>> individuals with common, functional genetic polymorphisms related to glutathione levels

That would be the GSTM1 and GSTT1 SNPs. There's evidence that they're connected with higher risk for several cancers (breast, nasopharyngeal, probably others).

It's one of the reasons I consume broccoli sprouts (good source of isothiocyanates that can activate NRF2) Dr Jed Fahey at Hopkins has done a number of studies showing it can trigger excretion of toxins (some heavy metals, benzene).

As a side note, if you're taking NAC, I've seen studies showing very positive results for elders taking GlyNAC (glycine and NAC). Collagen's a good source of glycine, although it also has some isoleucine (I've seen a couple of studies showing that intake of that should be kept low).

Just a thought...