1 Ten healthy female volunteers were given 5 doses of retinol as the palmitate; 50 and 150 mg retinol as an oral supplement, 50 and 150 mg as fried calf liver (50 and 150 g) and 3, 9 or 30 mg by intra-muscular injection.
2 Plasma concentrations of retinyl palmitate were higher after 50 mg retinol given as an oral supplement compared with 50 mg as liver; there was no significant difference between the 150 mg doses. Plasma concentrations of retinol showed only small increases.
3 The peak plasma concentrations (Cmax) of all-trans-retinoic acid, the principal teratogenic metabolite of retinol, and the area under the concentration-time curve (AUC) were up to 20-times higher after supplements compared to the same dose as liver. Plasma concentrations of all-trans-4-oxo-retinoic acid, 13-cis-retinoic acid and 13-cis-4-oxo-retinoic acid showed smaller differences between supplements and liver.
4 Intra-muscular administration of 30 mg retinol gave retinyl palmitate concentrations similar to those found after the oral doses but did not increase circulating concentrations of the acid metabolites.
5 Based on the formation of all-trans-retinoic acid, liver and supplements are not of equivalent teratogenic potential. Advice to pregnant women on the consumption of liver based on the reported teratogenicity of vitamin A supplements should be reconsidered.