Ascorbic acid has two enantiomers. Only one of them is “vitamin C”. I’m not sure if this is what she’s referring to, though.

In another interview (in French, sorry), when talking about beta-carotene, she says that a substance isolated from its natural environment (other molecules, cells, etc.) and replaced with a pure, synthetic version could have very different biological properties.

Honestly, I think we still know very little about this. This research is about strong statistical associations. A lot more research is needed to understand the exact biological processes.

Here’s the press release from INSERM, which is likely a better source: https://presse.inserm.fr/en/colorants-conservateurs-trois-nouvelles-etudes-pointent-des-liens-entre-additifs-alimentaires-et-risque-accru-de-cancer-de-maladies-cardiovasculaires-et-dhypertension/72881/