Vitamin and Trace Elements

Question 1

What are vitamins?

Answer 1

• Vitamin is general term for a number of unrelated organic substances that occur in food and are required in trace amounts (μg to mg quantities per day)
• Essential micronutrients with diverse biochemical functions which cannot be synthesised in the organism, or are not made in sufficient quantity
• Humans require 13 vitamins: 4 fat soluble (A, D, E, K) and 9 water soluble (C and 8 B vitamins)

Question 2

What are examples of Nutritional Deficiency?

Answer 2

• Deficiency of vitamins and trace elements relatively uncommon in developed world
• Worldwide vitamin A, iodine and iron deficiencies are a major health problem
• Deficiency may be due to poor diet e.g. alcoholism, malabsorption, Inborn error of metabolism, food fads
• When deficient or inadequately absorbed, characteristic clinical disorders arise
• For most micronutrients, a recommended dietary allowance (RDA) has been agreed
• Where evidence is lacking, an adequate intake (AI), based on observation, is use
• Micronutrients generally function as gene activators, free-radical scavengers, or coenzymes or cofactors in metabolic reactions
• Excessive intakes of micronutrients can result in toxicity

Question 3

How are Vitamin Absorbed?

Answer 3

Water-Soluble Vitamins (Vitamin B and C)

• Enter the villi from lumen of intestine via simple diffusion
• Travel through the body via blood vessels

Fat-Soluble Vitamins (Vitamins A, D, E, K)

• Solubilised by Micelles. Move from lumen to intestine through epithelial cells together with long fatty acids and monoglycerides via simple diffusion
• Store in body for long period of times which known as lipocytes

Question 4

What are forms of Vitamin A?

Answer 4

• Alcohols (retinols)
• Aldehydes (retinals)
• Retinoic acid

Question 5

How do Retinols get formed and how is it used?

Answer 5

• The body can convert β-carotene and other carotenoids to retinol
• Retinol is the principal circulating form
• Retinoic acid binds to retinoic acid receptors (RAR) and to retinoid X receptors (RXR)
• RAR/RXR heterodimers function as ligand-dependent transcription factors and account for many of the pleiotrophic effects of retinoids

Question 6

How is Vitamin A stored?

Answer 6

• Stored in liver, requires transport proteins to be mobilised. Plasma vitamin A does not fall until hepatic stores are severely depleted
• Adequate vitamin A does not necessarily reflect adequate liver stores

Question 7

How is Vitamin A transported in the body?

Answer 7

• Bound to retinol binding protein (RBP) and pre-albumin. RBP is a negative acute phase reactant so may result in apparent low vitamin A
• Evidence vitamin A can decrease by as much as 50%
• Renal failure may increase RBP and therefore vitamin A
• Zinc is required for RBP synthesis

Question 8

What are sources of Vitamin A?

Answer 8

• Spinach
• Tomato
• Potation
• Carrots
• Eggs
• Dairy

Question 9

What are functions of Vitamin A?

Answer 9

• Vision: 11-cis-retinal binds to opsin to form rhodopsin, the visual pigment in rod cells in the retina
• Reproduction: Spermatogenesis in male
• Growth: Required for bone growth to keep pace with CNS growth
• Differentiation: Normal differentiation of epithelial cells

Question 10

What results from Vitamin A deficiency?

Answer 10

Deficiency – concentrations of less than 0.5 μmol/L causes

• Night blindness
• Xerophthalmia (Xerophthalmia is a medical condition in which the eye fails to produce tears)
• Blindness

Rare in affluent countries due to liver stores. May be leading cause of preventable blindeness in children. Plasma levels may not be indicative of total body deficiency. May not decrease until liver depleted

Question 11

What are the worries with excess viramin A?

Answer 11

• Hypervitaminosis A
• Acute (short term) toxicity may lead to nausea, vomiting, severe headaches, dizziness, fatigue, irritability, dry skin and cerebral oedema
• Chronic (long term) toxicity from moderately high doses may lead to dry skin, joint and bone pain, dry lips, anorexia, psychiatric changes and cerebral oedema
• Severe toxicity can lead to eye and liver damage

Question 12

What should be done with Vitamin A during pregnancy?

