8.1 Fat Soluble Vitamins

Question 1

What are the four fat soluble vitamins?

Answer 1

A D E and K

Question 2

How do fat soluble vitamins differ from water soluble vitamins?

Answer 2

• Insoluble in watery GI juices
• Require bile for absorption.
• Many require transport (carrier) proteins
• Absorbed into the lymphatic system
• Stored in cells associated with fat, mainly in the liver and in adipose tissue
• Less readily excreted; do not need to be replenished everyday

Question 3

How do fat soluble vitamins differ from water soluble in absorption into the lumen of the small intestine?

Answer 3

Question 4

What are the two forms of vitamin A?

Answer 4

Question 5

Answer 5

Question 6

How are the different forms of vitamin A interconverted in the body?

Answer 6

• After absorption via the lymph system, vitamin A is stored in the liver
• A special transport protein, retinol-binding protein transports vitamin A in the blood
• The body can convert retinol to other active forms of vitamin A as needed

Question 7

What are the specific functions of each form of vitamin A?

Answer 7

Question 8

What are the two roles of vitamin A (retinal) in the eye?

Answer 8

1. Helps maintain a crystal clear cornea
2. Participates in the conversion of light energy into nerve impulses at the retina.

Question 9

What is the role of rhodopsin in vision?

Answer 9

Rhodopsin, is a pigment molecule within the cells of the retina. Visual activity leads to repeated losses of retinal (as retinoic acid), necessitating constant replenishment from foods or retinol stores

Question 10

Apart from vision what are the three other roles of vitamin A in the body?

Answer 10

• Vitamin A plays a role in cell differentiation and helps the specific functions of:
  
  • Epithelial cells - helps to protect against skin damage from sunlight
  • Goblet cells (glands that secrete mucous) - Vitamin A helps maintain the structural integrity of the mucous membranes (eg. GI tract)
• Vitamin A supports reproduction and growth
  • Supports sperm development in men
  • Supports normal foetal development in women
  • Growth in children (participates in bone remodeling)
• Beta carotene acts as an antioxidant

Question 11

How can vitamin A deficiency give rise to night blindness?

Answer 11

• Night blindness
• First sign of vitamin A deficiency
• Retina does not receive adequate retinal to replace losses (from conversion to retinoic acid)

Question 12

How can vitamin A deficiency lead to complete blindness?

Answer 12

• Blindness (xerophthalmia)
• Is the failure to see at all.
• Caused by lack of vitamin A in the cornea

Question 13

How is vitamin A deficiency associated with infectious disease?

Answer 13

• Vitamin A deficiency is associated with impaired immunity and susceptibility to infectious diseases (eg. Measles)
• Supplementation can help with life-threatening infections (eg. Malaria, HIV)

Question 14

How is vitamin A deficiency associated with keratinasation and mucus secretions?

Answer 14

• In vitamin A deficiency, the epithelial cells secrete keratin (keratinisation) causing rough, lumpy and dry skin.
• Goblet cells also secrete less mucus, which disrupts normal digestion and absorption of nutrients – worsens malnutrition. It also weakens defense mechanisms of the respiratory tract and other tissues.

Question 15

How does vitamin A toxicity occur?

Answer 15

• Toxicity disease is called hypervitaminosis A
• Vitamin A and beta-carotene toxicity can occur with concentrated amounts of the pre-formed vitamin A from animal foods, fortified foods or supplements.

Question 16

What are the side effects of vitamin A toxicity?

Answer 16

• Birth defects
  
  • Excessive vitamin A is teratogenic. High intakes before the 7th week of pregnancy is most damaging.
• Bone defects
  
  • Weakens bones and contributes to fractures and osteoporosis
• Discolouration of skin.
  
  • Overconsumption of beta-carotene from foods may turn skin yellow

Question 17

What are some good food sources of vitamin A?

Answer 17

Question 18

What is vitamin D?

Answer 18

• Vitamin D (calciferol) is a non-essential nutrient that acts like a hormone in the body.
• The skin converts cholesterol to previtamin D3 with help from sunlight.

Question 19

What are the different forms of vitamin D?

Answer 19

• The plant version is called vitamin D2, or ergocalciferol.
• The animal version is called vitamin D3, or cholecalciferol.

Question 20

How is vitamin D activated in the body?

Answer 20

• Once the vitamin enters the body, it must become activated.
• Activation occurs through the action of the liver and the kidneys.
• Calcitriol is the active form of vitamin D.
• A binding protein transports it to target organs (bones, kidneys and intestine).

Question 21

How is vitamin D linked to skin colour?

