IMHO, Sinclair is making a mistake by taking spermidine directly since it will probably deplete riboflavin (B2) because the excess spermidine will be metabolized my Spermine oxidase which uses B2 as a cofactor

https://www.uniprot.org/uniprotkb/Q9NWM0/entry

IMO, a better way is to trigger your own body to make spermidine by getting enough Arginine and taking Manganese, B6, and keeping your methylation cycle flowing.

The pathway is as follows:

Arginine -> (Arginase, uses manganese as a cofactor) -> Ornithine -> (Ornithine decarboxylase, uses B6 as a cofactor) -> putrescine -> (Spermidine synthase which needs SAMe and Pyruvate) -> Spermidine

https://www.mdpi.com/metabolites/metabolites-12-00344/articl...