Table 1.

Review of the total liver vitamin A (VA) reserve as it relates to the dietary reference intake (DRI) criteria used to formulate estimated average requirements and to biomarkers of VA and carotenoid status.

DRI criteria	Total liver VA reserve µmol/g	Model	References
(1) No clinical signsXerophthalmic sequelae	<0.02	Predicted for children	Olson8*
(2) Adequate plasma retinolDepressed serum retinolconcentrations	>0.005<0.02<0.01<0.1	RatsPredicted for childrenGerbilsAdult humans	Lewis et al.,28 High et al.,29 Riabroy et al.30Olson8*Kaeppler et al.31Olsen, Suri et al.7
(3) Induced biliary excretionEnhanced biliary secretion or excretion	>0.1	Rats	Hicks et al.4Varma and Beaton35
(4) Protection for 4 monthsmRNA upregulation of LRAT	>0.1	Rats	Zolfaghari and Ross21
Biomarkers of VA status
Positive dose response tests	<0.10	Piglets, calves, rats, humans	Sheftel and Tanumihardjo45*
Elevated provitaminA carotenoids	>0.7 >1	Gerbils (liver) Humans (serum)	Tanumihardjo19*Sowa et al.61Mondloch et al.62
Elevated serum retinyl esters	∼3	Humans	Olsen, Suri et al.7
Retinol isotope dilution	Continuum	RatsNon-human primatesHumans	Tanumihardjo68 Escaron et al.69Tanumihardjo et al.2*Tanumihardjo19*
Hepatic biopsy	Continuum	Humans	Olsen, Suri et al.7

^*These references are either a chapter in a book or reviews of multiple studies.