Lipid soluble vitamins

Vitamin E

Alpha- tocopherol

Vitamin E function

Antioxidant

Vitamin E RDA

15 Mg/day for adults

Ul for vitamin E

1000 mg/day

Vitamin E absorption

Absorbed with fats

Transport of vitamin E

Incorporated into chylomicrons for circulation, processed in the liver (alpha-tocopherol transfer protein )

Excretion of vitamin E

Excreted via bile and feces , can be excreted via urine but must be processed in the liver

Vitamin E deficiency

Rare, symptoms: erythrocyte hemolysis (red blood cells break due to oxidation of membrane )

Vitamin E food sources

Widely available , especially in vegetable oils ( can be destroyed by heat and oxidation)

Vitamin A

Retinol, retinal,retionoic acid

Vitamin A functions

Light absorbing pigment in the eye ( rhodopsin ),regulation of gene expression

Why is vitamin A required?

Forms rhodopsin in rod cell photoreceptors at the back of the retina

Active form of vitamin A

Retinoic acid

Process of vitamin A in gene expression

Retionic acid → RAR and RXR (receptors) → DNA → Gene expression

Vitamin A RDA?

Men: 900 RAE (retinol activity equivalents)

Women: 700 RAE

Pregnant: 770

Lactating: 1300

Vitamin A UL?

3000 RAE

Vitamin A absorption

Vitamin A as retinal esters is absorbed in small intestines; requires dietaryfat and bile acids(must be esterfied to be absorbed)

Absorption of carotenoids is low

Once absorbed retinol and beta-carotene are metabolized in

Enterocytes before entering blood stream

Vitamin A storage?

Retinyl esters can be stored in hepatic stellate cells

Vitamin A transport?

Retinol binds to retinol binding protein → enables circulation in holo-RBP → delivery mechanism for retinol to other tissues

Vitamin A excretion?

Excreted via bile and feces

Irreversible interconversion

B-carotene → retinal → retinoic acid

Interconversion

Retinyl esters → retinol →retinal → retinoic acid

Vitamin A deficiency?

Night blindness, xerophthalmia, bitot spots

Vitamin A toxicity?

Acute deficiency symptoms: nausea,vomiting,double vision

Chronic deficiency symptoms: birth defects (accutane),anorexia

Vitamin A dietary sources

Animal products, liver, fortified foods

Pro-vitamin A sources?

Carotenoids - plant pigments found in many fruits and veggies

Conversion of pro-vitamins

Conversion of beta-carotene requires enzyme BC01

Vitamin k

Quinone derivative

Vitamin k function

Blood clotting and bone calcification

Gamma carboxylation

Provide the ability for clotting factors like thrombin to bind Ca2+ to be active

Warfarin and vitamin k

Warfarin interferes with recycling of vitamin k→ vitamin k less available → reduction in gamma carboxylation of clotting factors

Vitamin k AI

Men: 120 ug/day

Women: 90 ug/day

Vitamin k ul?

UL is not established

Vitamin k absorption?

Absorbed in small intestines and requires bile, fat, and pancreaticfactors

Vitamin k transportation?

Transported in chylomicrons

Vitamin k storage?

Unlike other fat-soluble vitamins there is limited storage

Vitamin k recycling?

Can use reducing power from NADPH to recycle

Vitamin k deficiency?

Primary deficiency is rare

Secondary deficiency can occur from malabsorption and anticoagulant drugs

Vitamin k food sources?

Leafy greens and gut bacteria

Vitamin D

Cholecalciferol

Vitamin D synthesis?

Synthesis by the skin: produces majority of vitamin D from sun exposure

Vitamin D transport?

Cholecalciferol or vitamin D3 enters bloodstream bound to vitaminD binding protein

Vitamin D activation?

Two step activation: 1) liver: 25 -Ohase 2)kidney: 1 alpha-ohase → final product: 1,25 -

(OH)2 D3 ( calcitriol) = active vitamin D

Regulates its own breakdown, negative feedback

Vitamin D function?

Maintain normal serum calcium and phosphorus levels

Low blood calcium activation/regulation

Parathyroid hormone (PTH) is released from parathyroid gland →PTH activates enzyme that convents inactive vitamin D to active form calcitriol → calcitriol and PTH stimulate production of osteoclasts → calcitrol increases calcium absorption from intestines and reabsorption in kidneys

High blood calcium activation/regulation

Calcitonin: released from thyroid → stimulates addition of calcium and phosphorus to build bone

Calcitriol (active vitamin D)

Facilitates calcium absorption from gut → needed for bone mineralization

Vitamin D mechanisms of action

Vitamin D behaves as a hormone and regulates gene expression by binding vitamin D receptor (VDR)

Vitamin D and immune system

Vitamin D influences immune response and host-defence against pathogens via camp

Vitamin D RDA

600 IU/day

Vitamin D absorption?

Absorption from foods is roughly 50% efficient , occurs in distal ileum of small intestine, requires bile acids and fat

Vitamin D transport/ circulation

Vitamin D is packed into chylomicron for circulation → circulates bound to vitamin D binding protein

Vitamin D deficiencies?

In children: rickets (bowed legs, enlarged head)

In adults: osteomalacia (soft bones)

Vitamin D toxicity?

Toxicity is unlikely from sun exposure and foods and is most likely from excessive supplementation (hypercalcemia,kidney dysfunction)

Vitamin D sources?

Animal foods, the sun, fortified foods

Vitamin D UL?

4000 IU/day

What is true about deficiency symptoms for fat-soluble vitamins?

Deficiency symptoms sometimes take a long period of time to develop after insufficient intake