Dietary Reference Intakes

What Dieticians Need to Know

Dietary Reference Intakes

• examples: vitamin C and calcium

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

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?

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

• 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

•

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

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: – 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

• 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 – Excess oxalate, uric prodn  – Pro-oxidant – –   Fe absorption B12  – Rebound scurvy kidney stones iron overload • 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