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What is the calcium RDA dependent on?
- Relies on Ca balance studies
- Intakes at which small gains in bone mineral content can be achieved
- Based on clinical trial data showing an increase in bone mineral density in women provided with intakes of 1000mg/day
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How many people consume the recommended amount of calcium?
Only ~13% of males and 4% of females consume 100% of the recommendation (1200mg/day)
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What are some risks of calcium deficiency?
- Increased risk of osteoporosis
- Hypertension
- Colon cancer
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How much calcium is transferred to the fetus during pregnancy?
- ~25-30g of Ca transferred to the fetus
- The majority of this transfer occurs during the 3rd trimester
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Why is there an increase in calcium absorption during pregnancy?
Increase in blood [1,25(OH)D] during pregnancy
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How much additional calcium is required during pregnancy?
No evidence supports increased need for dietary calcium during pregnancy
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Where is most phosphorous found in the body?
85% of the adult body phosphorous is in bone
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Why is phosphorous important?
- Buffers acid or alkali excess to maintain normal pH
- Temporary storage and transfer of the energy derived from metabolic fuels
- Required for phosphorylation, the activation of many catalytic proteins
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How much additional phosphorus is required during pregnancy?
- No evidence to support a increase in EAR for phosphorus
- Intestinal absorption is increased by 10% during pregnancy, which is sufficient for fetal needs
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Where is magnesium found in the body?
- 50-60% in bone
- 1/3 of skeletal Mg is exchangeable as a reservoir for maintaining a normal extracellular [Mg]
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What is the function of magnesium?
required cofactor for 300 enzymes
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Why do elderly people require more magnesium?
- With age, there is an increase in high fiber diets
- Renal function is critical to maintenance of Mg status; and declines with age
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Why is there a need for more magnesium during pregnancy?
- Decrease in serum [Mg], thought to be due to hemodilution
- No data indicating that Mg is conserved during pregnancy or intestinal absorption is increased
- Weight gain alone may result in a greater requirement for Mg
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What is the additional requirement for magnesium during pregnancy?
35mg/day
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What is the function of iron?
- Component of a number of proteins, including enzymes and hemoglobin
- Almost 2/3 of Fe is found in hemoglobin present in circulating erythrocytes
- 15% of myoglobin in muscle tissue
- Variety of enzymes necessary for oxidative metabolism and many other critical functions
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What are the factors used to determine Fe requirement?
- Basal iron losses
- Menstrual losses
- Fetal requirements during pregnancy
- Growth: expansion of blood volume and/or increased tissue and iron storage
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What are some basal losses of iron?
Obligatory losses in feces, urine, and sweat and from the exfoliation of skin cells
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How is dietary absorption determined?
- The proportion of dietary iron absorbed is determined by the iron requirement of the individual
- Body Fe store regulates absorption (% absorbed is inversely proportional to serum [ferritin])
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What type of iron is more bioavailable?
Heme iron
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Why is nonheme iron not as good?
Strongly influenced by its solubility and interaction with other meal components in upper intestinal lumen
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What bioavailability is used to estimate iron requirements on a typical mixed diet?
18%
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Which group of individuals has the highest iron requirement?
Women ages 19-50 (due to menstrual losses)
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What are the consequences of iron deficient anemia during pregnancy for the mother?
- Severe anemia can lead to perinatal maternal mortality
- Moderate anemia is associated with a two-fold risk of maternal death
- Causes of death such as heart failure, hemorrhage, infection
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How does iron deficiency during pregnancy affect the fetus?
Maternal anemia is associated with premature delivery, low birth weight, and increased perinatal infant mortality
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Why is iron so important during pregnancy?
- Fe deficiency limits the expansion of maternal erythrocyte cell mass
- Decreases hemoglobin synthesis, increases workload of maternal hear to supply fetus with O2 which can lead to abnormal fetal development
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Why must pregnant women take iron supplements?
- Habitual canadian diet cannot meet such high Fe RDA
- Supplementation uses the assumption of inadequate pre-pregnant Fe stores
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What is used to determine the pregnancy RDA for iron?
Set by estimating the requirement for absorbed Fe at the 97,5 percentile and using an upper limit of 25% iron absorption and rounding
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