Dietary Reference Intakes What Dieticians Need to Know

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 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 urinary oxalate excretion, increased uric acid excretion in urine kidney stones – Pro-oxidant – Fe absorption iron overload – serum B 12 – 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 = 5 g/2 = 2. 5 g