Answer 21

• Process of natural selection for Africa
• Light skin had less reproductive success
• Sunlight stopped folate being destroyed
• Far north needed light skin to absorb as much sunlight as possible

Question 22

How does vitamin D relate to bone health?

Answer 22

• Vitamin D’s role is to maintain blood concentrations of calcium (Ca) and phosphorus (P). It does this by
  
  • Increasing mineral absorption from the GI tract
  • Mobilisation of calcium and phosphorus from bones into the blood
  • Reabsorption of minerals from the kidneys
• Parathyroid hormone (PTH) and vitamin D work in concert to mobilise Ca from bone and conserve minerals from urine.

Question 23

What are the six factors affecting vitamin D levels?

Answer 23

• Latitude/season/air pollution
• Age
• Skin colour
• Weight
• Diet
• Breastfeeding and certain health conditions

Question 24

How does climate affect vitamin D levels?

Answer 24

• Latitude/season/air pollution
• Vitamin D deficiency is higher during the winter months in some countries due to low sun exposure. Heavy clouds or air pollution block the UV rays needed for vitamin D synthesis

Question 25

How does age affect vitamin D levels?

Answer 25

The ability to produce activated vitamin D drops with age. At age 65, the skin produces only 1⁄4 of that which is produced by someone in their 20s.

Question 26

How does skin colour affect vitamin D levels?

Answer 26

People with darker skin typically have lower levels of vitamin D than lighter-skinned individuals.

Question 27

How does weight affect vitamin D levels?

Answer 27

A BMI above 30 is associated with lower blood levels of vitamin D. Vitamin D is stored in fat, so in people with obesity, less of the vitamin circulates in the blood, where it’s available for use by the body.

Question 28

How does diet affect vitamin D levels?

Answer 28

• Very few foods naturally contain vitamin D. In Australian, vitamin D fortification is mandated for margarines and is voluntary for low-fat milk, powdered milk, yoghurt and soy milk.
• Some cereals and beverages may also be fortified, but this varies by brand. So, the amount of vitamin D you get from food depends on the food you eat and how much milk you drink.

Question 29

How does breastfeeding and certain health conditions affect vitamin D levels?

Answer 29

• People with conditions such as inflammatory bowel disease, liver disease, or cystic fibrosis may have trouble absorbing vitamin D, which can lead to deficiencies.
• Breastfeeding mothers and their infants may become vitamin D deficient.

Question 30

What are the three different deficiencies of vitamin D?

Answer 30

• Rickets (children)
  
  • Condition where bones fail to calcify normally, causing growth retardation and skeletal abnormalities. Bones are weakend and bend giving bowed legs
• Osteomalacia (adults)
  
  • Bones become soft, flexible, brittle and deformed from poor bone mineralisation
• Osteoporosis (adults)
  
  • Develops from poor bone-acquisition during childhood/adolescence and bone loss of late adulthood

Question 31

Where should vitamin D be consumed from?

Answer 31

• Obtained from the sun and from foods:
• Fortified milk, butter and margarine
• Egg yolks and liver
• Fatty fish and their oils
• Vegans likely to require supplements.

Question 32

Why are the elderly more vulnerable to vitamin D deficiencies?

Answer 32

• They lose the capacity to make and activate vitamin D
• They drink little milk
• They spend little time outdoors and when they do they wear protective clothing.
• This can contribute to the bone loss and it’s resulting consequences (fractures).

Question 33

How can vitamin D toxicity arise and its symptoms?

Answer 33

• Vitamin D levels obtained from food and produced by the skin are well within safe limits. However, high- dose supplements may cause toxicity (especially for children)
• Toxicity symptoms:
  
  • Elevated blood calcium concentration (hypercalcaemia)
  • Calcification of soft tissues (blood vessels, kidneys, heart, lungs and tissues around joints). Can cause death if calcification occurs in the major vessels of the heart or lungs.
  • High blood level of calcium can cause frequent urination.

Question 34

What does the vitamin E family consist of?

Answer 34

• Vitamin E family consists of two subgroups: tocopherols and tocotrienols.
• Of all the vitamin E family members, only 􏰃-tocopherol has vitamin E activity.

Question 35

Which of the forms of vitaman E are useful in the body?

Answer 35

• All forms are absorbed in the small intestine, but the liver preferentially selects a-tocopherol with the help of the a-tocopherol transfer protein.
• The others are not converted to a-tocopherol in the body, nor are they recognised by the transport protein
• The liver metabolises and removes the other vitamin E forms.
• Although some work has been done with a-tocopherol, it has been the subject of much less research

Question 36

What are the food sources of vitamin E in the body?

