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Coenzyme Q10 is one of the most researched nutrients in reproductive health. It plays a central role in mitochondrial energy production and antioxidant defence, both of which are critical for egg and sperm quality. Learn more about the role of CoQ10 here.
CoQ10 is gaining increasing attention when it comes to fertility, and for good reason. Learn more about how CoQ10 can impact both male and female fertility here.
It exists in two forms: ubiquinone and ubiquinol. Discussion around which form is "better" has become increasingly polarised, but this risks oversimplifying a complex area of physiology.
Below, we address five common myths about the differences between ubiquinol and ubiquinone, and explain how we approach this choice in a fertility focused context.
The Truth: Ubiquinone and ubiquinol are closely related, but they are not identical in function.
Ubiquinone is the oxidised form of CoQ10. Ubiquinol is the reduced form and the form that acts directly as an antioxidant in cell membranes and mitochondria.1 In the body, these two forms exist as a redox pair and can be converted back and forth depending on physiological need.
Importantly, around 90 to 95 percent of circulating CoQ10 in the blood is present as ubiquinol.2 This reflects its central role in antioxidant protection and cellular energy systems.
Describing ubiquinol as the active form is therefore not only a marketing term, but a reflection of its biological role.
The Truth: This is a bit of an oversimplification. Conversion is dynamic.
It is often stated that the body produces ubiquinone first and then converts it to ubiquinol as required. In reality, CoQ10 synthesis and conversion are part of a continuous and dynamic process that involves multiple enzyme systems.3
Research shows that conversion efficiency can decline with age and may be reduced in states of increased oxidative stress.4 This does not mean conversion stops, but it does mean that reliance on optimal conversion is an assumption that may not hold true for everyone. At the same time, multiple trials using ubiquinone alone in adults of reproductive age show improved ovarian response and sperm parameters, indicating that conversion still occurs in many people.5
In fertility, where oxidative balance is particularly important, this distinction becomes more relevant.
The Truth: Not Consistently Supported By The Studies
Another common claim is that ubiquinol is unstable and simply oxidises back to ubiquinone before absorption, making the choice irrelevant.
However, pharmacokinetic studies do not consistently support this across models. Human and animal studies measuring plasma CoQ10 ratios show that ubiquinol remains largely in its reduced form after ingestion.6 If significant oxidation occurred in the digestive tract, a measurable drop in circulating ubiquinol ratios would be expected. This is not consistently observed.
In addition, multiple studies using identical capsule formulations have demonstrated higher and more consistent plasma CoQ10 levels following ubiquinol supplementation compared with ubiquinone.7,8
This suggests that, when properly formulated, ubiquinol is both stable and efficiently absorbed.
The Truth: This Is A Little Misleading
It is true that many early fertility studies used ubiquinone, and this evidence remains valuable. These studies established CoQ10 as an important nutrient for egg and sperm quality and for supporting assisted reproductive outcomes.9
However, more recent fertility focused research increasingly includes ubiquinol, particularly in studies examining ovarian ageing, IVF outcomes, male factor infertility and oxidative stress related reproductive challenges.
Narrative reviews and controlled trials using ubiquinol have reported improvements in markers such as oocyte yield, embryo quality and sperm parameters.10,11 While further large scale studies are still needed, the emerging evidence base reflects growing interest in the reduced form of CoQ10 in reproductive settings.
Most of the largest and longest fertility trials to date have used ubiquinone or unspecified CoQ10, so we still need head to head fertility studies before declaring one form superior. The picture is therefore not one sided. Both forms have evidence, but the context in which they are used matters.
The Truth: It's What's Appropriate Vs What's Expensive
Ubiquinol is more expensive to produce than ubiquinone. This is largely due to the additional steps required to stabilise the reduced form and protect it from oxidation during manufacturing and storage.
This does not mean ubiquinol is necessary for everyone, nor does higher cost automatically translate to better outcomes in all cases. However, the price difference is not purely a branding exercise.
The more meaningful question is not which form is cheaper, but which form is most appropriate for the individual and the physiological demands they are under.
At Zita West, our formulations are designed for people who are actively trying to conceive, preparing for IVF or navigating age related fertility challenges.
Fertility places exceptional demands on mitochondrial energy production and antioxidant protection. Egg and sperm cells are highly sensitive to oxidative stress, and even small imbalances can affect quality and developmental potential.
While both forms of CoQ10 can raise overall CoQ10 levels, ubiquinol is the form that is immediately available for antioxidant activity and predominates in circulation. In several human studies using identical capsule bases, ubiquinol has produced higher and more consistent plasma CoQ10 levels than ubiquinone, especially in people whose baseline levels were low.7,8
For this reason, we choose ubiquinol. Not because ubiquinone is ineffective, but because ubiquinol aligns more closely with a precautionary, clinically focused approach in a fertility setting.
The debate between ubiquinol and ubiquinone is often framed too simply. In reality, both forms have a role.
Ubiquinone can be appropriate for general health and for individuals with robust metabolic function. Ubiquinol may be more suitable in situations where oxidative stress is high, conversion capacity may be reduced, or biological demands are particularly intense, such as during fertility treatment.
What matters most is not choosing a form based on marketing or price alone, but selecting a well produced supplement that fits the individual, the context and the stage of the fertility journey. Whichever form you choose, consistent daily use and an evidence based dose matter more than fine tuning the redox chemistry.
Ubiquinone is the oxidised form of CoQ10, while ubiquinol is the reduced form. Both exist naturally in the body and can be converted back and forth. Ubiquinol is the form that acts directly as an antioxidant and makes up 90 to 95 percent of circulating CoQ10 in the blood.
Several human studies using identical formulations have shown that ubiquinol produces higher and more consistent plasma CoQ10 levels compared with ubiquinone. However, absorption also depends on formulation quality and whether the supplement is taken with food containing fat.
Conversion efficiency can decline with age and in states of increased oxidative stress, but it does not stop. Clinical studies show that adults of reproductive age can still convert ubiquinone effectively, though individual variation exists.
Both ubiquinone and ubiquinol have evidence supporting their use in fertility. Early fertility studies primarily used ubiquinone, while more recent research increasingly includes ubiquinol. The choice may depend on individual factors such as age, oxidative stress levels and conversion capacity.
Ubiquinol requires additional manufacturing steps to stabilise the reduced form and protect it from oxidation during production and storage. This increases production costs compared with ubiquinone.
Yes. Many fertility studies using ubiquinone have been conducted in adults over 30 with positive results. While conversion efficiency may decline with age, it does not mean ubiquinone is ineffective in this age group.
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