Vitamin A is a name for a group of fat soluble compounds including retinol, retinal and retinyl esters
The two 2 different forms of vitamin-A, preformed vitamin A and provitamin A carotenoids converts to retinol and total body stores of retinol indicate the vitamin-A status in the body.[1,3]
However, to support the important biological functions, retinol further needs to oxidized to retinal and then to retinoic acid. 
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 corelation 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].