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Study raises concerns over CoQ10 for cognitive health

By Stephen Daniells , 09-Sep-2009
Last updated on 10-Sep-2009 at 17:50 GMT2009-09-10T17:50:52Z

Study raises concerns over CoQ10 for cognitive health

Coenzyme Q10 (CoQ10) may not benefit mental function, and at high doses equivalent to 1700 mg per day may even be damaging, say findings from a mouse study.

Scientists from the University of North Texas Health Science Center and the University of Southern California report that, contrary to previous reports on the anti-ageing properties of CoQ10, prolonged, high-dose CoQ10 may speed up the loss of cognitive function associated with ageing.

“We did not detect any deleterious consequences from prolonged intake of a lower dose of CoQ10 (estimated human equivalent of 500 mg/day),” lead researcher Michael Forster told NutraIngredients. “However, none of the anticipated beneficial effects were observed.”

Of mice and men

Responding to the study, Andrew Shao PhD, vice president, scientific and regulatory affairs, at the Council for Responsible Nutrition (CRN), a trade organization, told NutraIngredients that the study’s relevance to the average consumer is “questionable”.

“The fact is, no matter how rigorous the research, extrapolating from rodents to humans has inherent limitations and requires many assumptions,” said Dr Shao, who co-authored a risk assessment on CoQ10 in 2006, published in Regulatory Toxicology and Pharmacology.

“Even if doses exceeding 1500 or 3000 mg CoQ10 per day were to cause harm (which we have yet to see in humans), no one is advocating such doses be used to prevent cognitive decline or maintain cardiovascular health,” he said.

“The dose at which such adverse effects might occur in humans from CoQ10 has still not been established; this study does not change that,” said Dr Shao.


CoQ10 has properties similar to vitamins, but since it is naturally synthesized in the body it is not classed as such. With chemical structure 2,3-dimethoxy-5-methyl-6-decaprenyl-1,4-benzoquinone, it is also known as ubiquinone because of its 'ubiquitous' distribution throughout the human body.

The coenzyme is concentrated in the mitochondria - the 'power plants' of the cell - and plays a vital role in the production of chemical energy by participating in the production of adenosince triphosphate (ATP), the body's co-called 'energy currency'.

There is an ever-growing body of scientific data that shows substantial health benefits of CoQ10 supplementation for people suffering from angina, heart attack and hypertension. The nutrient is also recommended to people on statins to off-set the CoQ-depleting effects of the medication. Other studies have reported that CoQ10 may play a role in the prevention or benefit people already suffering from neurodegenerative diseases.

However, according to results of the new mouse study, high doses may not be beneficial, and may even be damaging.

Mouse data

Prof Forster and his co-workers fed mice a control diet, or the same diet supplemented with 0.68 mg/g (low dose) or 2.6 mg/g (high dose) CoQ10 from four months of age until 25 months.

By looking at levels of different CoQs in various parts of the brain, they noted that both CoQ9H2 and CoQ10H2 were increased in a segment of the brain called the cerebral cortex. No increases were observed in other regions of the brain, they said.

No improvements in age-related declines in muscle strength, balance, coordinated running, or learning/memory were observed in the low-dose group. On the other hand, the higher dose was associated with decreases in hearing and response to shock stimuli, as well as an impairment of the spatial learning and memory.

Neither CoQ10 diets affected the lifespan of the animals, added the researchers.

“These findings do not support the notion that CoQ10 is a fitness-enhancing or an ‘anti-ageing’ substance under normal physiological conditions,” wrote the researchers.

Human equivalents

The low and high-dose diets would be equivalent to human doses of about 500 and 1700 mg/d, respectively, said the researchers, after adjusting for body weight differences between humans and mice.

“It would be fair to comment that the upper safe limit of 1200 mg per day recommended by the Council for Responsible Nutrition (CRN) is lower than the estimated human equivalent (1700 mg/day) of the dose leading to cognitive impairment in our mouse studies,” Dr Forster told this website.

“On the other hand, these numbers are a bit too close for my taste; based on our results one might be hesitant to take CoQ10 at 1200 mg/day for any length of time,” he added.

The Texas and Californian-based researchers conclusion that 500 mg per day therefore represents the upper safe limit is at odds with conclusions drawn by the CRN in 2006, which proposed a safe upper limit of 1,200 mg per day (Regulatory Toxicology and Pharmacology, 2006, Vol. 45, pp. 282-288).

“Correction for body weight (as they have done in this paper) does not necessarily address all the issues with this kind of extrapolation,” Dr Shao told “For that reason, and because we felt there were ample human data available, our 2006 risk assessment did not consider animal data,” he said.

“This study adds little to the understanding of CoQ10 safety other than the fact that high doses can have adverse effects in mice. High doses of anything (eventually) can have adverse effects on any species,” said Dr Shao.

Source: Journal of Nutrition
Published online ahead of print, doi: 10.3945/jn.109.110437
“Prolonged Intake of Coenzyme Q10 Impairs Cognitive Functions in Mice”
Authors: N. Sumien, K.R. Heinrich, R.A. Shetty, R.S. Sohal, M.J. Forster

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