NAD supplements do not cross the blood-brain barrier. Any article that suggests NAD or NAD+ is helpful is suspect.
Actually, they do, but normal nicotinamide riboside does not cross well.
Liposome-based loading enhances the distribution of nicotinamide riboside chloride into the brain and its neuroprotective effects in cerebral ischemic mice
https://www.sciencedirect.com/science/article/pii/S2324242624000184
NMN crosses:
Nicotinamide Mononucleotide Adenylyltransferase 1 Regulates Cerebral Ischemia–Induced Blood–Brain Barrier Disruption Through NAD+/SIRT1 Signaling Pathway
https://link.springer.com/article/10.1007/s12035-022-02903-6