I am struck by the second of those two charts, which appears to indicate that two tablets of Mg glycerophosphate produces a very similar serum increase (AuC) as a single one. Any thoughts as to why that might be? Something like serum levels above a certain point causing sequestration in bones? Or possibly enterocytes unable to absorb past a certain concentration?

Nothing earth shattering, just something that popped out at me.

BTW, I looked at the in-vivo methods section of the linked study. Many thanks for linking to one with open access! Crossover design looks good - although the number of test subjects is quite limited and I'm a bit puzzled as to why they thought it necessary to use Bonferroni correction against what appeared to be a single hypothesis. Probably just an indication that I'm a amateur.