Have gastrointestinal conditions that impair nutrient absorption (e.g., IBS, celiac disease, or Crohns)
Eisenberg T, Knauer H, Schauer A, Bttner S, Ruckenstuhl C, Carmona-Gutierrez D, Ring J, Schroeder S, Magnes C, Antonacci L, Fussi H, Deszcz L, Hartl R, Schraml E, Criollo A, Megalou E, Weiskopf D, Laun P, Heeren G, Breitenbach M, Grubeck-Loebenstein B, Herker E, Fahrenkrog B, Frhlich KU, Sinner F, Tavernarakis N, Minois N, Kroemer G, Madeo F (2009) Induction of autophagy by spermidine promotes longevity
They cannot bind to receptors properly, cannot be absorbed efficiently, and in some cases can provoke unwanted immune responses
This bidirectional interaction enables restoration of normal NO balance critical for proper sphincter timing