Dietary Reference Intakes
What Dieticians Need to Know
Dietary Reference Intakes
• examples: vitamin C and calcium
DRI Process
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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
Components of the DRIs
• Four values instead of one
• These are:
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EAR: Estimated Average Requirement
RDA: Recommended Dietary Allowance
AI: Adequate Intake
UL: Tolerable Upper Intake Level
• How derived? How Interpreted?
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
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
Energy RDA =EAR
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
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)
Nutrients Recognized as Toxic
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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)
Examples to Illustrate DRIs
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Vitamin C
Has an EAR
Has an RDA
Has a UL
Important yet not
much is known
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Calcium
No EAR
Has an AI
Has a UL
Important but
controversial
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
EAR and RDA for Vitamin C
• EAR = 75 mg for adult men
60 mg for women
• Based on following study:
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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
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 =>
75 mg, as level of “adequate” vitamin C
levels in WBCs
How do we assess Vitamin C
adequacy?
• Find usual intake of vitamin C in population
• The percent of the pop’n whose intakes are
below EAR = % at risk for inadequacy
• In following figure, North Americans have
some risk of inadequacy:
– ~ 10-20% ingesting too little
Vitamin C RDA
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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
Vitamin Toxicity
• Many “problems” attributed to vitamin C
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Excess oxalate, uric prodn  kidney stones
Pro-oxidant
 Fe absorption  iron overload
 B12
Rebound scurvy
• DRI panel found no evidence for anything
except GI disturbances (osmotic diarrhea)
UL for Vitamin C
• Uncontrolled cases and several controlled
studies show that some people get GI
disturbances at >3 g
• 3 g = LOAEL
• Since UL is set so no risk of adverse effects,
Then UL = 3/1.5 = 2 g (~ NOAEL)
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
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 > 1000 mg
• Account for less absorption at 50+
• Value set at 1200 mg
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