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The Vitamin a Content of Human Blood Plasma as an Index of Carotene Utilization¹

Two Figures

Nutrition Department, Hawaii Agricultural Experiment Station, Honolulu, Hawaii

A single subject was placed on a vitamin A-low diet for 3 periods of 166, 80 and 115 days, respectively. Between these 3 periods were 2 periods of moderate vitamin A intake of 73 and 163 days, respectively.

The level of carotene in the plasma dropped rapidly each time the change was made to the vitamin A-low diet. The vitamin A level, on the other hand, did not show any significant change for 140 days, then dropped very gradually over a long period of time and finally made a rather abrupt drop. This drop was taken to indicate the end of the depletion period. The plasma levels were 149 µg carotene and 133 I.U. vitamin A per 100 ml when the experiments began and 15 µg carotene and 76 I.U. vitamin A per 100 ml at the end of the depletion period.

The feeding of increasing amounts of vitamin A (distilled esters in oil) resulted in a gradual increase in the vitamin A level in the plasma. An intake of 3500 I.U. per day maintained a level of 100 to 110 I.U. per 100 ml in the plasma and was taken to be a satisfactory intake for maintenance for this subject. Amounts of papaya which, according to chemical assay, provided 3500 I.U. of vitamin A activity per day in the form of carotenoids were then fed for 28 days. The plasma level of vitamin A was maintained between 100 and 120 during this period showing that the carotenoids of the papaya were well-utilized by this subject. Cryptoxanthin contributed 80% of the estimated vitamin A activity of the papaya samples.

These results show that the plasma level of vitamin A can be used as a measure of the utilization of carotenoids by human beings. The data obtained, however, do not indicate that the blood plasma level is more sensitive than the dark adaptation time as an index of vitamin A nutrition, although it is undoubtedly a more specific measure.

² Present address, Department of Agricultural and Biological Chemistry, The Pennsylvania State College, State College, Pennsylvania.

Manuscript received 8 April 1948.