4. MICRONUTRIENT MINERALS
Try these Questions:
Use "Quick Answer" Buttons to see if you're correct
Q1. Pick best answer. Which of these nutrients has not been put in water or foods (fortification) to prevent childhood disease?
A Fluoride
B. Iodide
C. Iron
D. Zinc
Q2. Pick best answer. Mild Iron deficiency in infancy and early childhood (HGB 10 to 11 mg/dL) is associated with:
A. developmental delay and clinical symptoms
B. developmental delay but no clinical symptoms
C. clinical symptoms but no developmental delay
D. No clinical symptoms or developmental delay
Q3. Pick best answer: Contemporary diets are associated with negative calcium balance because they:
A. are high in sodium and low in potassium
B. have high protein and phosphorous content
C. are high in fat content
D. All of the above
And these techniques:
1. Send class to a supermarket, a bodega, and a mega store with an imaginary $17 in their pockets, the cost in 2007 of the Thrifty Food Plan (TFP) of the USDA for a family of 4 for one day. Let them list the foods and calculate whether they reach the RDA for the minerals in the Nutrition Notes obtaining 10,000 calories. Give ½ the group a menu from the Thrifty Food Plan and let ½ go to the stores unguided. They will have to approximate food costs in that some bulk purchases will be needed. Prorating is fine, but the weekly cost for that item should be calculated since the limit for 1 week will be $17 x 7 = $119.
4a. Micronutrient Minerals--Iron
Iron is a mineral that is ubiquitous in nature and essential for humans both as catalyst for reactions [cytochrome and monoamine oxidases, gamma amino butyric acid (GABA)] and molecular structure (hemoglobin). Though humans have mechanisms for absorption, distribution and preservation of iron, in industrial societies, iron deficiency is the most common micronutrient deficiency in childhood with developmental delay as its most important consequence.
Important terms and concepts
Hemoglobin (HGB) concentration; mean corpuscular volume (MCV); anemia; reticulocytosis; erythrocyte protoporphyrin (EP); percent saturation; ferritin level.
Requirements
The ratio of RDA for iron to RDA for energy parallels the prevalence of iron deficiency at any age. Typical US diet has about 0.6mg iron/100 calories. When the ratio for RDA is greater than the concentration of iron to energy in the diet, the child is at-risk for iron deficiency.
TABLE
Iron needs at different ages with ratio of required iron adjusted for energy.
* increased need because of menses
** "at-risk" for iron deficiency
*** RDA for energy is based on a balance between intake and
expenditure, not an absolute for intake.
CAPTION: Iron needs each day drop after infancy and for boys and men remain at 10 mg of elemental iron each day. By contrast, energy levels rise with age so that the ratio of iron to energy needed in the diet is lower and iron deficiency should be an uncommon phenomenon past infancy. Iron deficiency at school age suggests poverty and a disrupted social environment. [see Karp, 1974]
Of note, iron deficiency with anemia has been decreasing in the United States for the past 20 years. This, we believe, is a result of successful programs to fortify infant formulae and cereal with iron and to direct provision of these foods to poorer children. Figures 2a and 2b show that as use of cow milk has declined and iron-fortified formula has increased (2a), the prevalence of anemia has fallen.
Figures 2a and 2b. Relative proportion of infant feeding methods at 5-6 m. of age in US; o = anemia prevalence [HGB <10.3g/dl (infants); <10.6g/dl (older)]
The consequences of iron deficiency
This description, from 1913, applies to children with a HGB <7.0 g/dl.
"[They] usually exhibit many symptoms of [protein-energy] malnutrition. Their tissues are flabby; they are generally below average in height ....There is easy fatigue, shortness of breath on exertion.... peripheral circulation is poor....anaemic murmurs are heard over the base of the heart....pallor of the skin and mucous membranes is present in most cases, but it is not an accurate guide as to the degree of anaemia. This can only be determined by an examination of the blood...."
Children with mild anemia may have no apparent symptoms. Most importantly, iron deficiency is associated with diminished activity of iron-catalyzed enzymes in the CNS including mono- amine and cytochrome oxidases affecting learning even without anemia. Moreover, children learn by exploration so that the lethargy of iron deficiency anemia affects development.
Diagnosis
There are three levels of iron nutrition as shown: 1) normal balance, 2) depletion or deficiency without anemia, and 3) deficiency with anemia. [normal = nl; infant = I; older child = O]
TABLE
An MCV<70u3 and RDW>14.6 suggest iron deficiency, and an EP>70ug/dl has been considered suggestive of iron deficiency and or lead poisoning. In either circumstance, further evaluation is warranted.