Answer 12

Limit Vitamin A when pregnant as it is a teratogen

Question 13

What is Carotinaemia?

Answer 13

• Reversible yellowing of skin
• Does not cause toxicity as its metabolic conversion is regulated by vitamin A status

Question 14

How is Vitamin A investigated?

Answer 14

• Assessed by measuring serum/plasma retinol
• HPLC with UV, electrochemical or mass spectrometry detection
• Reference method: Gas chromatography-isotope dilution mass spectrometry
• Protect sample from light to prevent false increase in concentration
• Retinol binding protein and transthyretin may also be measured

Question 15

What are forms of Vitamin D?

Answer 15

• Vitamins D2 (ergocalciferol)
• Vitamin D3 (cholecalciferol)
• Active form is 1,25 (OH)2 Vitamin D which binds to nuclear vitamin D

Question 16

What are sources of Vitamin D?

Answer 16

• Fish
• Eggs
• Milk

Question 17

What are the functions of Vitamin D?

Answer 17

Regulation of Calcium and Phosphate:

• Increases intestinal absorption of Calcium
• Resorption and formation of bone, via PTH
• Reduces renal excretion of Calcium

Question 18

How does Vitamin D increase the intestinal absoprtion of calcium and phosphate?

Answer 18

• Small intestine absorbs 10-15% dietary calcium in low vitamin D state. Rises to 30-40% with adequate vitamin D
• Low calcium absorption can lead to increased PTH (surrogate marker)

Question 19

What are the effects of deficeincy of Vitamin D?

Answer 19

• Rickets in Children
• Osteomalacia in Adults. Characterised by incomplete mineralisation of the underlying mature organic bone matrix (osteoid)

Question 20

What are the effects of excess in Vitamin D?

Answer 20

• Early symptoms are GI related: anorexia, diarrhoea, nausea, vomiting
• Bone pain, headaches, muscle and joint pain, excessive thirst, weakness, nervousness, itching, kidney stones. Hypercalcaemia is responsible for most symptoms seen with vitamin D toxicity

Toxicity defined by institute of medicine as >500 nmol/L 25(OH)vitamin D in the short term.

Long term optimal level of 50 – 100 nmol/L

Question 21

What are investigations for Vitamin D?

Answer 21

Reference method:

• Isotope dilution liquid chromatography tandem mass spectrometry

Routine methods:

1. Immunoassay
   
   • Cheap, quick and automated
   • Must measure total vitamin D (i.e. vitamin D2 and vitamin D3)
2. Liquid chromatography-mass spectrometry (LCMS)
   
   • Allows separation of vitamin D2 and D3
   • More expensive and labour intensive
   • Used for 1,25(OH)2 Vitamin D

Question 22

Which forms of Vitamin D are looked at in the investigations?

Answer 22

• Status is assessed by measuring the major storage forms 25-hydroxyvitamin D3 and D2.
• Bound to vitamin D binding protein and albumin in plasma. Also, C-3 epimer in infants. Requires extraction step for measurement.
• 1,25(OH)2 Vitamin D can also be measured but this is rarely required in practice (pmol/L quantities)

Question 23

What are deatures of Vitamin E?

Answer 23

• 8 compounds - α-tocopherol is the main form
• ​Liver takes up vitamin E after the various compounds have been absorbed in small intestine

Question 24

How do Lipids in Serum affect the Vitamin E?

Answer 24

• Vitamin E is bound to low density β-lipoproteins and pre-albumin in plasma.
• If concentration of lipid in serum rises, vitamin E will move from cell membrane to bind to lipoproteins in serum.
• May result in an elevated vitamin E and can mask deficiency. May determine vitamin E expressed in relation to lipids

Question 25

What are functions of Vitamin E?

