Dietary Reference Intakes

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Dietary Reference Intakes

• What Dieticians Need to Know

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Dietary Reference Intakes

• examples vitamin C and calcium

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DRI Process

• North American Initiative
• Institute of Medicine and Health Canada
• Each panel has at least 1 Canadian
• Canadians review draft document
• Intended to replace 1989 RDAs and 1990 RNIs
• Not just traditional nutrients

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Components of the DRIs

• Four values instead of one
• These are
• EAR Estimated Average Requirement
• RDA Recommended Dietary Allowance
• AI Adequate Intake
• UL Tolerable Upper Intake Level
• How derived? How Interpreted?

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EAR and RDA values

• EAR
• obtain scientific data to estimate the average
  requirement for a nutrient
• Add 2 SD to this value so that 98 of popn has
  their requirement met
• Resulting value is RDA
• RDA EAR 2 SD

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EAR and RDA (cont)

• In preceding diagram, EAR set at 45 units
• RDA is 63 units
• Therefore, RDA EAR 2(9)
• MOST nutrients RDA EAR 2(10)
• Can be written as RDA EAR x 1.2

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Energy RDA EAR
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Use of DRIs

• Apply to healthy people
• RDA is generous covers 98 of popn
• Compare to usual (average) intake, not intake on
  any given day
• RDA is goal for an individual
• EAR used to assess groups

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Nutrients Without an EAR Do Not Have RDA

• Need scientific studies to determine EAR
• Nutrients without EAR do not have an RDA
• Instead given an AI
• Used as goal for individual ( RDA)
• We cannot assess groups using an AI
• Calcium, Vitamin D, Fluoride, Biotin, Pantothenic
  acid (and all infant values)

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Nutrients Recognized as Toxic

• UL value assigned to many nutrients
• Often based on case reports, not studies
• Value at UL has no risk
• Risk increases with higher intake
• sustained intake not a single dose (except Mg)

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Examples to Illustrate DRIs

• Vitamin C
• Has an EAR
• Has an RDA
• Has a UL
• Important yet not much is known

• Calcium
• No EAR
• Has an AI
• Has a UL
• Important but controversial

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Vitamin C

• Many functions
• Enzyme cofactor for collagen synthesis
• Involved in synthesis of hormones,
  neurotransmittors
• Now recognized as important anti-oxidant
• Increases Fe absorption
• In cells ? ? plasma ? urine excretion
• ? in specialized tissues WBCs

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EAR and RDA for Vitamin C

• EAR 75 mg for adult men
• 60 mg for women
• Based on following study
• 7 healthy men lived in for 6 months
• Fed low C diet (5 mg/d) until depleted
• Given graded doses until steady state reached
• Measured serum, neutrophil, and urine ascorbate

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EAR for Vitamin C

• At 100 mg, neutrophils were saturated with
  acorbate in 4/7 subjects, but urine excretion was
  high (25 of dose)
• At 60 mg, neutrophils were not quite saturated,
  but urine excretion 0
• Panel chose value between 60 and 100 gt 75 mg, as
  level of adequate vitamin C levels in WBCs

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How do we assess Vitamin C adequacy?

• Find usual intake of vitamin C in population
• The percent of the popn whose intakes are below
  EAR at risk for inadequacy
• In following figure, North Americans have some
  risk of inadequacy
• 10-20 ingesting too little

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Vitamin C RDA

• Use RDA as a goal for an individual
• RDA EAR 2 SD
• Men RDA 75 2(7.5) 90 mg
• Women RDA 60 2 (6) 75 mg (rounded)
• Smokers need more
• Add 35 mg to RDA

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Vitamin Toxicity

• Many problems attributed to vitamin C
• Excess urinary oxalate excretion, increased uric
  acid excretion in urine ? kidney stones
• Pro-oxidant
• ? Fe absorption ? iron overload
• ? serum B12
• Rebound scurvy
• DRI panel found no evidence for anything except
  GI disturbances (osmotic diarrhea)

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UL for Vitamin C

• Uncontrolled cases and several controlled studies
  show that some people get GI disturbances at gt3 g
• 3 g LOAEL
• Since UL is set so no risk of adverse effects,
• Then UL 3/1.5 2 g ( NOAEL)

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Calcium

• Panel chose desirable daily calcium retention
  as criterion for setting AI
• Retention is classically measured as calcium
  balance (Intake Losses) assume what is
  retained is in bones
• Now, can directly measure bone mineral content
  BMC mineral in bone

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AI for Calcium

• Age 19-30 retain 10-50 mg/day, estimate 957 mg
  intake from old balance studies
• Judge 1000 mg to be appropriate
• At older ages (50) clinical trial data shows
  less bone loss at intakes gt 1000 mg
• Account for less absorption at 50
• Value set at 1200 mg

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UL for Calcium

• Whiting and Wood compiled case reports of
  milk-alkali syndrome in 1995 (NR 97)
• Other problems of excess Ca kidney stones, ?
  iron absorption, ? Zn retention
• LOAEL 5 g (in otherwise healthy)
• UL 5g/2 2.5 g