An Experimental Determination of the Minimum Vitamin A Requirements of Normal Adults

The Occurrence of Abnormal Dark Adaptation and Its Relation to Vitamin a Metabolism in Patients With Cirrhosis of the Liver

“…After a 4-minute exposure to white light 4700 millilamberts, the first phase (a) of cone adaptation takes place, to be followed by the rod phase (b). If the normal person is subjected to a diet low in vitamin A for a sufficient length of time, the final threshold becomes raised not only for the rods but also for the cones (20,21,22). The cone changes were noted originally in cases of liver cirrhosis (14).…”

Absorption and retinol equivalence of β-carotene in humans is influenced by dietary vitamin A intake

“…Using functional indicators, the earliest investigations into the vitamin A value of ␤ -carotene estimated that between 2 g to 4 g of ␤ -carotene were needed to have the same biological efficacy (i.e., vitamin A activity) as 1 g of retinol (16)(17)(18). In terms of molar vitamin A value, this is equivalent to 0.47 mol to 0.94 mol retinol formed from 1 mol ␤ -carotene.…”

Retinol Equivalency Ratio of β-Carotene

“…Another study observed the beginning of decline of dark adaptation after 3 mo of being fed a vitamin A-deficient diet (5). Because of the short duration of onset, the status of dark adaptation was judged to be questionable in the study by Booher et al (4), and therefore was not considered to be reliable for evaluating the correction of dark adaptation with vitamin A or ␤-carotene.…”

“…After eliminating these two studies (4,5), two other studies remained for considering vitamin A activity of ␤-carotene in oil (3,6). In the study by Hume and Krebs (6), correction of abnormal-dark adaptation was successfully measured following a single dose of either vitamin A or ␤-carotene given to two individuals.…”