Answer 25

* Anti-oxidant protecting cells from free radicals * Protects unsaturated fatty acids against free radical mediated oxidation * Protects cell membranes * Involved in immune function * May protect against cardiovascular disease * Inhibits activity of PKC which is involved in cell proliferation and differentiation in smooth muscle cells, platelets and monocytes

Question 26

What are 3 groups that could become deficient in Vitamin E?

Answer 26

* Fat malabsorption e.g. Cystic Fibrosis * Premature, very low birth weight infants (poor placental transport) * Rare congenital disorders of fat metabolism e.g. Abetalipoproteinemia

Question 27

What are signs of Vitamin E deficiency?

Answer 27

* Haemolytic anaemia due to the shortened lifespan of erythrocytes with fragile membranes which not respond to iron therapy * Myopathy * Retinopathy * Ataxia * Neuropathy

Question 28

What are consequences of excess in Vitamin E?

Answer 28

* Low toxicity * High intakes may impair absorption of other fat-soluble vitamins * Can therefore result in vitamin K deficiency and consequently bleeding problems * Taking large doses in conjunction with anticoagulant or antiplatelet medication such as warfarin can increase risk of bleeding

Question 29

What are forms of Vitamin K?

Answer 29

* **Vitamin K1 (phylloquinone):** Synthesized by plants and present in food. Carried in Chylomicrons * **Vitamin K2 (menaquinone):** Synthesized in humans by intestinal bacteria * **Synthetic vitamin K’s: K3 (menadione) & K4 (menadiol)**

Question 30

What are the functions of Vitamin K?

Answer 30

* Promotes blood clotting and is required for the conversion of several clotting factors and prothrombin * Necessary for liver synthesis of plasma clotting factors II, VII, IX and X.

Question 31

What happens with Vitamin K deficiency?

Answer 31

* Rare in adults, unless on warfarin. Can also occur with fat malabsorption * Haemorrhagic disease of the newborn develops readily. Intestinal flora isn’t become established within the first week of birth * Early breast milk is low in vitamin K

Question 32

What are consequences of Vitamin K excess?

Answer 32

**Vitamin K1 is relatively safe and up to 1mg/day unlikely to result in adverse effects** **Synthetic forms, particularly water-soluble Vitamin K3 are more toxic** * High doses result in oxidative damage, red cell fragility, formation of methaemoglobin * In premature infants, this has caused liver problems and brain damage

Question 33

What are investigations for Vitamin K

Answer 33

* Vitamin K concentration is influenced by plasma triglyceride concentration due to association with VLDL * May be reported as a ratio. Can be measured directly using HPLC with fluorimetric detection * Can be measured indirectly by prothrombin time (INR)

Question 34

What are features of Vitamin C?

Answer 34

* Humans are unable to synthesise vitamin C endogenously * There are higher requirements in diets devoid of fresh fruits & vegetables and in smokers, Pregnancy, post-operative patients * Circulates bound to albumin

Question 35

What are fucntions of Vitamin C?

Answer 35

**Collagen Synthesis** * Cofactor for hydroxylation of proline & lysine residues during synthesis of collagen. * Without hydroxylation, collagen cannot form a triple helix and lacks tensile strength. **Antioxidant** * Regenerates other antioxidants e.g. vitamin E **Iron absorption** * Facilitates intestinal absorption of dietary non-haem Fe by keeping it in the Fe2+ state

Question 36

What does Vitamin C deficiency cause?

Answer 36

Leads to Scurvy * Easy bruising and bleeding, teeth and gum disease, hair loss * Scurvy is treated with vitamin C supplements. It quickly improves symptoms. * Some symptoms, such as joint pain, will usually resolve within 48 hours. Most people will make a full recovery within two weeks.

Question 37

What odes Vitamin C excess lead to?

Answer 37

* Doses \>1g/day can cause GI side effects * Possible increase in oxalate excretion and increased risk of renal stones * Promotes iron overload in patients with thalassemia or hemochromatosis * No evidence that increased vitamin C reduces the incidence or duration of colds

Question 38

What is the Rebound effect in Vitamin C excess?

