T1 L9: Micronutrients and trace elements

• What are the importance of vitamins?

  they act as coenzymes in metabolic pathways
• What is the food matrix?

  well organised structure of fresh food products consisting vacuole, cytoplasm, cell wall, intercellular spaces
• What is bioavailability in relation to nutrients?

  ability of nutrients to interact with the body to be absorbed
• What is the pattern of micronutrient deficiency in the UK like?

  generally population well nourished

  but increasing concerns about marginalised / minority groups, very young/very old associated with:

  1. Poor dietary intake
  2. Excessive energy-dense / nutrient-light diets
  3. Extreme diets/chronic dieting (removal of one or more food groups)
  4. Reduced bio-availability
• What is the evidence of micronutrient deficiency in UK?

  • iron deficient anaemia (low Hb) & low iron stores (plasma ferritin) in adult women and older girls
  • low vitamin D in adults and older children both male and female. implications for bone health
  • substantial proportion of adults and older children have low functional riboflavin (B2) status
• Micronutrient deficiencies are associated with illness and age.
• What conditions are associated with these micronutrient deficiencies?

  alcohol liver disease - thiamine (B1), vitamin D

  inflammatory bowel disease - iron, B12, vitamin D, vitamin K, folic acid, selenium, zinc, vitamin B6, vitamin B1

  obesity - vitamin D, copper, zinc

  fat malabsorption - A, D, E, K

  high output stomas - sodium loss approx 100mmol/L, risk of low magnesium

  Old age - Vit B12

  Fraility/housebound - Vit D
• What vitamins do humans require?

  13 in total:

  • 4 fat-soluble (A, D, E, K)
  • 9 water soluble: vitamin C + 8 B vitamins

  dosage vary from microgram to mgs

  excessive intake can be toxic
• What are the 9 water soluble vitamins?

  Vitamin C

  B1 (thiamine)

  B2 (riboflavin)

  B3 (niacin)

  B5 (pantothenic acid)

  B6 (pyridoxine)

  B7 (biotin)

  B9 (folate)

  B12 (cobalamin)
• What are the 4 fat soluble vitamins?

  A, D, E, K
• What is the significance of vitamin C in humans?

  co-factor in posttranslational formation of amino acid hydroxyproline in collagens & other proteins

  also involved in:

  • tyrosine metabolism
  • CHO metabolism
  • lipid and protein synthesis
  • iron metabolism
  • resistance to infections
  • cellular respiration
  • conversion of folic acid -> folinic acid
• What is scurvy?

  Vitamin C deficiency
• What is the significance of B vitamins?

  metabolism

  act as co-enzymes in many metabolic processes eg respiration

  hence vitamin B deficiency ususally manifests as lack of energy/tiredness
• What are the characteristics of Vitamin B1 (thiamine)?

  site of absorption: jejunum and ileum

  important in memory formation

  deficiency in people who consume high amounts of alcohol

  can develop Wernicke Korsakoff syndrome
• What is Wernicke Korsakoff syndrome and how does it relate to micronutrients?

  irreversible structural changes to the frontal lobe of brain

  difficulties forming memories

  due to thiamine (vitamin B1) deficiency
• What are the characteristics of Vitamin B2 (riboflavin) absorption?

  2 stage process of absorption in small intestine:

  1. released from proteins/proteolytic enzymes
  2. hydrolysed by brush border enzymes

  so any defect in enzyme release from pancreas can have an effect on riboflavin absorption
• What are the characteristics of Vitamin B12?

  synthesised by microorganisms in animals

  absorbed by distal (end of ) ileum
• What is the mechanism of absorption of Vitamin B12 (cobalamin)?

  B12 in proteins -> HCl + pepsin release B12 -> bind with Haptocorrin (HC)/Transcobalamin (TC)/ R factor -> jejunum -> B12 released from HC/TC -> bind intrinsic factor -> IF complex bind receptors at distal ileum -> B12 slowly absorbed
• What is pernicious anaemia?

  Vitamin B12 deficiency
• What is the link between Vitamin B12 and folate?

  a high folate intake can mask vitamin B12 deficiency until its neurological effects become irreversible
• What can the deficiencies in both B12 and folate result in?

  increased levels of homocysteine (amino acid)

  increase risk for dementia, heart disease, stroke
• What is the significance of Vitamin A?

  vitamin A deficiency major cause of blindness worldwide

  carotenes solubilised into micelles, absorbed through membrane and converted to retinol
• What is the significance of Vitamin D?

  two forms:

  • Vitamin D2 (dietary)
  • Vitamin D3 (UV light)

  needs to be activated by kidney

  role in immunity
• What are some factors that have an impact on vitamin D bioavailability?

  vegan/vegeterian diet

  use of medication:

  • eg anticonvulsants, rifampicin, cholestyramine, anti-retrovirals
• What is the mechanism of Calcium absorption?

  20-30% absorbed in acid medium

  • When intake low and requirement high: Vitamin D-dependent calcium transport system in duodenum
  • When intake high: passive process in jejunum
• What are the 2 proposed mechanisms of Calcium absorption?

  1. Paracellular
  2. Transcellular - bound to calbindin-D

  
• What are the properties of Iron?

  always exists bound to a protein - free iron is toxic

  two forms:

  • haem iron (animal food), easiest to absorb
  • non-haem iron (plant food)

  all iron convered to ferrous Fe2+ form prior to absorption through DMT1 channels

  iron transferred to circulation from intestinal epithelium via ferroportin 1
• What is the mechanism of iron transport?

  DMT1 channels -> iron converted to ferrous form (Fe2+) -> intestinal epithelium -> ferroportin-1 -> circulation -> plasma -> transport in blood -> transferrin receptors in target cell (TfR) -> receptor-mediated endocytosis -> enter cells