Screening high-risk children for HGB, MCV and RDW should be performed in the second six months of life and yearly thereafter to school age.
Prevention
Prevention, rather than treatment, is essential as the learning failure may not be reversible. All infants require a source of iron from formulae or supplement. Older children require a nutritious diet (2 cups of milk a day, limited non-nutritious ("junk") food, affordable iron containing foods). Children from poor families dependent on convenience foods are at high-risk because non-nutritious items ("chips") may be consumed. The importance of supplemental food plans (WIC, Food Stamps, and School Feeding) cannot be over emphasized.
The combination of rice, beans and meat consumed with fresh citrus fruit provides an excellent source of absorbable iron, but spinach, dried fruits, and vegetables consumed without meat are poor sources. Iron supplements are suggested for poor children through the first two years of life.
Treatment
All anemic children require a careful assessment of the diet and parental counseling. Because ferrous sulfate is readily absorbed in iron deficiency, a low dose (2-3mg/kg/day) for three months followed by multivitamins with iron and dietary supplementation will provide for rapid recovery. A child with iron deficiency anemia will show reticulocytosis within one week of the initiation of therapy.
Good nutrition is an essential element in therapy for iron deficiency.
4b. Micronutrient Minerals--Calcium
Calcium (Ca) need far exceeds that of any other mineral. While the strength of bone is influenced by the admixture of other minerals (e.g., fluoride), calcium is the principal mineral of the bony matrix. Moreover, Ca from bone provides the reservoir to maintain constant levels in blood for the sake of autonomic, voluntary (skeletal) and cardiac muscle function and the clotting cascade. While Ca deficiency is unusual for the full term baby fed either human milk or manufactured formula, low birth weight infants, especially those fed "home made", high phosphate, low calcium cow milk formulas may become hypocalcemic. The same is true for children with malabsorption and hereditable disorders of parathyroid and/or Vitamin D metabolism.
Hypercalcemia, though uncommon, may be seen in childhood with hyperparathyroidism, excess intake of vitamin D, sarcoidosis and tumors secreting Vitamin D-like hormones. Calcium absorption from the gut is enhanced by Vitamin D. Calcitonin promotes deposition of Ca into bone for structure and storage. [see section 5c (Vitamin D) for further comments on calcium metabolism.]
Terms
Rickets and osteomalacia, osteoporosis, elemental calcium, calcium balance.
Requirements
Older men and postmenopausal women have seemingly obligate negative calcium balances. Thus, positive balance, with depositions of 100 mg/day of elemental Ca in children and 250 mg/day in adolescence and early adult life, are essential to prevent osteoporosis later in life. High protein, high phosphate diets increase the need in daily Ca intake.
Consequences
Rickets, a failure of ossification of osteoid with a resultant softening and deformation of growing bone, is a disease of children and a consequence of Vitamin D, phosphate or calcium deficiency. This deficiency in adults is referred to as osteomalacia (see section 5c ). While Vitamin D deficiency and concomitant failure to provide bone with calcium can affect the mineralization of the bony matrix, for the most part, the failure to maintain adequate bone density is a separate entity, osteoporosis. While osteoporosis is a disease found most commonly in postmenopausal women and elderly men, its nutritional origins are in childhood and adolescent life. Thus the high requirements set by RDA shown below.
RDA and nutrient densities required to maintain healthy calcium balance:
** Older girls require 1200mg of Ca for a 2000cal diet, while older boys require 800mg for a 3,000 calorie diet.
Prevention
The absorption of Ca from the gut and excretion into the urine are greatly influenced by other constituents in the diet. It is well known that people living in developing countries without access to dairy products maintain excellent bone density with modest intakes of Ca. Contemporary diets have high animal protein and phosphorous content with low Ca/P ratios. These characteristics are potentially harmful in that they "promote hypercalciuria and stimulate release of parathyroid hormone with resultant progressive decrease in bone mass." Simply stated, a diet promoting healthy bone formation will have adequate calcium, a high Ca/P ratio, without excess protein.
TABLE: Levels of Ca, Ca/P, and protein content for breast milk, formula, and cow milk.
Guidance:
1. Consume foods high in calcium content. These include: almonds, swiss cheese, collards, sardines and salmon with bones, spinach, ice cream, kale, beet greens, cheddar cheese, molasses, oysters, milk, stalk broccoli, and Farina with milk. Dairy foods are highest in calcium content. Past two years of age, two or three servings of low fat dairy products are recommended.
