@haidut , what are your thoughts on Chris Masterjohn's take that regular plain riboflavin is superior to R5P:
"I have, for years, believed that riboflavin 5’-phosphate (aka, flavin mononucleotide or FMN) supplements are better than plain old riboflavin, especially for people who are hypothyroid or have low adrenal status, since these conditions impair the activation of riboflavin to it’s 5’-phosphate form. After doing the research for this podcast I now believe that for healthy people it makes no difference and that for people with small intestinal pathologies, the cheaper, less fancy, plain old “riboflavin” is likely to be more effective."
"they (plain riboflavin and R5P) are both equal in every context studied (making it pointless to use R5P if it is more expensive, and making calling it “activated” total marketing BS).
However, the enzymes needed for hydrolyzing the P are brush border enzymes. The brush border is known to be assaulted in small intestinal disease. So it makes sense that R5P might have poor absorption in small intestinal diseases that damage the brush border."
I agree that for young, healthy people using plain riboflavin may be sufficient. But even in those people I would not say there is "no difference" between the two. Try 50mg dose of each on separate days and you will see if they work the same.