Trace Minerals

Trace Minerals Overview

• “A daily nutritional need of less than 100 mg”
• Understanding of trace mineral metabolism is growing
• Actual need for trace minerals is debatable
• Difficulties studying trace minerals
  • Only minute amounts needed by body
  • Sophisticated technology required for research
  • Induce deficiency is difficult in studies
  • Clinical signs and symptoms may only appear with severe deficiency
  • Certain tests not reliable
• Nutrient Needs For Trace Minerals
  • Many have RDA, most have only an Adequate Intake (AI)
  • Mineral nutrient needs based on “balance studies”
  • Balance study indicates the amount of dietary intake needed to maintain a specific pool
  • Minerals interact with each other which cause complications of trying to individually set dietary needs
• Trace minerals in food
  • Minerals in plants directly related to mineral content of soil
  • Minerals in animals higher because of the variety of plants and other foods consumed

Trace Minerals

Iron (Fe)

• Found in every cell and about 5 grams in the entire body
• Large difference between men (50mg/kg) and women (40mg/kg)
• 70% of iron in the body is found in hemoglobin
• Factors that influence iron absorption:
  • Increased absorption:
    • Gastric acid
    • Heme iron in food
      • Myoglobin and hemoglobin
    • Iron transport
      • Transferin
    • Iron stores
      • Ferritin
      • Hemosiderin
    • Vitamin C
      • Form chelates (complex compound with a central metallic ion)
        
  • Decreased absorption:
    • Phytic acid (in dietary fiber)
    • Oxalic acid (in leafy vegetables)
    • Polyphenols in tea
    • Full body stores
    • Excess of other minerals (Zn, Mn, Ca)
    • Reduced gastric acid output
    • Some antacids
• Functions:
  • Transport of oxygen in hemoglobin
  • Involved in electron transport chain in cell respiration
  • Iron in peroxidase enzymes helps break down hydrogen peroxide
  • Others: immune function, cognitive development, temperature regulation
• Deficiency
  • Reduction  in red blood cell production – iron deficiency anemia
  • Produces fatigue
  • Hematocrit levels below 34-37% and blood hemoglobin < 10-11 g/100 ml blood
  • Other causes of iron deficiency anemia: hemorrhaging, ulcers, hemorrhoids, and colon cancer
  • Measuring iron status (stores): ferritin (< 12 ng/ml) in the blood
  • Progression of iron deficiency: increased free or non-heme erythrocyte protoporphyrins (FEP) and microcytic hypochromic anemia
  • Treatment of iron deficiency anemia is iron sulfate
• Sources: steamed oysters, cooked spinach, cooked kidney beans, sirloin steak, pot roast, fried beef liver, prune juice
• RDA: 8 mg for men and 18 mg for women
• Toxicty:
  • >45mg/day
  • GI upset
  • In patients with hematochromatosis which causes increased iron absorption

Zinc (Zn)

• Foods with phytic acids causes decreased zinc bioavailability
• Zinc is absorbed throughout the small intestine
• Factors affecting absorption include body’s need for zinc and the composition of the meal in which zinc is consumed
• Zinc is released into the blood stream and bound to proteins (albumin) for transport to liver which releases zinc into general circulation
• Zinc induces production of metallothionein which aids in the homeostatic regulation of zinc absorption
• Functions:
  • Zinc is a cofactor of nearly 100 enzymes
  • Nucleic acid synthesis and function
  • Protein metabolism, wound healing, growth
  • Immune function
  • Development of sexual organs and mineralization of bone-matrix
  • Storage, release, and function of insulin
  • Cell membrane structure and function
  • Component of superoxide dismutase (prevents oxidative damage to cells)
  • Carbonic anhydrase which forms carbonic acid (maintains acid-base balance in blood)
  • Alcohol dehydrogenase (alcohol metabolism)
• Deficiency: skin rash, diarrhea, decreased appetite and sense of taste, hair loss, poor growth and development, poor wound healing
• Sources: steamed oysters, sirloin steak, pot roast, lamb chop, canned crab meat, wheat germ, fried beef liver, roasted turkey, cooked black-eyed peas
• RDA: 11 mg/day men and 8 mg/day women
• Toxicity: > 40mg/day, can reduce copper absorption, diarrhea, cramps, depressed immune function

Copper (Cu)

