W31 Nutrition- Micronutrients (Vitamins)

Question 1

What type of nutrient is water?
What are its roles? (5)

Answer 1

MACRO-Nutrient (principle component of body)
IT does not provide energy

• Needed for nearly all the cellular reactions
• SOLVENT -It moves nutrients and waste within/between cells/tissues/organs
• Maintain the body temperature- Thermoregulation
• Moisten tissues (in the eyes, nose and mouth) and lubricate joints
• Protect your spinal cord and other sensitive tissues
• Dispose of through urination, perspiration, and bowel movements

Question 2

What is water balance?
What contributes the body’s water intake? (3)

Answer 2

The balance between water intake and output (loss)
Based on drinks, food and cellular metabolism

Question 3

What is the minimum obligatory water excretion?
How can fluid be lost through illness?

Answer 3

500mL
Vomiting, diarrhoea, haemorrhage

Question 4

What is dehydration?
What are the symptoms of mild/severe dehydration?

Answer 4

Hypohydration
Reduced water intake causes a thirst sensation (promoted by the hypothalamus) to stimulate the water intake and restore the water balance

Mild (< 5% body weight) - dry skin and mouth, tiredness, lack of concentration
Moderate (5-10%)
Severe (>10%) - seizures, kidney failure and even death

Question 5

What is Overhydration?
What is Water intoxication?

Answer 5

Excessive water intake that affects the electrolyte concentrations and could result in electrolyte imbalance. Urine production is significantly increased

In rare cases, usually kidney disorders, drinking excessive amounts of water can lead to intoxication - hyponatraemia (due to low levels of sodium in the blood).

Question 5

Minerals:
Do they provide energy
What are their roles?

Answer 5

Essential micronutrients- Do not provide energy

Roles-
-Many serve as electrolytes
-Regulate fluid balance, blood pH and are critical for nerve and muscle function (action potential, neuromuscular junction, cell signalling

Question 6

Minerals
What are major and trace minerals?

Answer 6

MAJOR minerals
* >100mg required per day
* Sodium, Potassium, Chloride, Calcium, etc

TRACE minerals
* <100mg required per day
* Iron, Copper, Zinc, Selenium, Fluoride, etc

Question 7

What are enzymes?
What are required to activate enzymes?

Answer 7

Enzymes are proteins (except ribozymes) that act as biological catalysts that speed up specific enzymatic reactions by reducing the activation energy.

Cofactors
e.g.
1. Essential ions
- Activator ions (loosely bound)
- Metal ions for metalloenzymes (tightly bound) (tightly bound)
2. Coenzymes
- Cosubstrates (loosely bound)
- Prosthetic groups (tightly bound)

Question 8

What is a holoenzyme?
What is an apoenzyme?

Answer 8

A complete catalytically-active enzyme together with its cofactor is called a
HOLOENZYME

The protein part of the enzyme on its own without its cofactor is called an apoenzyme (not active).

Question 9

Do vitamins provide energy?
What are their roles? (3)

Answer 9

No
1. Essential for metabolic processes
2. Assist enzymes as coenzymes
3. Act as individual units

Question 10

What are the 2 classes of vitamins?

Answer 10

WATER SOLUBLE
LIPID SOLUBLE

Question 11

What are water-soluble vitamins?
What vitamins are water-soluble?

Answer 11

*Excess excreted via kidney by urine
* Increased risk of deficiency
* Decreased risk of toxicity (excessive intake)
➢ Vitamins B and vitamin C

Question 12

What are lipid-soluble vitamins?
What vitamins are lipid-soluble?

Answer 12

• Excess stored in the body (usually in
  liver)
• Decreased risk of deficiency
• Increased risk of toxicity
  ➢ Vitamins A, D, E & K

Question 13

Water soluble Vitamins – B group vitamins (for info)

Answer 13

B group vitamins (B1, B2, B3, B5, B6, B7, B9, B12)
▪ Serve as coenzymes to Assist enzymes (to release energy)
▪ But they do not directly provide the body with fuel
▪ May have overlapping functions
▪ Named in order of discovery, B4, B8, B10, B11 no longer classified as vitamins
as it was found that they are produced by the body
▪ Some can be synthesised by bacteria of the intestinal flora (Mutualism)

Question 14

What are the roles of Vitamin B1 - Thiamine?
Where are they sourced from?

