Clinical Chem Vitamins & Minerals

Learning Outcome

  • To understand the roles of vitamins and minerals important to human health
  • To understand the impact on human health due to deficiency of important vitamins and minerals

Micronutrients

Macronutrients

  • made up the bulk of the nutrition in food, i.e., carbohydrates, fats, and proteins
  • supply calories and act as the building blocks for muscles and tissues

Micronutrients are….

  • essential dietary components for the maintenance of health
    • deficiency can cause severe and life-threatening clinical disorders
  • disproportionately common in low- and middle-income countries
  • mostly preventable through
    • nutrient education
    • consumption of healthy diet
    • food fornication and supplementation

Fat-soluble vitamins

  • Lipophilic, hydrophobic molecules
  • incorporated into mixed micelles to be absorbed from intestine lume
  • upon absorption, the fat soluble vitamins are incorporated into chylomicrons
    • transport via the lymph into peripheral blood circulation
    • stored in the liver and adipose tissues
  • deficiencies occur with the malabsorption of fat

Vitamin A

  • mainly consists of retinol and retinyl esters
  • Two sources:
    • performed vitamin A (aka retinol and retinyl esters)
    • diary products, eggs, fish and liver
    • provitamin A carotenoids (beta-carotene)
    • green leafy vegetables, carrots and cantaloupe
  • physiological roles:
    • vision
    • maintain healthy cell-mediated immunity
    • differentiation of certain tissues
    • morphogenesis in developing embryos
  • deficiency
    • still common in developing countries due to poverty or traditional diets
    • night blindness, conjunctival keratosis, degeneration of cornea
    • abnormal lung development, respiratory diseases, anaemia and severe infection
  • Excess
    • acute vitamin A toxicity (hypervitaminosis)
    • severe headache, blurred vision, nausea, dizziness, aching muscles, coordination problems
    • chronic hypervitaminosis
    • dry skin, painful muscles and joints, fatigue, depression

Vitamin D (calciferol)

  • Two forms: vitamin D2, vitamin D3

  • Sources:

    • naturally found in certain food, e.g., salmon, mackerel, sardines & mushrooms
    • fortified milk, fortified cereal and fortified juice, dietary supplement
    • produced endogenously in the skin when exposed to direct sunlight
  • Activation of vitamin D

    • biologically inert and must undergo two hydrocylation steps for activation

  • Physiological roles:

    • promote calcium absorption in the intestines
    • maintain normal bone mineralisation & prevent hypocalcemia
    • bone growth and bone remodelling
    • regulate genes involved in cell proliferation, differentiation and apoptosis
    • reduce inflammation
    • modulate cell growth, neuromuscular & immune function and glucose metabolism
  • serum concentration of 25 (OH)D → assess the vitamin D status

Vitamin D deficiency

  • Causes:
    • limited exposure to sunlight
    • low intake
    • failure of kidneys to convert 25(OH)D to its active form
    • inadequate vitamin D absorption
    • drugs
    • chronic diseases
  • Clinical manifestations
    • rickets in children → soft bones & skeletal deformities
    • severe rickets cases → failur to thrive, developemtnal delay, hypocalcemic seizures, tetanic spasms, cardiomyopathy & dental abnormalities
    • osteomalacia in adolescents & adults
    • inadequate bone mineralisation during remodeling process
    • bone deformities, pain, hypocalcemic seizures, tetanic spasms & dental abnormalities

Vitamin E (alpha-tocopherol)

  • exists in 8 naturally occurring plant rocopherols and tocotrienols
    • alpha-, beta-, gamma-, and delta-tocopherol
    • alpha-, beta-, gamma-, and delta-tocotrienol
  • alpha-tocopherol is the only biologically active form in human
  • sources:
    • plants oil, almonds, peanuts, leafy greens, poultry, eggs, dairy, fortified cereals, oral supplement in capsule or drops
  • physiological roles:
    • important to vision, reproduction and the health of blood, brain and skin
    • as an antioxidant and free radicals scavenger
    • protect cells from damaging effects of free radicals
    • maintain integrity of all cell membranes

Vitamin E deficiency

  • Rare; could be found in premature babies of very low birth rate
  • oxidative destruction of membrane phospholipids, e.g.,
    • red blood cell fragility leading to haemolytic anemia
    • neuronal degeneration leading to peripheral neuropathies
  • genetic abnormalities associated with vitamin E metabolism
  1. abetalipoproteinemia

    1. poor absorption of dietary fat

      1. inadequate vitamin E delivery to tissues
      2. poor transmission of nerve impulses, muscle weakness, retinal degeneration
  2. Friedreich type of spinocerebellar ataxia

    1. defects in hepatic alpha-tocopherol transferase

      1. develop nerve damage, lose the ability to walk

Vitamin K

  • Vitamin K1; Vitamin K2
  • Phylloquinone
    • present primarily in green leafy vegetables
    • main dietary form of vitamin L
  • Menaquinones
    • predominantly bacterial origin
    • present in modest amount in animal-based or fermented foods
  • Sources:
    • green leafy vegetables
    • vegetable oils
    • cereals
    • others such as meat, fish & dairy products
    • can be synthesised by Gram-positive bacteria in the jejunum & ileum
  • Physiological roles
    • act as coenzyme for vitamin K-dependent carboxylase involved in the post-translational y-carboxylation of proteins
    • increase the capacity of proteins to bind to calcium
      • procoagulant proteins of the clotting cascade
      • anticoagulant proteins
      • bone matrix proteins
      • proteins of the renal epithelium

Deficiency of Vit K

  • Clinical manifestation
    • bleeding and haemorrhage
    • reduce bone mineralisation → osteoporosis
  • newborns are more susceptible due to
    • low placental transfer of vit k
    • lack of vit k in breast milk
    • bacterial flora not yet established
  • adults limited to malabsorption disorder or drugs that interfere with vit k metabolism