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Why is adequate potassium intake important?
- Lowering blood pressure
- Blunting the adverse blood-pressure effects of salt intake
- Reducing the risk of kidney stones
- Potentially reducing bone loss
What is the AI for potassium?
Does the potassium requirement change during pregnancy?
Where is most potassium found in the body?
Most potassium is intracellular
Does sweating increase potassium requirement?
Sweat potassium is a small percentage of available potassium, BUT sweating does increase the dietary requirement (athletes)
How much sodium does the average diet provide?
Why is there a large variation in sodium needs?
Because the more a person sweats, the more a person excretes
In sedentary individuals, how is Na lost?
- Primary route of loss is urine
- Kidneys can conserve or excrete Na as needed
Does the Na requirement change during pregnancy?
Why is more sodium needed during pregnancy?
- Maintain the increase in plasma volume
- Provide for the products of conception
- This accumulation occurs over 9 months
Where is sulfur found in the diet?
Present in the amino acids (methionine, cysteine and cystine) in proteins
What is sulfur used for in the body
A component of essential compounds such as glutathione (a potent antioxidant)
What is glutathione?
A potent antioxidant involved in the detoxification reactions of drug and toxins
Why is there no RDA for sulfur?
North American diet is adequate-to-excessive protein intake, so there is no need to set RDA
What is the function of thiamin?
Functions as a coenzyme in the metabolism of CHO and branched-chain amino acids
What is the thiamin requirement based on?
- Thiamin needed to achieve and maintain RBC transketolase activity
- Without excessive thiamin excretion
How is thiamin status assessed?
- Erythrocyte transketolase activity
- [thiamin] and its phosphorylated esters in blood
- Urinary thiamin excretion under basal conditions or after thiamin loading
What is the biological function of thiamin?
Function as thiamin pyrophosphate (TPP) in the metabolism of CHO
Is thiamin requirement increased during pregnancy?
Increased by ~30%
Why is thiamin requirement increased during pregnancy?
- Increased growth in maternal and fetal compartments (20%)
- Small increase in energy utilization (10%)
What is the RDA for thiamin during pregnancy?
What is the function of riboflavin?
Coenzyme in numerous oxidation-reduction reactions
What is the riboflavin requirement based on?
- Erythrocyte glutathione reductase activity coefficient
- RBC [riboflavin]
- Urinary riboflavin excretion
Is there a need for increased riboflavin during pregnancy?
Yes, additional riboflavin requirement of 0.3mg/day
What is the increase in riboflavin requirement during pregnancy based on?
- Increased growth in maternal and fetal compartments
- A small increase in energy utilization
What are the functions of niacin?
Cosubstrate or coenzyme for the transfer of the hydride ion with numerous dehydrogenases
Why is the niacin requirement expressed as niacin equivalents?
- Different niacin sources have different bioavilability
- Allows for some conversion of the a.a. tryptophan to niacin
Is niacin requirement increased during pregnancy?
no direct evidence to suggest a change in the niacin requirement during pregnancy
What is the function of B6?
Vitamin B6 (pyridoxine and related compounds) functions as a coenzyme in the metabolism of amino acids, glycogen, and sphingoid bases
What is the primary criterion for setting the B6 RDA?
Maintenance of adequate blood 5'-pyridoxal phosphate levels
Is B6 requirement increased during pregnancy?
Yes, there is significant fetal uptake of vitamin B6
How much is B6 requirement increased during pregnancy?
- ~2mg/day of supplemental B6 in the 1st trimester
- 4-10mg/day in the 3rd trimester
- Additional average pregnancy need is 0.25mg
How much B6 is accumulated throughout the pregnancy?
Fetus and placent accumulate ~25mg of B6
What is the function of folate?
Coenzyme in single-carbon transfers in the metabolism of nucleic and amino acids
What is the primary indicator for RDA estimates of folate?
- Erythrocyte folate
- Blood [homocysteine] and [folate]
Why are dietary folate equivalents used for the RDA of folate?
To adjust for the nearly 50% lower bioavailability of food folate compared with that of folic acid
Do folate requirements increase during pregnancy?