Answer 14

• Part of the coenzyme TPP (thiamin pyrophosphate)
• To activate many enzymes (holoenzymes) involved in:
  ▪ Carbohydrates catabolism (e.g. pyruvate oxidation into acetyl-CoA – lecture 6)
  ▪ Neuronal action potential conduction & neuro-muscular transmission
• (Whole grains, legumes, pork as the richest source, fruits, and yeast)

Question 15

Thiamine deficiency:

Answer 15

• Thiamine Deficiency
  ▪ Malnourished – inadequate intake
  o Prevalent in diets largely based on white rice (low content of B1)
  ▪ Alcohol impairs thiamine absorption
  ▪ Athletes and pregnant women with high carbohydrate catabolism
• No risk of toxicity

Beriberi - Prolonged thiamine deficiency, affecting different organ systems
➢ Dry beriberi – affects nervous system (paralysis, peripheral neuritis)
➢ Wet beriberi – affect cardiovascular system (cardiac failure characteristic oedema)
➢ Wernicke–Korsakoff syndrome - severe form of dry beriberi (mental
confusion, jerky eye movements, memory loss)

Question 16

Vitamin B2 - Riboflavin
What are its roles?
Where is it sourced from?

Answer 16

Part of the coenzymes FMN (flavin mononucleotide) and FAD (Flavin
adenine dinucleotide)
▪ FAD assists enzymes involved in energy metabolism
▪ FAD is an electron carrier/acceptor during the citric acid cycle (lecture 6)

Sources - Dairy products, eggs, green vegetables and almonds

Vitamin B2 Deficiency
▪ Only common in developing countries
▪ Symptoms - inflammation of the mouth, lips, and GI tract (stomatitis)
* No risk of toxicity

Question 17

Vitamin B3 – Niacin
What are its roles?
Where is it sourced from?

Answer 17

• Part of the coenzyme NAD (Nicotinamide adenine dinucleotide) and NADP
  (Nicotinamide adenine dinucleotide phosphate)
  ▪ Both act as coenzymes of enzymes involved in oxidorectuctase metabolic reactions (NAD - catabolic and NADP - anabolic)
  ▪ NAD is an electron carrier during glycolysis and citric acid cycle
  NAD++ H+ + 2e- ⇄ NADH

Sources - Meat, poultry, fish, and nuts

Question 18

Vitamin B3- Niacin
Deficiency
Toxicity

Answer 18

• Body can make vitamin B3 from the tryptophan (essential amino acid)
  -Only after protein synthesis needs are met (using tryptophan excess)
• Vitamin B3 Deficiency
  o In diets based on maize (low content of niacin and tryptophan)
  o Chronic alcoholics also at risk

 Pellagra - characterised by the 3D’s
 Dermatitis (skin inflammation), Diarrhoea and Dementia

Vitamin B3 toxicity – large dose of nicotinic acid (supplements / food)
* Skin flushes, liver damage

Question 19

Vitamin B5 – Pantothenic acid
What are its roles?
Where is it sourced from?

Answer 19

• part of the coenzyme A, which acts as a coenzyme ofenzymes crucial to many metabolic pathway, such as:
   Enzyme converting pyruvate into acetyl-CoA
   Fatty acids activation (in fatty acyl CoA) to enter the β-oxidation cycle

Sources
* Widespread in foods
* Very rare case of vitamin B5 deficiency

Question 20

Vitamin B6
What are its roles?
Where is it sourced from?

Answer 20

Three forms of vitamin B6 - Roles
* converted to the coenzyme PLP (pyridoxal phosphate), of many enzymes of numerous reactions (>100), e.g.:
 In tryptophan metabolism (link to vitamin B3 synthesis)
 Synthesis of neurotransmitters, haem, nucleic acids
 Urea metabolism

Sources - Meats, fish, poultry, potatoes and other starchy vegetables and intestinal normal flora release vitamin B6

Rare deficiencies – usually in alcoholics
* Alcohol contributes to the destruction of vitamin B6
* Neurological, anaemia, inflammation

• Toxicity can cause nerve degeneration

Question 21

Vitamin B7 - Biotin
What are its roles?
Where is it sourced from?

Answer 21

Roles
* It is a coenzyme itself
* Critical to assist enzymes of the citric acid cycle and other

Sources
 Widespread in natural foods
 Also, vitamin B7 id produced by bacteria in the GI

Deficiencies rarely occur
* Risk for people who eat large amounts of raw eggs, as a protein in egg white seizes biotin and reduces its absorption
* Symptoms include skin rash, hair loss, and neurological impairment

Question 22

Vitamin B9 – Folic acid / folate
What are its roles?
Where is it sourced from?

