Ubiquinon

Ubiquinone, also called ubiquinon, is a lipid-soluble benzoquinone molecule that resides predominantly in cellular membranes, especially the inner mitochondrial membrane. It exists in several natural homologues, with ubiquinone-10 (CoQ10) being the most common form in humans. In its oxidized state it is ubiquinone and in its reduced state it is ubiquinol.

In cellular respiration ubiquinone serves as a key electron carrier within the mitochondrial electron transport chain. It shuttles electrons between complexes I and II to complex III, cycling between the oxidized and reduced forms as part of the electron transport process that drives ATP production. In addition to its role in energy production, ubiquinone acts as a lipid-soluble antioxidant in membranes. The reduced form, ubiquinol, can neutralize lipid peroxyl radicals and regenerate other antioxidants, such as vitamin E, helping protect membrane integrity.

Biosynthesis and natural occurrence: Ubiquinone is synthesized in human cells via the mevalonate pathway, with the isoprenoid side chain determining the variant (coenzyme Q range from Q9 to Q12 across species; humans predominantly have Q10). Levels of ubiquinone can decline with age, and deficiencies can be congenital (primary CoQ deficiency) or acquired; several drugs, including statins, may influence endogenous CoQ10 levels.

Dietary sources and supplementation: Ubiquinone is present in foods such as organ meats, fatty fish, and some vegetables and oils, though in relatively modest amounts. It is also available as a dietary supplement in oxidized (ubiquinone) or reduced (ubiquinol) forms, commonly at doses of 100–300 mg daily. Absorption is improved when taken with fat-containing meals.

Safety and regulation: Ubiquinone supplements are generally well tolerated, with rare gastrointestinal upset or rash. Interactions with anticoagulants such as warfarin have been reported, so medical guidance is advised. The evidence for disease-preventive benefits is mixed, and regulatory status treats CoQ10 mainly as a dietary supplement rather than a proven drug.