ABSORPTION OF CAROTENE IN MAN AS OBSERVED FROM THE INCREASE OF SERUM VITAMIN A AND CAROTENE LEVELS

1. Various quantities of β-carotene and vitamin A palmitate were given orally in a healthy male subject and changes in serum vitamin A and carotene levels were investigated. The maximal rise in vitamin A level after ingesting β-carotene was 25% of that after ingesting vitamin A of the same I. U.2. The changes in serum vitamin A and carotene levels were examined successively after ingesting various quantities of cooked squash and the rise in the highest vitamin A and carotene levels was compared with those obtained after ingesting β-carotene in oil. For a rise in serum vitamin A level equal to that obtained with β-carotene in oil, 2.1-2.8 times the amount of carotene in squash was required. For a rise in serum carotene level equal to that of β-carotene in oil, 1.4-2 times as much carotene in squash was required.3. Similar experiments with the carrot showed that 3 times as much carrot was required as β-carotene in oil for an equal rise in serum vitamin A levels and twice as much carotene in carrot was required for an equal rise in serum carotene levels.4. Similar experiments with spinach showed that 1.8 times as much carotene in spinach was required for a rise in serum vitamin A level and twice as much carotene in spinach was required for a rise in serum carotene level equal to that of pure β-carotene solution.5. From these findings, it is assumed that the absorption of the carotene in food is 31 to 55% that of β-carotene in oil in man and this coincides well with the absorption rate estimated from the carotene in food and in the feces, suggesting an insignificant decomposition of carotene in the digestive tract.6. Though almost all of the β-carotene in oil is absorbed, the increase in serum vitamin A level is about 1/3 that occurring with vitamin A palmitate, so that 6 times as much I. U. of carotene in food must be taken as vitamin A in order to obtain an equal effect. However, a rise in serum carotene level also takes place after ingesting β-carotene. Considering this fact, the effect of β-carotene may be greater than 1/3 of vitamin A of the same I. U., but possibly less than 1/2. The effect of the carotene in food is considered to be at most 1/4 that of vitamin A.