (amounts exceeding 7.5mg/day); symptoms disappear when intake stops GI effectsHeadachesBlurred vision

Teratogenic (may occur with as little as 3 x RDA of preformed vitamin A)Tends to produce physical defect on developing fetus as a result of excess vitamin A intake

Spontaneous abortionBirth defects