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 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

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: 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

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 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)

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