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What is the function of zinc?
- Component of various enzymes
- Maintenance of the structural integrity of proteins
- Regulation of gene expression
How is zinc lost?
- Intestinal endogenous losses
- Non-intestinal endogenous losses (skin, sweat, urine, semen)
How is the zinc requirement calculated?
Balance studies- calculate how much is lost, therefor how much needs to be replaced
Why is a mixed protein diet important for zinc absorption?
How does zinc absorption by maternal and embryonic tissues vary during pregnancy?
Increases throughout pregnancy, with the last quarter being 0.73mg/day
What is the fractional absorption of zinc?
How much additional zinc is needed during pregnancy?
- Based on the additional requirement during the 4th quarter (+2.7mg/day)
- +EAR for nonpregnant girls/women (6.8mg/day)
What is the function of iodine?
- Essential component of the thyroid hormones
- Involved in the regulation of various enzymes and metabolic processes
How does Canada and the US combat iodine deficiency?
Do iodine requirements differ with age and/or gender?
How much additional iodine is required during pregnancy?
Estimated daily thyroid iodine uptake by newborn=160ug/day
What can happen due to iodine deficiency during pregnancy?
- Associated with increased incidence of miscarriage, stillbirth, and birth defects
- Severe iodine deficiency during pregnancy may result in congenital hypothyroidism in the offspring
- Fetal iodine deficiency is caused by iodine deficiency in the mother
What is cretinism?
- Most devastating effect of iodine deficiency
- Congenital hypothyroidism
- Severe deficiency
- Irreversible mental retardation
Why is thyroid hormone important during pregnancy?
- Important for myelination of the CNS
- Most active in the perinatal period
- During fetal and early postnatal development
What is the function of selenium?
- A number of Se-dependent enzymes (selenoproteins)- several are oxidant defense enzymes
- Essential for normal development, growth, and metabolism through the regulation of thyroid hormones
How do selenium and iodine react in the body?
- Thyroid gland releases into circulation very small amounts of biologically active TH (thiiodothyronine or T3) and large amounts of an inactive form of TH (thyroxine or T4)
- Most of the biologically active T3 is created by the removal of 1 iodine atom from T4
- Reaction is catalyzed by Se-dependent iodothyronine deiodinase enzymes
What is the EAR for selenium based on?
Based on Se intakes that would maximize glutathione peroxidase activity
What is Keshan disease?
- Cardiomyopathy that occurs almos exclusively in children
- Firmly linked to Se deficiency
- Occurs in areas of China where the population is severely Se deficient
- Occurs in populations that have a plasma glutathione peroxidase activity in men that is 37% of maximum values
Why are Se requirements for both men and women based on the higher reference weights for males?
Reported greater susceptibility of women to develop keshan disease and the fact that the data used to set the EAR came largely from men
How is selenium related to cancer occurrence?
- In some animal models, high selenium intakes decrease the incidence of cancer
- Lower incidence of cancer among individuals on self-selected diets producing high tissue Se
How much is the additional selenium requirement during pregnancy?
- EAR is increased by 4ug/day
- Need accumulation of enough selenium by the fetus to saturate its selenoproteins
- No adjustment for absorption
What is the function of copper?
Component of metalloenzymes acting as oxidases--> reduction of molecular oxygen
What is monoamine oxidase (MAO)?
- Serotonin degradation
- Metabolism of catecholamines (epinephrine, norepinephrine, and dopamine)
What does diamine oxidase do?
What is lysyl oxidase?
- Uses lysine and hydroxylysine as substrates for posttranslational processing
- Produce cross-linkages needed for the development of connective tissues
What are some obligatory losses of copper?
- Urinary losses, GI losses, sweat, hair nails
- Miscellaneous losses (menstrual and semen losses)
What are some functional biochemical measures of Cu status?
- RBC superoxide dismutase activity
- Blood and platelet [Cu]
- Platelet cytochrome c oxidase activity
How much additional Copper is required during pregnancy?
- Total of 18mg Cu
- ~67ug/day of additional Cu is absorbed
- 100ug/day of dietary Cu is needed (65-75% bioavailability)
What is the function of manganese?
- Formation of bone
- Amino acid, lipid, and CHO metabolism
- Arginase, glutamine synthetase, phosphoenolpyruvate (PEP) decarboxylase, manganese superoxide dismutase
- Lycosdyltransferases and xylosyltransferases, important in proteoglycan synthesis --> bone formation
How is the additional requirement for manganese during pregnancy determined?
Determined by extrapolating up according to the additional weight gained of 16kg
What is the function of chromium?
- Potentiates the action of insulin to maintain glucose tolerance
- Possibly by activating insulin receptor activity
- A low-molecular-weight chromium-binding substance (LMWCr) may enhance the response of the insulin receptor to insulin
Why is chromium important during pregnancy?
- Cr is depleted throughout pregnancy and with multiple pregnancies
- Cr higher in tissues at birth and declines rapidly with age
- Need for deposition in the fetus from the mother
- Low [Cr] in human milk--> infant may use stored Cr during early months of life
How is the AI for chromium during pregnancy determined?
By extrapolating up from adolescent girls and adult women
What is the function of molybdenum?
Cofactor in Mo-containing enzymes (mlybdoenzymes)
How is the molybdenum requirement determined?
- Average minimum Mo requirement for maintaining adequate status is estimated to be 22ug/day plus an increment for miscellaneous losses (estimated to be an additional 3ug/day)
- Total requirement is 25ug/day
- With an average bioavailability of 75%, the EAR is 34ug/day
How is the additional requirement of Mo during pregnancy determined?
Extrapolated up from adolescent and adult women using median weight gain of 16kg
What is the function of fluoride?
- Crystalline deposits in bone and teeth
- Forming the more decay-resistant fluorapatite in developing teeth
- Helps prevent dental caries
- In erupted teeth it promotes remineralization of early lesions in the enamel and suppresses bacterial metabolism and reduces the amount of acid they produce
What is the AI for fluoride based on?
- Based on extensively documented relationships betwee caries experience and water [F]+F intake
What are the sources of fluoride?
Primary source: fluoridated drinking water