• Copper is primarily absorbed in the stomach and duodenum of small intestine
• 12-75% of dietary copper is absorbed
• Phytates, dietary fiber, and high dose supplements of vitamin C, zinc, and iron may interfere with absorption
• Ceruplasmin, albumin, and transcuperin transport copper to liver and kidney then body tissue
• Most copper in body is found in liver, brain, blood, skeletal muscle, and bone
• Functions:
  • Aids in iron absorption
  • Part of enzyme
    • involved in collagen and elastin synthesis
    • in electron transport chain
    • that converts dopamine to norepineprine
    • involved in myelin (insulates nerves)
  • involved in antioxidant reactions
• Deficiency: anemia, low white blood cell count, poor growth
• Sources: steamed oysters, steamed lobster, fried beef livers, brazil nuts, brewer’s yeast, walnuts, sunflower seeds, cooked kidney beans
• RDA: 0.9 mg/day (900 ug/day)
• Toxicity: >8-10 mg/day, vomiting, nervous system disorders,

Selenium (Se)

• Found in many ionic forms but most selenium is bound to the amino acids methionine and cysteine
• Bioavailability higher than iron and zinc
• 50-100% of dietary selenium is absorbed
• Functions: cofactor for the enzyme glutathione peroxidase which is used in antioxidant reactions
• Deficiencies: muscle pain, muscle weakness, Keshan disease (form of cardiomyopathy)
• Sources: canned tuna, sirloin steak, shrimp, cooked egg noodles, roasted ham, roasted chicken, boiled egg, whole-wheat bread, oatmeal
• RDA: 55 ug/day
• Toxicity: >400 ug/day, nausea, vomiting, hair loss, weakness, liver disease (cirrhosis)

Iodide (I)

• Deficiency linked to goiter in 1920s
• Commonly found in fortified table salt
• Absorbed along GI tract and transported as free ions in blood
• 75% of iodide found in the thyroid and is used in the synthesis of thyroid hormone (T3 ad T4)
• Functions: used in the synthesis of thyroxine (T4) which is converted to T3, T3 used in controlling the rate of cell metabolism
• Deficiency: goiter, mental retardation, cretinism
• Sources: iodized salt, baked haddock, buttermilk, baked cod, cottage cheese, mozzarella cheese, shrimp, boiled egg
• RDA: 150 ug/day
• Toxicity: >1.1 mg/day, inhibition of thyroid hormone synthesis and toxic goiter development

Fluoride (F)

• 80-90% of dietary fluoride absorbed throughout GI tract
• transported in free ionic form in blood
• 50% of iodide absorbed is deposited in calcified tissues, bones, and teeth
• Functions: reduces dental caries by
  • Reducing acid solubility of the enamel
  • Promoting remineralization of enamel lesions
  • Increase the deposition of minerals that retard the development of cavities
  • Reducing the net rate of transport of minerals from the enamel surface
• Deficiency: increased risk of dental caries
• Sources: drinking water, tea, seafood, and seaweed
• Adequate Intake: 3.8 mg/day for men and 3.1 mg/day for women
• Toxicity: >10 mg/day, fluorosis, upset stomach, mottling of teeth, bone pain

Chromium (Cr)

• 2-10% of dietary chromium is absorbed
• bioavailability hard to asses
• Functions: enhances insulin action
• Deficiency: high blood glucose
• Sources: egg yolks, whole grains, pork, nuts, mushrooms, beer
• Adequate Intake: 35 ug/day for men and 25 ug/day for women
• Toxicity: only when exposed in industrial settings

Manganese (Mn)

• Functions: Cofactor in enzymes
  • Pyruvate carboxylase – involved in carbohydrate metabolism
  • Superoxide dismutase – involved in antioxidant reactions
• Deficiency: none observed
• Sources: nuts, oats, whole grains, beans, tea, leafy vegetables
• Adequate Intake: 2.3 mg/day for men and 1.8 mg/day for women
• Toxicity: >11 mg/day, psychiatric abnormalities, hyperirritability, violence, hallucinations, and impaired control of muscles

Molybdenum (Mo)

• High amounts of molybdenum may inhibit copper absorption
• Component of enzyme xanthine dehydrogenase which is involved in the formation of uric acid and mobilization of iron from liver ferritin stores
• Deficiency: none observed
• Sources: milk, liver, beans, grains, nuts
• RDA: 45 ug/day
• Toxicity: none observed