2. Maintain a healthy "life style." This includes: not smoking, regular exercise against gravity, reasonable exposure to sunlight and/or adequate Vitamin D intake. Highly fit women, however, increase their risk for osteoporosis as leanness decreases the fat mediated production of estradiol and excess exercise induces amenorrhea.
3. Heritable factors cannot be changed, but a large bone structure and possibly African ancestry are helpful in prevention of osteoporosis.
4c. Micronutrient Minerals -- Zinc, Magnesium, Iodine and Fluoride
ZINC
Zinc is essential for growth. A syndrome of growth retardation, sexual immaturity and mental retardation associated with zinc and iron deficiency has been found among Egyptian and Iranian children consuming high levels of these nutrients. Their diet was so fibrous that these minerals could not be absorbed. Zinc deficiency associated with growth retardation, and some developmental delay has been found in disadvantaged populations in the United States. Nutritional status and learning ability improved with zinc supplementation in the context of a broad range of support provided by an active "Head Start" program.
Requirements
The RDA for zinc ranges from 3mg for infants to 15mg for adults to 25mg for pregnant and lactating women.
TABLE: The zinc content of foods
** As noted above, excessively fibrous diets may inhibit zinc absorption. "Net delivery of zinc, or any nutrient, to the organism," writes Noel Solomons, "is a function of the total amount of zinc and the bioavailability (fractional absorption). On a meal for meal basis, it is unlikely that the increased zinc in whole grains provides more of the nutrient than highly refined grains, but diets using totally unrefined foods will affect mineral nutritional status."
Measurement of nutrient
Serum red or white cell zinc can be measured and compared to standards. These are notoriously unreliable indicators of zinc status. Functional measures of deficiency including leukocyte chemotaxis, taste and smell acuity and zinc retention after a test dose may be more meaningful.
IODINE and FLUORIDE
Other minerals often missing from the diet in some communities but not in others include iodine (I) to prevent goiter and fluoride (Fl) to strengthen teeth and bones. Iodine has been supplemented to populations by adding the mineral to table salt (NaCl) and fluoride by addition to water supplies. Both strategies are examples of effective public health strategy to prevent disease without adversely affecting any individual.
The graph shown below shows how providing a water supply with one part per million (ppm) of Fl decreases the standard dental count of "Decayed, Filled, or Missing" (DFM) teeth without increasing the occurrence of fluorosis.
MAGNESIUM
The requirement for magnesium (Mg) in the diet, given the rarity of primary deficiency in a free living population, is set from an analyses of consumption data and older balance studies. For infants, the content of Mg in human milk sets the standard. Infants consume 40 to 70 mg per day rising to 250 mg/day in older children. It is recommended that adults take in 300 to 400 mg/day or approximately 15mg/100cal of energy intake. The RDA for Mg during pregnancy is 450mg/day.
The need for Mg is ubiquitous as Mg serves as a catalyst in "at least 300 enzymatic reactions." In children, deficiency of Mg is often expressed as muscle twitching with tetany. Decreased serum Mg is associated with decreased excretion of parathyroid hormone [PTH] with resultant decrease in serum calcium levels and tetany.
** [Mg] --> PTH --> [Ca] **
Magnesium deficiency is found in malabsorption, renal tubular dysfunction, several endocrinopathies including Bartter's Syndrome and maternal hyperparathyroidism. While dietary deficiencies are unlikely in healthy children and adults, alcoholics, children with protein-energy malnutrition, burn patients, and women with unsupplemented lactation do become Mg deficient.
The answers
1. The answer is D. Fluoride in water has been effective in limiting tooth decay. Iodination of salt has been widely and wildly successful in prevention of cretinism; iron in formulae has limited iron deficiency in older infants and toddlers. It is also put in infant cereal. Zinc is a difficult mineral to work with and has not been used successfully I fortification.
2. The answer is B. Mild anemia is unassociated with clinical signs or symptoms, but there are substantial delays. As shown by Lozoff and colleagues, these deficits last a lifetime. (see module on iron deficiency).
3. The answer is B. Contemporary diets have high animal protein and phosphorous content with low Ca/P ratios. These characteristics are potentially harmful in that they "promote hypercalciuria and stimulate release of parathyroid hormone with resultant progressive decrease in bone mass." Simply stated, a diet promoting healthy bone formation will have adequate calcium, a high Ca/P ratio, without excess protein.
Teaching technique:
Mass survey techniques are quite informative. Smaller versions of this technique could be used to address the difficulty in obtaining sufficient expensive micronutrients such as zinc and iron.