Answer 22

Roles
* Converted to coenzyme THF (tetrahydrofolate) of enzymes:
involved in the biosynthesis of nitrogenous bases (DNA/RNA),amino acids and the embryonic development of the spinal cord

Sources - Dark green and leafy vegetables, legumes, fruits, nuts

Deficiency - pregnant women and people with cancer are at risk
* Some anti-cancer drugs (e.g. methotrexate) interfere with folic acid synthesis
* To support baby’s development, folic acid supplement in pregnancy (first 12 w)

Effects
* In pregnancy - low birth weight, premature birth and neural tube defects (spina bifida)
* Also, megaloblastic anaemia (larger RBCs) due to faulty erythrocyte multiplication and maturation

Question 23

Vitamin B12 – cobalamin
What are its roles?
Where is it sourced from?

Answer 23

Roles
* Converted to 2 active forms -coenzymes of enzymes involved:
 Production of THF coenzyme from folic acid (vitamin B9)
 Regulation of cell replication and nerve activity

Sources - Foods of animal origin (meat, fish, poultry, shellfish)

Deficiency (some are consequences of reduced Vitamin B9)
* Megaloblastic anaemia,
* gastrointestinal (diarrhoea, loss of bladder control)
* neurological symptoms (seizures, degeneration of spinal cord)

Question 24

Vitamin C – ascorbic acid
What are its roles?
Where is it sourced from?

Answer 24

Roles
* coenzyme of enzymes involved in: the synthesis of collagen
(connective tissue of bones, teeth, tendons), carnitine (fatty acids transporter), steroids, etc
* Potent antioxidant to neutralise free radicals

Sources - Citrus fruits/juices, tomatoes, potatoes, other vegetables

Deficiency (rare in developed countries)
Scurvy - swollen gums, bruising, haemorrhage, bone fracture, loose teeth, poor wound healing and anaemia

Toxicity – GI distress after very large dose

Question 25

Which vitamins are lipid-soluble? (4)

Answer 25

Vitamins A, D, E, K

Question 26

Vitamin A – Retinol / retinal / retinoic acid
What are its roles?
Where is it sourced from?

Answer 26

Roles – it does NOT form a coenzyme
* Three forms (retinol, retinal, retinoic acid). Stored in the liver
* Promoting vision (major role in eyesight)
* Participating in protein synthesis and cell differentiation,
* Supporting reproduction and regulating growth

Sources
* (Retinol): fortified milk, fish, liver
* (carotenoids): broccoli, spinach, orange fruits, carrots

Question 27

Vitamin A deficiencies

Answer 27

Deficiency:
* Night blindness - Blindness after the sun goes down due to corneal damage
-Failure to adapt vision after changes of lights (flash of bright light at night or after dark)
* Keratinisation - dry/ hyperkeratotic skin, skin infection
* Xerophthalmia - Corneal damage. Total blindness

Toxicity – large dose of supplements
* Skin rush, hair loss, liver and bone abnormalities
* Toxicity in pregnancy can lead to birth defects

Question 28

Vitamin D – calciferol
What are its roles?
Where is it sourced from?
Deficiency leads to…
Toxicity..

Answer 28

It comes in two major forms. Vitamin D2 and D3
* Sunlight UVB induces the synthesis of pre-vitamin D3

Roles
* Regulate calcium in the blood (mineralization of bones)
* Regulates the keratinocyte turnover in the skin

Sources
* Synthesized in the uncovered skin with the help of sunlight (UVB)
* Diet: fortified milk, liver, fatty fish (salmon, sardines)

Deficiency
* rickets (children)- distortion of the long bones of the legs, pelvis, spine
* osteomalacia (adults) - leading to bone softening and osteoporosis

Toxicity
* Hypercalcaemia - calcium deposits in organs (e.g. kidneys, liver, heart),
anorexia, insomnia, abnormal bone formation

Question 29

Vitamin E – calciferol
What are its roles?
Where is it sourced from?
Deficiency leads to…

Answer 29

Group of compounds called tocopherols

Roles
* Act as an antioxidant against free radical species
-Involved in smooth muscle growth and the maintenance of nerves

Sources (degraded by heat) - Vegetable oils, nuts, seeds, whole grains
* Usually due to malabsorption of fat rather than lack of dietary intake
* Symptoms include nerve damage and anaemia

Deficiency (extremely rare)
* Augments the effects of anticlotting drugs

Question 30

Vitamin K – calciferol

Answer 30

There are three forms of Vitamin K (K1, K2, K3) -

Roles
* Acts as a coenzyme to assist the formation of coagulation factors
* participates in the metabolism of bone proteins, osteocalcin

Sources
* Green leafy vegetables, broccoli, brussels sprouts, and cabbage
* Vit. K2 - Produced by bacteria of the gut flora

Deficiency - rare
* Liver damage (e.g. alcoholics) or newborns with sterile intestines (no gut flora)
* anaemia, bruising and bleeding at the mucosal membranes (e.g. gums, nose)

No toxicity known. Not stored in great quantities in the liver