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DRI Dietary Reference Intakes: For Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline
flow, but in the studies cited above, all urine was collected over a period of 48 to 72 hours.
In a group of East Indian men aged 27 to 47 years with a mean EGRAC of 1.53, short periods of increased physical activity while on a diet providing riboflavin at 0.42 mg/1,000 kcal for 16 days led to an increase in EGRAC. When riboflavin status is marginal, increased physical activity may be more likely to lead to further deterioration as assessed by EGRAC, and values may not return to baseline after the extra exercise segment of the study is completed (Soares et al., 1993). However, the energy cost of the exercise and a measure of mechanical efficiency remained stable throughout.
A number of studies have failed to show an improvement in work performance (Powers et al., 1987; Prasad et al., 1990; Tremblay et al., 1984; Weight et al., 1988) and endurance (elderly subjects) (Winters et al., 1992) with riboflavin supplementation even when subjects were described as subclinically deficient (having lower-than-normal ranges of biochemical indices but no clinically observable signs of deficiency).
It is possible that the riboflavin requirement is increased for those who are ordinarily very active physically (e.g., athletes or those who carry heavy packs much of the day), but data are not available on which to quantify the adjustment that should be made.
Although a number of reports indicate that women taking high-dose oral contraceptives have impaired riboflavin status, no difference was seen when dietary riboflavin intake was controlled (Roe et al., 1982).
APPROACHES FOR DERIVING THE ESTIMATED AVERAGE REQUIREMENT
Primary: Maintenance or Restoration of Riboflavin Status by Using Biochemical Indicators
To derive the Estimated Average Requirement (EAR) for adults, more weight was given to experimental studies that included information on response to diets in which the source of riboflavin was food or food plus supplemental riboflavin (Table 5-1). Studies that used more than one indicator were considered most useful, especially if a functional assay (e.g., EGRAC) was conducted along with measurement of erythrocyte or urinary riboflavin. However, the