Nutrition 3

• The body absorbs fat-soluble vitamins into newly forming micelles in the small intestine

  
• Absorption of fat-soluble vitamins

  1. Absorption into enterocytes

  2. Packaging into chylomicrons

  3. Secretion into lymphatic system

  4. Entry into bloodstream

  
• Chylomicrons are metabolized by lipoprotein lipase, which causes the release of fat-soluble vitamins into tissues for use and storage

  
• Fat-soluble vitamins are retained by the body for a longer time than the water-soluble vitamins

  
• Vitamin A


  Also known as retinol

  
• Retinol


  Used to synthesize retinal
• Vitamin A


  • Plays an integral role in the differentiation and proliferation of epithelial cells in the eyes, salivary glands, and genitourinary tract
  • A precursor to the nuclear hormone all-trans retinoic acid, which heterodimerizes with retinoic acid receptors (RAR) in the nucleus
  • RAR-retinoid X receptor heterodimers serve as transcription factors that bind certain elements in promoters of genes which encode important structural proteins, extracellular matrix proteins, and enzymes throughout the body
  • Stimulates T-lymphocyte differentiation and B-lymphocyte activation in response to immune stimuli

  
• Xerophthalmia


  The clinical spectrum of ocular manifestations of vitamin A deficiency
• Serum retinol levels reflect liver vitamin A stores when they are severely depleted or extremely high; however, between these extremes, plasma or serum retinol is homeostatically controlled and hence may not correlate well with vitamin A intake

  
• Vitamin A deficiency


  • Keratomalacia
  • Follicular hyperkeratosis: keratin deposits form around hair follicles; causes rough texture to the skin resembling 'goose flesh; facial skin scaly, off-colour, cracked, or dry to the point of flaking
• Vitamin D


  A collective term used to refer to any one of 4 similar substances, only one of which has biological activity: ergocalciferol (D2 from plants); cholecalciferol (D3 from animals); 25-hydroxyvitamin D (circulating form); 1,25-dihydroxyvitamin D (calcitriol, active form)

  
• Required Dietary Allowance for Vitamin D

  Children: 10 micrograms/day (400 IU); Adults: 20 micrograms/day (800 IU); Pregnancy and lactation: 25 micrograms/day (1000)

  
• Vitamin D deficiency


  • In children causes rickets
  • In adults causes osteomalacia

  
• Vitamin E


  • Potent antioxidant that prevents oxidation of fatty acids
  • Protects lipids in membranes from oxidative damage: particularly phospholipids of mitochondria and endoplasmic reticulum, which are more unsaturated; cell membranes of lung, brain, and erythrocytes also susceptible
  • Protects erythrocytes from hemolysis by oxidising agents

  
• Functions of Vitamin K

  • Cofactor for the enzyme, γ-glutamylcarboxylase, which catalyzes the carboxylation of the glutamic acid to γ-carboxyglutamic acid
  • Vitamin K-dependent γ-carboxylation that occurs only on specific glutamic acid residues in identified vitamin K-dependent proteins (VKDP) is critical for their ability to bind calcium
  • The ability to bind Ca2+ is required for the activation of the several vitamin K-dependent clotting factors in the coagulation cascade

  
• Vitamin K deficiency


  • Risk factors: antibiotic use, nutritional deficiency, and high ingestion of vitamins A and E
  • Newborns are at risk for deficiency due to immature gut flora, poor placental transfer, and low content in breast milk
  • A common clinical syndrome that results from vitamin-K deficiency is a hemorrhagic disease of the newborn
  • In adults, deficiency can cause easy bleeding and bruising

  
• Vitamin C


  Exists in reduced [ascorbate] and oxidized forms as dehydroascorbic acid which are easily inter-convertible and biologically active thus it acts as important antioxidant

  
• Vitamin C is easily oxidized and destroyed by oxygen, alkali and high temperature
• Most of the plant and animal species have the ability to synthesize vitamin C from glucose and galactose through uronic acid pathway but humans and other primates cannot do so because of deficiency of enzyme gulonolactone oxidase

  
• Functions of Vitamin C

  • Helps in the synthesis and metabolism of tyrosine, folic acid and tryptophan, hydroxylation of glycine, proline, lysine carnitine and catecholamine
  • Facilitates the conversion of cholesterol into bile acids and hence lowers blood cholesterol levels
  • Increases the absorption of iron in the gut by reducing ferric to ferrous state
  • As an antioxidant, it protects the body from various deleterious effects of free radicals, pollutants and toxins
  • Biochemical functions are largely dependent on the oxido-reduction properties of l-AA which is a co-factor for hydroxylation and activity of mono-oxygenase enzymes in the synthesis of collagen, carnitine and neurotransmitters
  • Accelerates hydroxylation reactions by maintaining the active centre of metal ions in a reduced state for optimal activity of enzymes hydroxylase and oxygenase. Thus, it is crucial in the maintenance of collagen which represents about one-third of the total body protein
  • A co-factor for the enzyme dopamine-β-hydroxylase, which catalyzes the conversion of neurotransmitter dopamine to norepinephrine and hence essential for the synthesis of catecholamines
  • Catalyzes other enzymatic reactions involving amidation necessary for maximal activity of hormones oxytocin, vasopressin, cholecystokinin and alpha-melanotropin
  • Involved in the transformation of cholesterol to bile acids as it modulates the microsomal 7α-hydroxylation, the rate limiting reaction of cholesterol catabolism in liver

