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OCR for page 485
PART IV: APPENDIX H 485 H STANDARD DEVIATION OF REQUIREMENTS FOR NUTRIENTS WITH AN EAR Standard Deviation (SD) of requirements is calculated from the Coefficient of Variation (CV) and the Estimated Average Requirement (EAR) as: SD = CV ¥ EAR Basis if not 10 percenta Nutrient with an EAR CV (percent) MACRONUTRIENTS Dietary Carbohydrate 15 Variation in brain glucose utilization Protein 12 Skewed distribution; calculated as half distance from 16th to 84th percentile of protein requirement distributionb VITAMINS Vitamin A 20 Half-life for liver vitamin A in adults Vitamin B6 10 Vitamin B12 10 Vitamin C 10 Vitamin E 10 Folate 10

OCR for page 485
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 486 Basis if not 10 percenta Nutrient with an EAR CV (percent) Niacin 15 Limited studies suggest greater variation than 10 percent, partly from wide variation in conversion efficiency of tryptophan to niacin Riboflavin 10 Thiamin 10 MINERALS Copper 15 Limited data to set EAR Iodine 20 Calculation that subtracts out variation due to experimental design Iron Skewed distribution; calculated by modeling components of requirement distribution, estimating the requirement for absorbed iron at the 97.5 percentile, and with use of an upper limit of 18 percent iron absorption, and rounding Magnesium 10 Molybdenum 15 Limited data to set EAR (few Mo levels in depletion/repletion study and small number of subjects) Phosphorus 10 Selenium 10 Zinc 10 a The assumption of 10 percent is based on extensive data on the variation in basal metabolic rate and on a similar CV of 12 percent for protein requirements in adults. b Rand and colleagues demonstrated that the natural logarithm of requirements in mg nitrogen/kg/day has a normal distribution with a mean of 4.65 and a standard devia- tion of 0.12. From this and because the skewness is not extreme, an approximate stan- dard deviation can be calculated.