Answer 38

* Prolonged high intakes of vitamin C increases rate of turnover so sudden cessation can result in rebound deficiency. * People who take Vitamin C supplements at high doses should be advised not to take them for prolonged periods, and then to reduce the level of intake gradually

Question 39

What are investigations for Vitamin C?

Answer 39

* Can be measured in plasma but unreliable in the acute phase response * Affected by recent intake * Measured by HPLC with fluorimetric detection * Samples very unstable, must be treated with metaphosphoric acid and frozen

Question 40

What are the B vitamins?

Answer 40

* Thiamine (vitamin B1) * Riboflavin (vitamin B2) * Niacin (vitamin B3) * Pantothenic acid (vitamin B5) * Vitamin B6 * Biotin (vitamin B7) * Folic acid (vitamin B9) * Vitamin B12

Question 41

What are features of Vitamin B1?

Answer 41

* Active form is (TPP). * Main circulating form of vitamin B1 is thiamin diphosphate (TDP). * It is mainly found in red blood cells (\>90%) * Coenzyme for small number of enzymes which are critical in the catabolism of amino acids and carbohydrates e.g. Transketolase, Pyruvate dehydrogenase * Required for ATP production

Question 42

What are causes of Vitamin B1 deficiency?

Answer 42

* **Primary:** Found in areas where polished rice or refined carbohydrates is the major part of diet * **Secondary:** Alcoholics (decreased intake), pregnancy, lactation, hyperthyroidism, fever (increased demand)

Question 43

How is Subclinical Thiamine Deficiency detected?

Answer 43

* Subclinical thiamine deficiency can be unmasked in malnourished patients given IV glucose due to increased metabolic requirements for the vitamin. * Alcoholic and others at risk must receive IV thiamine 100mg before receiving IV glucose solutions

Question 44

What are the effects of deficiency in Vitamin B1?

Answer 44

**Beriberi** * Neuropathy, burning feet, decreased sensation, muscle pain, muscle weakness, epileptic fits * Cardiac symptoms (wet beriberi) - heart failure **Wernicke’s encephalopathy & Korsakoff’s Psychosis** * Cerebral - most sufferers are alcoholics

Question 45

What are investigations for Vitamin B1?

Answer 45

* Can be measured directly from whole blood sample using HPLC with fluorimetric detection * Transketolase activation assay as an indirect measurement of status

Question 46

What are the functions of Vitamin B2?

Answer 46

* Usually found as part of FAD (flavine adenine dinucleotide) and FMN (flavine adenine mononucleotide) * Involved with many enzymes which catalyse redox reactions. FAD is part of the electron transfer chain * Also involved with enzymes which work with cytochrome P450, a system which metabolises many drugs and toxins

Question 47

What are the effets in Vitamin B2 deficiency?

Answer 47

* Rarely seen in isolation * Symptoms include sore throat, sore tongue, sore mouth, sore corners of lips * Alcoholics are at risk, as are lactose-intolerant people, who avoid dairy products

Question 48

How does vitamin B2 found in plasma and how is it investigated?

Answer 48

* Vitamin B2 is bound to albumin in plasma. Albumin is a negative acute phase reactant so concentrations of Vitamin B2 therefore fall in acute phase * Measured in whole blood/packed red cells * HPLC with fluorimetric detection

Question 49

What are functions of Vitamin B3?

Answer 49

* Used to make NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate) * Coenzymes to more than 200 enzymes which are involved in redox reactions * In high doses, has been used to treat CVD risk: ↓ Lp(a), ↑ HDL-cholesterol, ↓ triglycerides

Question 50

What odes deficiency of Vitamin B3 cause?

Answer 50

Pellagra -3 Ds * Diarrhoea * Dementia * Dermatitis Tryptophan can be used by the liver to synthesise niacin, * Conditions such as Hartnup disease (deficient tryptophan absorption), carcinoid (↑ need for tryptophan to make 5HT) and isoniazid (used to treat TB) can result in pellagra

Question 51

What are functions of Vitamin B5?