  
• Required Dietary Allowance for Vitamin C

  Adults: 60 mg/day; Children: 40 mg/day

  
• Vitamin C deficiency


  • Severe vitamin C deficiency causes scurvy
  • Adults feel tired, weak, and irritable if their diet is low in vitamin C. They may lose weight and have vague muscle and joint aches
  • The symptoms of scurvy develop after a few months of deficiency. Bleeding may occur under the skin (particularly around hair follicles or as bruises), around the gums, and into the joints. The gums become swollen, purple, and spongy. The teeth eventually loosen. The hair becomes dry, brittle, and coiled (like a corkscrew), and the skin becomes dry, rough, and scaly. Fluid may accumulate in the legs. Anemia may develop. Infections may develop, and wounds do not heal
  • Infants may be irritable, have pain when they move, and lose their appetite. Infants do not gain weight as they normally do. In infants and children, bone growth is impaired, and bleeding and anemia may occur

  
• Major (or macrominerals)


  Generally required in larger amounts. Some examples include calcium, phosphorus, potassium, sulphur, sodium, chloride, magnesium
• Trace minerals (microminerals)


  Although equally important to bodily functions are required in smaller amounts. Examples include iron, zinc, copper, manganese, and iodine selenium
• Functions of minerals


  • Co-factors of enzymes
  • Electrolytes
  • Structure of tissues such as: bones, teeth, nails, blood, nerves cells, and muscles
• Calcium


  • Most abundant mineral
  • 99% of the body's Ca exists in bones and teeth: provide structure and strength; serve as a reserve bank that can release Ca when blood level drops
  • 1% of Ca in fluids that bathe and fill cells
• Functions of Calcium


  • Regulation of ion transport
  • Maintenance of blood pressure
  • Blood clotting
  • Muscle contraction
  • Secretion of hormones, digestive enzymes, and neurotransmitters
  • Activation of cellular enzymes
• Hypocalcemia


  • Low blood Ca causes tetany, characterised by: paresthesias (tingling, burning, pricking, or numbness) of the lips, tongue, fingers and feet; carpopedal spasm, which may be prolonged and painful; generalised muscle aching; spasms of facial musculature
  • Although Ca is typically measured in labs from blood plasma, tetany is caused by low ionic Ca in extracellular and intracellular fluid
• Bone loss is an inevitable consequence of ageing. It can be reduced by a good diet and exercise
• Obtaining enough Ca in childhood helps ensures the skeleton starts adulthood with a high bone density
• Osteoporosis, or adult bone loss, occurs if a person's Ca bank is not sufficient
• A diet low in Ca during the growing years may prevent the achievement of peak bone mass
• Phosphorus


  • 85% of body's phosphorus found combined with Ca in bones and teeth
  • Phosphorus also: helps maintain acid-base balance; is part of nucleic acids (DNA, RNA); involved in energy metabolism (ATP, GTP); is part of cell membranes (phospholipids)

  
• Phosphorus deficiency


  • A phosphorus deficiency is called hypophosphatemia, defined by blood levels that fall below the normal range
  • The most common causes of deficiency are kidney problems or a condition called hyperparathyroidism, in which too much parathyroid hormone is released that causes phosphorus to exit the body through urine. Also, the overuse of aluminum-containing antacids can bind to phosphorus and increase the risk of a deficiency
  • A notable but less common occurrence of hypophosphatemia occurs with refeeding syndrome, seen in people with severe malnutrition. Symptoms appearing with a phosphorus deficiency: poor appetite, anemia, muscle weakness, bone pain, bone disease (osteomalacia, rickets), confusion, increased susceptibility to infections
• Magnesium


  • Naturally present in a variety of foods, available as a supplement, and an ingredient in antacids and laxatives
  • Plays an important role in assisting more than 300 enzymes to carry out various chemical reactions in the body such as building proteins and strong bones, and regulating blood sugar, blood pressure, and muscle and nerve functions
  • Acts an electrical conductor that contracts muscles and makes the heart beat steadily
  • More than half of the magnesium in our body is stored in bones, and the remaining in various tissues throughout the body
• Functions of Magnesium


  • Acts as an activator of many enzymes especially those involving transfer of phosphate groups from ATP such as: hexokinase; phosphofructokinase
  • Mg also activates a number of enzymes such as: enolase; glucose-6-P dehydrogenase; pyruvate carboxylase; thiokinase; glucose 6 phosphogluconate dehydrogenase
• Sources of Magnesium


  • Whole grains
  • Nuts
  • Legumes
  • Leafy green vegetables
  • Milk and yogurt
• Magnesium deficiency


  • Although magnesium is naturally found in a variety of foods and some fortified foods, many people eat less than recommended amounts
  • However, these deficiency levels are marginal and not likely to produce symptoms
  • The body also helps to preserve magnesium levels when stores are low by limiting the amount excreted in urine and absorbing more magnesium in the gut
  • A true deficiency occurs with a long-term low magnesium diet, malabsorption, and large losses from alcohol abuse or use of medications that deplete magnesium (some diuretics, proton pump inhibitors, and antibiotics)
  • Signs of deficiency include: fatigue, weakness, poor appetite, nausea, vomiting, numbness or tingling in skin, muscle cramps, seizures, abnormal heart rate
• Sodium


  • The major cation of the extracellular fluid
  • Roles: maintenance of electrolyte balance of body fluid; essential for nerve transmission; involved in active transport of glucose, galactose, and amino acids across intestinal mucosa
  • 30 to 40 % of body's Na on surface of bone crystals where it is easily drawn upon to replenish blood concentrations

  
• Chloride


  • Helps to regulate the amount of fluid and types of nutrients going in and out of the cells
  • Absorbed in the small intestine and remains in the body's fluids and blood. Any excess amount is excreted in urine. Chloride is usually bound to sodium, and therefore the amount in blood tends to coincide with sodium levels