Orally ingested ubiquinol-10 or ubiquinone-10 reaches the intestinal tract and is absorbed by the small intestine of mice mostly in its original form.

Coenzyme Q10 (CoQ10) is an important lipid-soluble antioxidant and an essential component of the mitochondria. The oral bioavailability of the reduced form of CoQ10, ubiquinol-10, has been reported to be greater than that of the oxidized form of CoQ10, ubiquinone-10, in some studies. In contrast, it has also been highlighted that the oral bioavailability of ubiquinol-10 is not superior to that of ubiquinone-10 because ubiquinol-10 may be oxidized during digestion. In fact, it has not been shown which form of CoQ10 exists in the process from oral intake to absorption in the gastrointestinal tract. In this study, the amounts of ubiquinol-10 and ubiquinone-10 were measured in the gastrointestinal content and small intestine tissue after oral administration of ubiquinol-10 or ubiquinone-10 to C57BL/6J mice. The form of CoQ10 detected in the gastrointestinal content and small intestine tissue was almost the same as that when administered orally. The results of our study suggested that the orally administered ubiquinol-10 and ubiquinone-10 mostly reached the small intestine without oxidizing to ubiquinone-10 and reducing to ubiquinol-10, and both were absorbed by the small intestine tissue in almost their original forms.