Vitamin A is a name for a group of fat-soluble compounds including retinol, retinal and retinyl esters
The two different forms of vitamin-A are preformed vitamin A and provitamin A carotenoids. Both are converted in the body to retinol which is oxidized to retinal and finally to retinoic acid. Measuring plasma retinol levels indicates the vitamin-A status in the body.[1,3]
Of the two vitamin A forms, only provitamin A is found abundantly in plant-based diets and beta-carotene is one of the most important provitamin carotenoid followed by alpha-carotene and beta-cryptoxanthin. 
Observational studies have found a correlation between excess preformed vitamin-A intake and increased fracture risk as well as irreversible liver damage in some cases.[1,2] However, beta-carotene is not known to be toxic, even with large supplemental doses [1,2].