Yes, requirements increase substantially
Why is there an increase in folate requirement during pregnancy?
- Marked acceleration in single-carbon transfer reactions
- Including those for nucleotide synthesis and thus cell division
- Uterine enlargement
- Placental development
- Expansion of maternal erythrocyte number
- Fetal growth
What happens as a result of inadequate folate intake?
- Maternal serum and erythrocyte [folate] is decreased
- Megaloblastic marrow changes may occur
- Megaloblastic anemia may develop if inadequate intake continues
What is the primary indicator of folate inadequacy?
Erythrocyte folate maintenance (reflects tissue stores)
What is the EAR for folate in pregnant women?
- EAR for nonpregnant women+supplementation=EAR for pregnant women
Why is folate required for women capable of becoming pregnant?
Decrease risk of NTD for women capable of becoming pregnant
What are the functions of B12?
- Coenzyme for a critical methyl transfer reaction that converts homocysteine to methionine
- A separate reaction that converts L-methylmalonyl-coenzyme A (CoA) to succynyl-CoA
What is the RDA for B12 based on?
Based on the amount needed for the maintenance of hematological status and normal blood vitamin B12 values
Why is B12 absorption increased during pregnancy?
Due to an increased number of intrinsic factor-B12 eceptors
What happens to serum total [B12] during pregnancy?
- Serum total [B12] begins to decrease in the 1st trimester (more than could be accounted for by hemodilution)
- Further decrease through the 6th month to about half of non-pregnancy concentrations (some of the later decrease is due to hemodilution)
Is maternal stored B12 transfered to the fetus?
- No, only newly absorbed B12 is readily transported across the placenta
- Maternal liver stores are less important source of the vitamin for the fetus
When does fetal B12 deficiency often occur?
When the mother has been a strict vegetarian for only 3 years
How much is EAR for B12 increased during pregnancy?
EAR is increased by 0.2ug/day to give 2.6ug/day
What are the functions of Biotin?
Functions as a coenzyme in bicarbonate-dependent carboxylation reactions
What are some factors affecting biotin requirements?
- Ingestion of large amounts of raw eggwhite (avidin binds biotin)
- Biotinidase deficiency (genetic)
- Anticonvulsants (induce biotin catabolism)
What is the function of choline?
Precursor for acetylcholine, phospholipids, and the methyl donor betaine
What is the primary criterion for estimating the AI
Prevention of liver damage as assessed by serum alanine aminotransferase levels
What are the 2 forms of choline available in the diet?
- Free choline
- Bound as esters such as phosphocholine, glycerophosphocholine, sphingomyelin, or phosphatidylcholine
What is phosphatidylcholine used for?
- Used as a treatment to lower blood cholesterol
- lecithin-cholesterol acyltransferase plays an important role in the removal of cholesterol from tissues
What is the endogenous pathway for the denovo biosynthesis of choline?
Sequential methylation of phosphatidylethanolamine using S-adenosylmethionine as the methyl donor
How is the demand for dietary choline modified?
Modified by the metabolic methyl-exchange relationships between choline and three nutrients: methionine, folate, and vitamin B12
What happens during choline dificiency?
- Decreased plasma [choline] and [phosphatidylcholine]
- Develop liver damage
What is the choline requirement influenced by?
- The availability of methionine and folate in the diet
- Gender, pregnancy, lactation and stage of development
Why is the AI for choline so uncertain?
Based on only one study
When is choline most important in pregnancy?
During embryogenesis and perinatal development
What is the function of pantothenic acid?
Component of coenzyme A and phophopantetheine (fatty acid metabolism)
What is used to estimate the AI of pantothenic acid?
Intake adequate to replace urinary excretion of pantothenic acid
What is the AI for pantothenic acid?
5mg/day- set using only one study of the relationship between daily intake and excretion in adults
What is the AI for pantothenic acid for pregnancy?
- No information showing that usual intakes in US and Canada are inadequate to support a healthy pregnancy outcome
- Rounding up from the average intake in AI of 6mg/day for pregnant women
What are the functions of vitamin C?
