Micronutrients & Malnutrition Flashcards
Iron - Functions and Distribution
Total body iron ~5g
50% as circulating hemoglobin, 50% stored
Functions: O2 transport in blood and muscle, electron transport, activation of O2 (oxidases)
Iron - Sources
Heme: Meats, liver; low in all milks
Non-heme: Plant sources (legumes, whole grains, nuts), fortified foods (cereals, grains)
Iron - Absorption / Bioavailability
Heme iron from animals is absorbed > non-heme iron from plants; insoluble complexes in plants (phytate, polyphenols) interfere with absorption of non-heme iron
Fe is absorbed better in the reduced state (Fe2+); ascorbic acid increases absorption by affecting redox state
Phytic Acid
Storage form of phosphorous in plants; contains 6 negatively charged phosphate groups which can bind cations in the gut lumen, reducing absorption of these ions (Zn, Fe, Ca); humans don’t have phytases
High in grains (maize, wheat), legumes; globally, a major cause of dietary Zn and Fe deficiencies
Iron - homeostasis
Absorption is the main point of regulation; absorption is increased in iron deficiency, decreased in inflammation due to increased hepcidin release from hepatocytes (hepcidin blocks iron absorption)
Loss - bleeding, cell sloughing
Stored by ferritin in liver, bone marrow, spleen; transported by transferrin
Iron Deficiency - Risk
Infants - especially ~6 months due to increased demand and low concentrations in breast milk
Children, adolescents (especially girls due to menstruation and poor intake)
Pregnant Women
Blood loss - bleeding, hemolysis
Obesity - due to chronic inflammation
Post bariatric surgery
Iron Deficiency
Most common micronutrient deficiency - worldwide & US
Anemia (microcytic, hypochromic) - decreased exercise tolerance, fatigue, attention deficit, impaired growth
Iron deficiency without anemia is associated with impaired cognitive functionin the developing brain; irreversible, even with correction
Iron Toxicity
Potent pro-oxidant - avoid unnecessary supplementation
Excess iron deposits as hemosiderin in reticuloendothelial cells; may interfere with absorption of Zn, Cu
Iron Deficiency - Diagnosis
Low Hb/Hct + microcytic/hypochromic anemia
Low ferritin (can be elevevated in infection/inflammation - check ESR/CRP)
Low serum Fe + high TIBC - low % saturation
Zinc - Functions & Sources
Regulation of gene expression (Zn fingers) - important in
Growth and tissue proliferation Immune system Wound healing GI tract integrity Skin
Sources: Animal products (beef > poultry > fish), plants (whole grains, legumes)
Zinc - Homeostasis
Absorption is crudely controlled - inhibited by phytate (like Fe); absorption is NOT increased by Zn deficiency
Excretion from pancreatic-biliary system with loss via the Feces; therefore less toxic than Iron, but increased loss may occur in diarrhea
Zinc Deficiency - Risk
Breastfed infants > 6 months (low supply, high demand)
Pregnant women
Monotonous, plant-based diets
GI illness - diarrhea
Wounds, burns - increased requirement for tissue repair
Zinc Deficiency
Mild: Growth delay/stunting, impaired immune function, poor neurocognitive development
Severe: Dermatitis, diarrhea, immune dysfunction, delayed sexual maturation, delayed wound healing, taste impairment
Acrodermatitis Enteropathica
Mutation in enterocyte Zn transporter ZIP4
Fatal if not treated but responds to high doses of Zn supplements; presents with severe dermatitis of groin and around the mouth, growth failure, diarrhea
Iodine - Sources & Function
Sources: seafood, seaweed, iodized salt
Function: Integral component of thyroid hormones T3 and T4
Zn toxicity
Decreased HDL cholesterol
Decreased Fe and Cu absorption
Diarrhea
Iodine deficiency
Goiter (enlarged thyroid gland) as compensation for decreased T3, T4 production; ‘goitrogens’ are foods that contain ions which compete with iodine uptake, i.e. SCN- in cassava; associated with goiter and hypothyroidism
Iodine deficiency in pregnancy associated with spontaneous abortion and stillbirth, as well as ‘cretin child’ - short stature, developmentally delayed, coarse facies, deaf/mute
Copper deficiency
Intellectual disability, seizures
Connective tissue disease - osteoporosis, fractures
Pathophysiology of marasmus
Normal physiological response to starvation; characterized by decreased insulin and increased counter-regulatory hormones, which mediate eventual shift to lipolysis and ketogenesis; decreased need for glucose in the brain spares muscle protein breakdown
Also associated with decreased energy expenditure (bradycardia, hypothyroidism, hypothermia)
Pathophysiology of Kwashikor
Edematous protein energy malnutrition without wasting; associated with high insulin which inhibits lipolysis and increases fatty acid synthesis in the liver, causing an enlarged, fatty liver
Associated with hypoalbuminemia and edema
Phenotypic findings of Kwashikor
Edema, 'moon faces' Anorexia Psychological impairment Hepatomegaly Diarrhea Skin lesions - 'flaky paint' Hair changes - 'flag sign'
Re-feeding syndrome
Increased insulin secretion in response to feeding drives glucose and K+ phosphorous intracellularly; may cause hypokalemia with associated nerve/muscle dysfunction and hypophosphatemia
Mg2+ requirements increase with metabolic rate as Mg is a co-factor for ATPase
Malnutrition occurs in what percentage of hospitalized patients?
50%
Stunting - Definition & Epidemiology
Height-for-age Z score < -2
More common than wasting; affects 26% of children worldwide; primarily occurs over the critical 1,000 Day window from conception through the first 2 years of life as a result of chronic malnutrition (not energy deficit), inflammation, recurrent infection, intergenerational effects
