CHEM215 Lecture Notes - Lecture 23: Chronic Toxicity, Nyctalopia, Xerophthalmia
Lecture 23 – Vitamins 2
Fat-soluble vitamins:
• have non-polar structures and can therefore accumulate in fatty body tissues.
• Diet deficiencies do not manifest themselves immediately (as opposed to water
soluble vitamins in which deficiencies occur quickly).
• Hypervitaminosis can occur —> much easier get too much of fat-soluble vitamins.
• In general, fat-soluble vitamins are more soluble and not as heat sensitive
Vitamin A:
• Several forms of vitamin A called retinoids.
• Sources —> liver, butter, cheese, fish oils, eggs. Also made from dietary
carotenoids (found in spinach, dark leafy greens, broccoli, deep orange furies and
vegetables). These contribute to half of vitamin A intake.
• Stability —> retinol is stable to processing/cooing by carotenoids are less so.
• Requirements —> intakes are generally expressed in terms of retinol equivalents
(RE). 1 RE is defined as the biological activity associate with 1 ug of all-trans
retinol.
• Biochemical roles —> a form of vitamin A, retinal, combines with the receptor
protein, opsin, to give rhodopsin. Night blindness can occur in people
with deficiency in Vitamin A, due to lack of production of rhodopsin which is
used for black and white vision.
• Vitamin A is also an antioxidant —> absorbs radicals, so protects against oxidative
damage - damage caused by reactive radicals.
• Deficiencies —> symptoms of deficiencies include night blindness, xerophthalmia
(drying and degeneration of cornea of eye), and abnormal bone development.
• Toxicity —> can be stored in body so toxic effects are not uncommon either due
to auto toxicity (single high dose) or long term over consumption (chronic
toxicity).
Acute toxicity can result in coma and death.
Chronic toxicity can cause weight loss, muscle and joint pain, liver damage, bone
abnormalities and visual defects.
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Lecture 23 – Vitamins 2
• The vitamin A content of mamallain livers varies widely —> polar bear livers are
poisonous to humans due to their extremely high Vitamin A content. Vitamin A
toxicity occurredin the Australian Antarctic Expedition, as they were forced to eat
their dogs livers which contain a lot of vitamin A.
• Deficiency can occur in:
-breast-fed infants
-preschoolers with poor vegetable intake
-urban poor
-elderly
-alcoholics and people with liver disease
-HIV/AIDS sufferers.
Vitamin D:
• Two forms:
-Vitamin D3 —> cholecalciferol form in skin from UV light. UV light acts on a
cholesterol molecule to form this D3.
-Vitamin D2 —> readily synthesised from ergocalciferol. This is used in
pharmaceutical
applications.
• Synthesis —> epidermal cells of skin contain 7-dehydrocholesterol which
is converted into cholecalciferol by the action of UV components of
sunlight.
• Sources —> found in liver oils of fish.
• Biochemical role—> required for appropriate regulation of calcium in body.
Calcifetriol, calcitonin and parathyroid hormone, produced by the hydroxylation
of vitamin D, are hormones that regulate Ca2+ metabolism in the body. Lack
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