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