2022; Zingone et al. 2023). Copper and C, B1, and B6 vitamins deficiencies can also decrease DAO activity (Shulpekova et al. 2021). DAO activity can also be affected by the menstrual cycle (Hrubisko et al. 2021) and by some diseases, including migraines, atopic dermatitis, irritable bowel syndrome, cyclic vomiting syndrome, and muscular pain (Worm et al. 2019; Hrubisko et al. 2021). Here, DAO is linked to irritable bowel syndrome.