What is Coenzyme Q10 (CoQ10)?

What is Coenzyme Q10?

Coenzyme Q10 (CoQ10) is a fat-soluble compound synthesized in the mitochondrial inner membrane that serves two critical functions: it acts as an essential electron carrier in cellular energy (ATP) production and functions as the only endogenously synthesized lipid-soluble antioxidant in the human body. 1

Chemical Structure and Nomenclature

• CoQ10 is also called "ubiquinone" due to its quinone chemical structure and ubiquitous presence in virtually all cells in the human body 1
• The "Q" refers to the quinone chemical groups and the "10" refers to the number of isoprenyl subunits in its tail 1
• It exists in both reduced (ubiquinol) and oxidized (ubiquinone) forms in cell membranes and mitochondria 2

Primary Biological Functions

Energy Production

• CoQ10 plays a fundamental role in mitochondrial bioenergetics as an electron and proton carrier, specifically mediating electron transport from complex I or II to complex III in the respiratory chain 1
• It is crucial in tissues with high energy requirements, particularly the heart, skeletal muscles, kidneys, liver, and brain 1

Antioxidant Protection

• CoQ10 is present in all cellular membranes, high- and low-density lipoproteins, and mitochondria, protecting them against toxic effects of free radicals generated during normal cellular metabolism 1
• It helps regenerate vitamin E to its antioxidant form 1
• The reduced form (ubiquinol) and ubisemiquinone radical possess antioxidant properties that prevent oxidative modifications of proteins, lipids, and DNA 3

Additional Functions

• Gene regulation of overall tissue metabolism 1
• Neuroprotection by inhibition of glutamate release and calcium influx 1
• Possible immunomodulation 1

Synthesis and Sources

Endogenous Production

• CoQ10 is predominantly synthesized de novo in the human body at an estimated rate of 500 mg/day 1, 4
• Endogenous biosynthesis tends to decline with age 1
• It is synthesized from several components including mevalonate, tyrosine, riboflavin, folate, B12, and vitamin C 1

Dietary Sources

• Average daily nutritional intake is only 3-6 mg/day 1, 5
• The richest nutritional sources are meat, fish (particularly heart, chicken leg, herring, and trout), nuts, and some oils 1, 6
• Much lower levels are found in most dairy products, vegetables, fruits, and cereals 6

Absorption and Transport

• Intestinal absorption of CoQ10 is inherently low due to its hydrophobicity and large molecular weight 1, 5
• Absorption is slow, with peak plasma levels occurring 5-10 hours after ingestion 1, 5
• CoQ10 is transported in plasma by low-density lipoproteins (LDL), making plasma levels dependent on lipoprotein status 1, 5
• Taking CoQ10 with fat-containing meals significantly enhances absorption given its lipid-soluble nature 5

Clinical Significance of Deficiency

Symptoms of Deficiency

• Sore, aching muscles and muscle weakness 1, 4
• Fatigue and mental confusion 1
• Gingivitis 1
• Elevated blood pressure and high cholesterol levels 1
• Seizures, vision and/or hearing loss, and kidney damage 1

Conditions Associated with Reduced Levels

• CoQ10 levels can be reduced by aging, genetic factors, and certain drugs (particularly statins) 2
• Decreased levels are observed in many pathologies including cardiac disorders, neurodegenerative diseases, AIDS, and cancer 3
• CoQ10 deficiency has been implicated in patients with cardiometabolic disorders 1

Supplementation Considerations

Available Forms

• CoQ10 is commercially available as either ubiquinol (reduced form) or ubiquinone (oxidized form) 1
• No IV formulation currently exists 1, 5

Dosing Range

• Studies have used doses ranging from 50-1200 mg in adults, with up to 3000 mg/day being well-tolerated 1, 4
• For children, doses up to 10 mg/kg/day have been studied 1
• No DRI (Dietary Reference Intake) or RDA (Recommended Dietary Allowance) has been established 1, 7

Safety Profile

• CoQ10 supplementation appears remarkably safe with minimal side effects even at very high doses 1, 7
• The most common adverse effects are mild gastrointestinal symptoms including nausea, vomiting, diarrhea, and anorexia 1, 7
• Monitoring liver enzymes is recommended during supplementation, particularly at higher doses or with prolonged use 7

Important Drug Interaction

• CoQ10 may increase warfarin metabolism through selective interaction with cytochrome P450 enzymes, though clinical evidence suggests that 100 mg/day has no effect on warfarin's clinical action 7
• The recommendation is to avoid CoQ10 or monitor INR more frequently if supplementation is necessary, particularly at doses above 100 mg/day, for patients on warfarin 7

Clinical Applications

• While supplementation studies have been carried out in a variety of conditions, they have generally shown little benefit across various conditions according to the ESPEN guidelines 1
• However, CoQ10 supplementation may be beneficial in specific scenarios including documented CoQ10 deficiency, chronic fatigue syndrome, mitochondrial dysfunction, and in patients on statins or other medications that deplete CoQ10 levels 4
• Benefits appear more consistent in diseased populations (chronic fatigue syndrome, mitochondrial disorders) than in healthy individuals 4