1. Dietary Reference Intakes
What Nutritionists and Other Health Professionals Need to Know

2. Dietary Reference Intakes
examples: vitamin C and calcium

4. 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

5. 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?

7. EAR and RDA values EAR RDA = EAR + 2 SD
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

9. 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

10. Energy RDA =EAR

11. 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

12. 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)

13. 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)

15. 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

16. Vitamin C Many functions: In cells   plasma  urine excretion
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

17. 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

18. 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

20. 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

22. Vitamin C RDA Use RDA as a goal for an individual RDA = EAR + 2 SD
Men: RDA = (7.5) = 90 mg
Women: RDA = (6) = 75 mg (rounded)
Smokers – need more
Add 35 mg to RDA

23. Vitamin Toxicity Many “problems” attributed to vitamin C
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)

24. 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)

25. 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

26. AI for Calcium
Age 19-30: retain 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

27. 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