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1.
Effects of vitamin B12 on the utilization of carotene and vitamin A by the rat.
>The rats which received vitamin B12 grew about 50 per cent. more than those which did not, and the deposition in the liver of vitamin A from the carotene given was 37 per cent. greater.
https://www.cabdirect.org/cabdirect/abstract/19541400318
http://mbbsdost.com/Effects-vitamin-B12-utilization-carotene-vitamin-A-by-rat-The-Journal-nutrition-HIGH-EG-WILSON-EG--1953-Jun/pubmed/809974
2.
Interaction of ethanol with beta-carotene: delayed blood clearance and enhanced hepatotoxicity.
>On cessation of beta-carotene treatment, plasma levels decreased more slowly in the alcohol-fed baboons than in the controls. Percutaneous liver biopsy specimens revealed that liver concentrations of beta-carotene correlated with plasma levels but were higher in the alcohol-fed baboons than in the control baboons, whereas the beta-carotene-induced increase in liver retinoids was lower
https://www.ncbi.nlm.nih.gov/pubmed/1568731
3.
Effects of purified dietary fiber sources on β-carotene utilization by the chick
>Results of expt. 1 showed that hemicellulose, lignin and citrus pectin, but not arenaceous flour or polygalacturonic acid, depressed β-carotene utilization by the chick, as measured by percentage of consumed β-carotene stored in liver as vitamin A relative to the 0% fiber control.
https://www.ncbi.nlm.nih.gov/pubmed/3027282
4.
Protein quality and carotene utilization.
>The results show that both amount and quality of protein in the diet affect conversion of carotene to vitamin A, a fact which may be important in countries where carotene is the main source of vitamin A and amount and quality of protein in the diet are low
https://www.cabdirect.org/cabdirect/abstract/19631400290
5.
THE EFFECT OF THYROID ON THE CONVERSION OF CAROTENE INTO VITAMIN A*
>That the thyroid gland might be involved in the metabolism of carotene was first suggested by von Noorden in 1907 […] Laboratory studies have likewise pointed toward the conclusion that a functioning thyroid gland is necessary for the animal to convert carotene into vitamin A.
http://www.jbc.org/content/171/2/513.full.pdf
6.
Plasma retinol levels and side effects following high-dose retinyl acetate in breast cancer patients.
>We concluded that the daily dose of 300,000 I.U. retinyl acetate can be administered to cancer patients over a period of several months, is well tolerated and yields a substantial increase of systemic retinol.
https://www.ncbi.nlm.nih.gov/pubmed/3218964
Oral vitamin A in acne vulgaris. Preliminary report.
>Retinol was highly efficacious in doses of 300,000 units for women and 400,000 to 500,000 units for men, toxicity was slight and limited mainly to skin (xerosis) and mucous membranes (cheilitis). The danger of hypervitaminosis A in this dosage range has been exaggerated.
https://www.ncbi.nlm.nih.gov/pubmed/6453848
7. http://nutritiondata.self.com/facts/beef-products/3469/2