Why would an author refer to 25(OH)D and 25(OH)D3 as 1 in the same to refer to blood levels of vitamin D?

I understood ingested D2 and D3 are reflected by 25(OH)D and do not understand why this paper uses 25(OH)D3 to refer to cumulative blood levels of vitamin D.

05 September 2021 1,014 4 View