- Water-soluble antioxidant
- Cofactor for enzymes involved in the biosynthesis o collagen, carnitine and neurotransmitters
What is the RDA for vitamin C based on?
- Maintain near-maximal neutrophil concentration
- With minimal urinary excretion of ascorbate
What is the RDA of vitamin C?
- 90mg/day for men
- 75mg/day for women
Why is additional vitamin C needed for pregnancy?
Maternal plasma [vitamin C] decrease with the progression of pregnancy due to hemodilution and active transfer to the fetus
How much vitamin C is needed to prevent young infants from scurvy?
Which subpopulations of pregnant women require even more vitamin C?
- Users of street drugs and cigarettes
- Heavy users of alcohol
- Regular users of aspirin
What is the function of vitamin A?
- Normal vision
- Gene expression
- Embryonic development
- Immune function
What is EAR for vitamin A based on?
The assurance of adequate stores
Where does vitamin A come from in the diet?
- Preformed vitamin A abundant in some animal-derived foods
- Provitamin A carotenoids abundant in darkly coloured fruits and vegetables, oily fruits and red palm oil
What are the retinol activity equivalents for beta-carotene, alpha-carotene and beta-cryptoxanthin?
12, 24, and 24 respectively
Why is body pool size important for vitamin A EAR?
The body pool size will assure vitamin A reserves to cover increased needs during periods of stress and low vitamin A intake
What is the vitamin A EAR for pregnancy based on?
- Accumulation in the liver of the fetus during gestation
- Assumption that liver contains ~1/2 the body's vitamin A when liver stores are low, as in the case of newborns
What is the efficiency of maternal vitamin A absorption?
How much is the vitamin A requirement increased for pregnant women?
Increased by 50ug/day during the last trimester
What is the function of vitamin D?
- Enhances absorption efficiency of small intestine (Ca, P)
- Maintains blood [Ca], [P]
- Potent antiproliferative and prodifferentiation effects in a variety of tissues
What are the major physiologically relevant forms of vitamin D?
- Vitamin D2 (ergocalciferol) from yeast and plant serols)
- Vitamin D3 (cholecalciferol) from 7-dehydrocholesterol, when synthesized in the skin
Where do we get vitamin D from?
Found naturally in a few foods but is photosynthesized in the skin
Is vitamin D requirement increased during pregnancy?
- Quantities of 25(OH)D transferred to fetus are small
- Do not affect overall vitamin D status of pregnant women
What is the function of vitamin E?
- A specific role for vitamin A in a required metabolic function has not been found
- Major function: non-specific chain-breaking antioxidant preventing the propagation of lipid peroxidation
What is the vitamin E RDA based on?
- Induced vitamin E deficiency in humans
- Correlation between H2O2-induced erythrocyte lysis and blood [alpha-tocopherol]
What is the difference between tocopherols and tocotrineols?
Tocotrienols have an unsaturated side chain
What is synthetic vitamin E?
Esters of either RR- or synthetic mixture of all racemic forms
What is the RDA of alpha-tocopherol?
What are plasma [vitamin E] dependant on?
Dependant on the affinity of hepatic alpha-tocopherol transfer protein (a-TTP)
What sterioisomeric forms of vitamin E are used to estimate the requirement?
2R-stereoisomeric forms are used to estimate the requirement
Why are other forms not used to estimate the requirement?
The 2S-stereoisomeric forms, the other tocopherols and the tocotrienols fail to bind with a-TTP and are therefor not used to estimate the requirement
What is hemolytic anemia caused by?
Vitamin E deficiency in premature newborns
How can vitamin E deficiency in premature newborns be combated?
- No evidence that maternal supplementation would prevent deficiency symptoms in premature newborns
- Supplementation of pregnant females appears to be unwarranted
What is the function of vitamin K?
During the synthesis of the biologically active form of a number of proteins involved in blood coagulation and bone metabolism
What is the vitamin K AI based on?
Based on representative dietary intake data from healthy individuals
What is the major form of vitamin K in the diet?
What are menaquinones?
Form of vitamin K produced by bacteria in the lower bowel
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