Answer 51

* Required to synthesise coenzyme A along with metabolism and synthesis of fats, proteins and glucose

Question 52

What does deficiency of Vitamin B5 lead to?

Answer 52

* Very rare in isolation, but can lead to lack of energy * Tingling feet * Parasthesia * Muscle cramps

Question 53

What are forms for Vitamin B6?

Answer 53

* Main forms are Pyridoxal (PL) and pyridoxal 5’ phosphate (PLP) * PLP is the functional form * Bound to albumin in plasma and albumin is a negative acute phase reactant so PLP concentrations can therefore fall in acute phase

Question 54

What are functions of Vitamin B6?

Answer 54

Co-enzyme in many enzymatic reactions in metabolism: * PLP co-factor for amino acid metabolism: transamination, deamination, and decarboxylation * Conversion of tryptophan to niacin * Release of glucose from glycogen, haem synthesis * Synthesis of neurotransmitters e.g. serotonin

Question 55

What are the effects of Vitamin B6 deficiency?

Answer 55

* Pellagra-like syndrome, with seborrheic dermatitis, glossitis, and cheilosis * Depression, confusion, EEG abnormalities, and seizures. Seizures, particularly in infants, may be refractory to treatment with anticonvulsants * Normocytic, microcytic, or sideroblastic anemia can also develop.

Question 56

What are causes of Vitamin B6 deficiency?

Answer 56

* Inadequate intake (alcoholics) * Pyridoxine-inactivating drugs (e.g. anticonvulsants, isoniazid) * Isoniazid can induce B6 deficiency by forming an inactive derivative with pyridoxal phosphate * B6 supplement is thus an adjunct to isoniazid treatment

Question 57

What are investigations for Vitamin B6 deficeincy?

Answer 57

Generally, measure PLP only, but can also measure pyridoxic acid and pyridoxal. This is especially useful in the diagnosis of hypophosphatasia * Low levels of Akaline phosphatase * Elevated PLP * Low plasma PA Measured in whole blood/red cells by HPLC with fluorimetric detection

Question 58

What is the fucnion of Viamin B7?

Answer 58

* Required for cell growth, fat and amino acid metabolism * Cofactor for carbon dioxide transfer in several carboxylase enzymes

Question 59

What leads to Vitamin B7 deficiency?

Answer 59

* Rare as gut flora produce biotin in excess of daily requirements * Number of metabolic disorders where problems with biotin use

Question 60

What are functions of Vitamin B9?

Answer 60

* Coenzyme in methylation reactions, DNA synthesis, synthesis of methionine from homocysteine. * Higher requirements in pregnancy.

Question 61

What are causes of Vitamin B9 deficiency?

Answer 61

* Malabsorption * Use of drugs that interfere with folic acid metabolism (anticonvulsants, methotrexate) * Disease states which increase cell turnover (e.g. leukaemia, haemolytic anaemias, psoriasis)

Question 62

What are symptoms of Vitamin B9 deficiency?

Answer 62

* ↑ Homocysteine levels (a correlate with ↑ cardiovascular disease risk) seen * Macrocytic anaemia which can lead to lethargy and weakness * Foetal developmental abnormities: neural tube defects (anencephaly, spina bifida)

Question 63

What are functions of Viitamin B12?

Answer 63

* Important role in metabolism of carbohydrates, proteins and lipids * Essential role in blood cell production in bone marrow * Unlike most water-soluble vitamins, B12 can be stored in liver

Question 64

What are causes of Vitamin B12 deficiency?

Answer 64

* **Pernicious anaemia:** autoimmune destruction of IF-producing cells in stomach. Needs intrinsic factor produced by stomach for absorption. IF-B12 complex absorbed in terminal ileum * **Malabsorption:** lack of stomach acid (atrophic gastritis, drugs which inhibit acid-production), pancreatic disease, small bowel disease * **↓ methionine synthase activity traps folate in an inactive form, leading to symptoms of folic acid deficiency:** macrocytic anaemia. * **Vegan diet**