New aspects of the tolerance of retinol in humans.

A review is given of the evaluation of 517 cases of acute vitamin A intoxication and chronic hypervitaminosis A. Whereas acute vitamin A intoxication has lost numerical importance during the past 15 years, chronic hypervitaminosis-A, especially that caused by self-medication, has provoked world-wide discussion concerning the safety of retinol intake. Evaluation of the 132 cases of chronic hypervitaminosis-A showed that approximately one quarter cannot be considered as genuine cases, whereas the rest is divided almost equally between vitamin A prescription and self-medication. A significant positive correlation could be shown between the dose administered and the duration of treatment. Moreover, with comparable doses the symptoms of chronic hypervitaminosis-A appear significantly earlier (by a factor of 6) after emulsified or equivalent preparations than after oily emulsions because of their better absorbability. As soon as the liver vitamin A storage capacity is exhausted, hypervitaminosis-A symptoms appear and the liver vitamin A concentration is at least 10-fold the normal. The calculated vitamin A concentration in the liver of the individual cases of hypervitaminosis-A is highly correlated with the daily intake of vitamin A per kg of body-weight and its duration.