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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
How many people consume the recommended amount of calcium?
Only ~13% of males and 4% of females consume 100% of the recommendation (1200mg/day)
What are some risks of calcium deficiency?
- Increased risk of osteoporosis
- Colon cancer
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
Why is there an increase in calcium absorption during pregnancy?
Increase in blood [1,25(OH)D] during pregnancy
How much additional calcium is required during pregnancy?
No evidence supports increased need for dietary calcium during pregnancy
Where is most phosphorous found in the body?
85% of the adult body phosphorous is in bone
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
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
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]
What is the function of magnesium?
required cofactor for 300 enzymes
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
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
What is the additional requirement for magnesium during pregnancy?
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
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
What are some basal losses of iron?
Obligatory losses in feces, urine, and sweat and from the exfoliation of skin cells
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])
What type of iron is more bioavailable?
Why is nonheme iron not as good?
Strongly influenced by its solubility and interaction with other meal components in upper intestinal lumen
What bioavailability is used to estimate iron requirements on a typical mixed diet?
Which group of individuals has the highest iron requirement?
Women ages 19-50 (due to menstrual losses)
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
How does iron deficiency during pregnancy affect the fetus?
Maternal anemia is associated with premature delivery, low birth weight, and increased perinatal infant mortality
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
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
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