What is CoQ10, and how do ubiquinone and ubiquinol differ?

CoQ10 (coenzyme Q10, often just called Q10) is a fat-soluble substance that the body makes itself and that is found in all human cells. It comes in two main forms. Ubiquinone is the oxidised form, and ubiquinol is the reduced form, which carries two extra hydrogen atoms. The two are the same substance in different states. Meat, fish, nuts and some oils are the richest food sources.

In short:

• What it is: a fat-soluble substance the body makes itself, found in all human cells
• Where the name Q10 comes from: a tail of 10 isoprenoid units
• Two forms: ubiquinone (C59H90O4, 863.3 g/mol) and ubiquinol (C59H92O4, 865.4 g/mol), the same substance in two states
• From food: meat, fish, nuts and some oils; average intake is about 3–6 mg a day
• Watch out for: anyone on regular medication, pregnant or breastfeeding should ask a doctor or pharmacist before using it

What is CoQ10?

NCCIH, part of the US National Institutes of Health, says CoQ10 is a substance naturally present in the human body and that it is sold in the United States as a dietary supplement. Memorial Sloan Kettering says CoQ10 is found in all human cells and lists ubiquinone and ubidecarenone as other names for it.

What kind of substance is it?

The MeSH database of the US National Library of Medicine defines ubiquinone as a lipid-soluble benzoquinone that occurs in most aerobic organisms, from bacteria to higher plants and animals.

Why is it called Q10, and how does it differ from Q9?

According to PubChem, coenzyme Q10 is a ubiquinone with a side chain of 10 isoprenoid units. All ubiquinones share a 2,3-dimethoxy-5-methylbenzoquinone nucleus and differ in the length of the side chain. The "10" in Q10 is therefore the number of units in the tail.

Source: PubChem for every row. Each extra isoprenoid unit adds C5H8 to the formula and about 68 g/mol to the molecular weight. PubChem notes that ubiquinone-6 is found in baker's yeast (Saccharomyces cerevisiae). In food, a 1997 Danish study measured both coenzyme Q10 and Q9.

How do ubiquinone and ubiquinol differ?

They are not two different ingredients. They are the same CoQ10 in different chemical states. PubChem describes ubiquinol (CoQH2) as a reduced form of CoQ10 and classes ubiquinol-10 as a polyprenylhydroquinone: the core of the molecule changes from a quinone ring to a hydroquinone, while the tail stays the same.

Source: PubChem. The formulas differ by two hydrogen atoms (H90 against H92), and the molecular weights by about 2 g/mol.

Which form is in food?

The review by Pravst and colleagues (2010) says about half of the CoQ10 taken in from food is in the reduced form, so food contains both forms.

Why both names appear

Because the two are one substance in two states, the names ubiquinone and ubiquinol both refer to CoQ10. "Ubiquinone" is also the name of the whole family of compounds that CoQ10 belongs to, as ubiquinone-9, -8 and -6 in the table above show.

Does the body make CoQ10 by itself?

Yes. Memorial Sloan Kettering says all cells are capable of making CoQ10, and that it is not redistributed between organs through the blood. PubChem likewise notes that ubiquinol is not classed as a vitamin because humans make it themselves.

Which foods contain CoQ10?

A 2010 review by Pravst and colleagues of CoQ10 in foods (Critical Reviews in Food Science and Nutrition) says meat, fish, nuts and some oils are the richest dietary sources, while much lower levels are found in most dairy products, vegetables, fruit and cereals. The review also found large variations in CoQ10 content in some foods of different geographical origin.

Examples of amounts in food

A 2023 study by Semeniuc and colleagues in Foods measured CoQ10 in some raw materials and gathered values from other studies, for example:

Semeniuc and colleagues conclude that the CoQ10 content of fish is proportional to its fat content: mackerel and herring are fatty fish (more than 8% fat), while the trout they tested is a medium-fat fish (2–8% fat). The values come from different studies and methods, so they show a rough order rather than a direct comparison, and the chicken hearts and fish in the Semeniuc study were supermarket products that had passed their expiry date.

How much do people get from food?

Pravst and colleagues say the average dietary intake of CoQ10 is about 3 to 6 mg a day, with about half of it in the reduced form. A 1997 study by Weber and colleagues, based on Denmark's national dietary survey, estimated average intake in Denmark at 3–5 mg a day, about 64% of it from meat and poultry, with only minor contributions from cereals, fruit, edible fats and vegetables. No study estimating intake in Thailand was found.

Meat, fish, nuts and plant oils are all common in Thai cooking.

Is there a recommended daily amount?

CoQ10 is not among the nutrients in the Thai RDIs, so there is no Thai daily figure for it. Weber and colleagues (1997) also note that the optimal dietary intake of CoQ10 is unknown.

Does cooking reduce CoQ10?

Weber and colleagues (1997) analysed food in its edible form and found:

The limits: these figures come from Danish food in a single study, so Thai dishes with different ingredients and cooking methods may not give the same results.

Who should talk to a doctor or pharmacist before using CoQ10?

People taking regular medicines

NCCIH says CoQ10 may interact with some medicines, including medicines that make blood clot less easily, and that it may not be compatible with some types of medical treatment. If you take any regular medicine, or are under a doctor's ongoing care, ask your doctor or pharmacist first.

Pregnancy and breastfeeding

If you are pregnant, planning a pregnancy or breastfeeding, talk to a doctor before using CoQ10.

Mild effects that can occur

NCCIH says mild side effects such as digestive upsets may occur. Memorial Sloan Kettering lists infrequent effects such as nausea, diarrhoea and loss of appetite.

When to get advice

If you take a regular medicine, are under a doctor's ongoing care, or are pregnant or breastfeeding, talk to a doctor or pharmacist before using CoQ10.

Dietary supplements are not intended to prevent, treat or cure any disease.