Chapter 11 fat soluble vitamins

Fat Soluble Vitamins


Fat Soluble Vitamins
• Vitamin A
• Vitamin D
• Vitamin E
• Vitamin K


General Properties
• Soluble in...?
• Excess is stored in the body
• Stored in fatty tissues and in the liver
• Can be toxic


General Properties
• Not excreted in urine
• Deficiencies develop slowly
• More stable to heat and cooking
• Contain C, H, O


General Properties
• Absorption
– Small Intestine
– Lymph system
• Transport
– Many require Proteins as carriers

General Properties
• Storage
– Cells associated with fat
• Excretion
– Tends to remain in storage site


General Properties
• Toxicity
– Likely to reach to levels when
consumed from supplements
• Requirements
– Needed in periodic doses
– weeks to months


RDA Terminology
• Vit A: mcg - retinol equivalents (RE)
• Vit D: mcg - Cholecalciferol
• Vit E: mg - alpha () Tocopherol
• Vit K: mcg


Vitamin A
• First fat soluble vitamin
• Beta-carotene is its PRECURSOR


Vitamin A

• Active forms in the body:
– Retinol
– Retinal
– Retinoic Acid
– All are called RETINOIDS


Forms of Vitamin A


Vitamin A
• Animal sources contain retinoids
– Retinyl esters (preformed vit A)
• Plant foods
– Carotenoids: Beta-carotene
(provitamin A)
– Can be converted to retinol
• intestine and liver


Retinoids


Vitamin A
• Each form has specific function
• 90% storage in the liver


Vitamin A
• Cells can convert retinol and retinal

to other active forms
• Retinol

Reversible

• Retinal

Retinal
Retinoic Acid

Irreversible


Vitamin A
• Absorption
– micelles...
• How do we transport fat???


Roles of Vitamin A
• Promotes vision
– Retinal
– Also intermediate between retinol
and retinoic acid


Vitamin A and Vision


Roles of Vitamin A

• In DIM LIGHT:
– vitamin A + opsin --------> rhodopsin
(visual purple)
• In BRIGHT LIGHT the reverse occurs:
– rhodopsin ---------> vitamin A + opsin


Roles of Vitamin A
• Protein Synthesis and cell
differentiation
– Retinoic acid
– Acts like a hormone
– Regulates differentiation, growth
and development


Roles of Vitamin A
• Cell differentiation


Roles of Vitamin A
• Reproduction and growth
– Retinol
– Retinol is the major transport and
storage form
– Men
sperm
– Fetal development
– Bone remodeling

Beta-carotene
• Orange pigment of foods
• Vitamin A precursor
• Antioxidant


Vitamin A Deficiency
• Deficiency appear after 1-2 years
(adults)
• Developing world nutrition problem
• Susceptible to infectious disease
and blindness


Vitamin A Deficiency
• Night Blindness
– one of the first signs of vit A
deficiency
– lack of retinal
– people cannot see in the dark