TOPIC 26; Fat-soluble vitamins

What are the fat-soluble vitamins?

ADEK

Vitamin A?

Retinol

What is the function of Vit A?

Essential cofactor for the normal function of rhodopsin in the rods

- which is what senses light in the retina

Also important for embryonic development and normal function of the epithelium

Where is Vit A stored?

In hepatic stellate (Ito) cells

= liver

Typical sources of Vit A?

- Orange vegetables, like pumpkin, tomato and carrots

- Liver

RDA of Vit A?

900 microgram

What are the typical causes for Vit A deficiency?

- Regions where rice is main source of calories

- Chronic diarrhoea

- Liver cirrhosis

- Lack of bile (which is necessary for absorption)

Hypovitaminosis of Vit A?

- Xerophthalmia

- Nyctalopia (night blindness)

- Dry and hyperkeratotic skin

- Squamous metaplasia in the upper respiratory tract

- Abnormal embryonic development

What is xeropthalmia?

Dry eyes

- increased susceptibility for infections in the eyes, which may cause blidness

Hypervitaminosis of Vit A?

- Acute intoxication; increased intracranial pressure

- Chronic intoxication; mildly increased ICP, liver damage, joint pain and hair loss

- Highly teratogenic

Pharmaceutical use of vit A?

Treatment of acne

Vitamin D?

Calcitriol

What is the function of Vit D?

- Increase Ca2+ and Po4-3 absorption from the GI-tract

- Enhance Ca2+ resorption from bone

- Enhance Ca2+ reabsorption in the kidney

= Increase serum calcium levels

Where is Vit D stored?

Liver and adipose tissue

Typical sources of vit D?

- Can be synthesized in the body

- Fish, meat and milk

How is Vit D synthesized?

- Cholesterol is converted into cholecalciferol in skin exposed to UV radiation

- Cholecalciferol is converted into 25-hydroxycholecalciferol in the liver

- 25-hydroxycholcalciferol is converted into 1,25- dihydroxycholecalciferol in the kidney

The last step requires PTH

RDA of Vit D?

10 microgram

What are the typical causes of Vit D deficiency?

- Lack of skin exposure to sunlight

- Chronic diarrhoea

- Lack of bile

- Liver or renal failure

- Lack of PTH

- Rapid growth, pregnancy, lactation

Hypovitaminosis of Vit D?

- Hypocalcaemia

- Caries

- Bone pain

- Stunted growth and bone deformities, called rickets in children and osteomalacia in adults

Hypervitaminosis of Vit D?

Hypercalcaemia

-> metastatic calcification

Vitamin E?

Tocopherol

What is the function of Vit E?

- Vit E is an antioxidant

- Stabilizes membranes of erythrocytes, the nervous system and of muscles

Where is Vit E stored?

Adipose tissue

Typical sources of Vit E?

Nuts and seeds

RDA of Vit E?

10-30mg

What are the typical causes of Vit E deficiency?

- Lack of bile

- Chronic fasting

- Increased requirement in rapid growth and preterm infants with IRDS

- Deficient when there is deficiency of betalipoproteins, which carries it in the plasma

Hypovitaminosis of Vit E?

- Haemolytic anaemia

- Increased risk for infections

- Muscle weakness

Hypervitaminosis of Vit E?

- Hepatosplenomegaly

- Jaundice

- Ascites

- Completes for Vit K absorption, and therefor causes Vit K hypovitaminosis if overdosed

Vitamin K?

Phylloquinone

What is the function of Vit K?

Essential for the synthesis of;

- clotting factors II, VII, IX, X

- anticoagulant factors protein C and S

Where is Vit K stored in the body?

Not significant

- only stored for a week

Typical sources of Vit K?

Produced by enteric bacteria

RDA of Vit K?

120 microgram

Typical causes of Vit K deficiency?

- Chronic diarrhea

- Lack of bile

- Coumarins

- Infants are often deficient, as they have ha no time to build up their stores and the breast milk doesnt contain Vit K

What do we do about the low concentration of vit K in infants?

Infants receive 0.5-1mg vitamin K intramuscularly

- to prevent vit K deficiency bleeding

Hypovitaminosis of Vit K?

Coagulopathy

- prolonged prothrombin time

Hypervitaminosis of Vit K?

- Increased risk of thrombosis

- Kernicterus

Why does increased Vit K levels cause kernicterus?

Because Vit K competes with bilirubin for albumin-binding

- increased Vit K = increased levels of free, unconjugated bilirubin in the serum