Answer 36

• Polyunsaturated plant oils such as margarine, salad dressings and shortenings
• Green, leafy vegetables
• Wheatgerm
• Wholegrain foods
• Liver and egg yolks
• Nuts and seeds
• As vitamin E is easily destroyed by heat and oxygen, fresh or minimally processed foods are preferred.

Question 37

How does vitamin E function as an antioxidant?

Answer 37

• The main role of vitamin E is to act as an antioxidant, scavenging loose electrons—so-called “free radicals” that can damage cells, particularly the cell membranes (lipid peroxidation).
• The body is exposed to free radicals from the conversion of food to energy, as well as environmental exposures, such as cigarette smoke, air pollution, and ultraviolet radiation from the sun.
• In mopping up free radicals, vitamin E helps to protect the vulnerable components of a cell’s membrane.

Question 38

How can vitamin E be associated with lower atherosclerosis (heart diesease)?

Answer 38

• Vitamin E also protects LDL against oxidation and reduces inflammation – two factors involved in the development of artery clogging atherosclerosis.
• Epidemiological studies show that high intakes of vitamin E are associated with lower rates of death from heart disease.

Question 39

What concerns have been raised about taking antioxidant supplements?

Answer 39

• A few studies have raised the possibility that taking antioxidant supplements, either single agents or combinations, could interfere with health.
• Vitamin E supplements were found to significantly increase the risk of prostate cancer by 17% in healthy men compared with those who took a placebo.
• In the SU.VI.MAX trial, rates of skin cancer were higher in women who were assigned to take vitamin C, vitamin E, beta-carotene, selenium, and zinc.

Question 40

What is the reason why antioxidant supplements did not show health benefits?

Answer 40

• One possible reason why antioxidant supplements do not show health benefits is because antioxidants tend to work best in combination with other nutrients, plant chemicals, and even other antioxidants.
• Differences in the amount and type of antioxidants in foods versus those in supplements might also influence their effects. For example, there are eight chemical forms of vitamin E present in foods. However, vitamin E supplements typically only include one form, a-tocopherol.

Question 41

How can vitamin E deficiency arise?

Answer 41

• Deficiency is rare. Susceptible individuals are those who have digestive disorders or do not absorb fat properly (ie. pancreatitis, cystic fibrosis, celiac disease).

Question 42

What are the signs of vitamin E deficiency?

Answer 42

• Erythrocyte haemolysis (vitamin E treatment corrects haemolytic anemia)
• Retinopathy (damage to the retina of the eyes that can impair vision)
• Neuromuscular dysfunction (loss of control of body movements and speech)

Question 43

How can vitamin E toxicity arise?

Answer 43

• Toxicity is rare; the least toxic of the fat-soluble vitamins
• Upper level for adults: 300 mg/day, which is more than 30 times the recommended level.

Question 44

What are the two forms of vitamin K?

Answer 44

Question 45

What are the roles of vitamin K in the body?

Answer 45

• Vitamin K is required for the synthesis of proteins involved in hemostasis (blood clotting) and bone metabolism, as well as other diverse physiological functions (in the nervous and excretory systems)
• Bone metabolism
  
  • Vitamin K participates in metabolism of bone proteins, most notably osteocalcin. Without vitamin K, osteocalcin cannot bind to minerals to form bonds. Adequate vitamin K helps to improve bone density, decreases bone turnover and protects against fractures.
• Blood-clotting
  
  • Prothrombin (an inactive protein made in the liver) is a vitamin K-dependent protein in plasma that is directly involved in blood clotting. Without vitamin K, a haemorrhagic disease may develop.

Question 46

How can vitamin K deficiency arise?

Answer 46

1. Malabsorption of fat (eg. bile production fails, vitamin K absorption diminishes)
2. Medications interfere with vitamin K synthesis (eg. antibiotics) and action in the body (eg. warfarin and other anticoagulants)
3. Newborns because vitamin K does not cross the placenta and because bacteria in the GI tract take weeks to establish. Newborns are given vitamin K at birth

Question 47

How can vitamin K toxicity arise?

Answer 47

• Toxicity is rare: no known adverse effects of high intakes.
• High intakes can reduce effectiveness of anticoagulant drugs to prevent clotting
• No Upper Level of Intake

Question 48

What are the sources of vitamin K?

Answer 48

• Bacterial synthesis in the digestive tract
• Liver
• Green, leafy vegetables and cabbage-type vegetables.
• People typically get 50% of their vitamin K from bacterial synthesis and 50% from food.
• Because vitamin K is fat-soluble, it is best to eat vitamin K foods with some fat to improve absorption. So, drizzle some olive oil or add diced avocado to your favourite leafy green salad!