PQQ (Pyrroloquinoline Quinone): Science-Based Guide to Benefits, Dosing, and Safety

PQQ (Pyrroloquinoline Quinone): Science-Based Guide to Benefits, Dosing, and Safety

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Pyrroloquinoline quinone (PQQ) is a redox-active, water-soluble quinone compound with the chemical structure 4,5-dihydro-4,5-dioxo-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid [1][2]. It is a reddish-brown antioxidant compound that functions primarily as a cofactor for bacterial dehydrogenases and exhibits potent antioxidant properties in mammalian systems [1][2]. PQQ was first discovered in the late 1960s as a novel cofactor in bacterial enzymes like glucose and alcohol dehydrogenases, with researchers Christopher Anthony and Leslie Zatman characterizing its unusual properties [2][14]. Its full chemical structure was elucidated in the 1970s, and the total chemical synthesis was achieved in 1981 by E. J. Corey and A. Tramontano through a 10-step route [2].

PQQ is classified as a vitamin-like accessory factor due to its involvement in essential biological processes such as mitochondrial biogenesis, growth, reproduction, and cellular energy production, though it is not officially recognized as a vitamin by major health authorities including the FDA and WHO as of 2025 [1][2]. The question of whether PQQ qualifies as the "14th vitamin" has been debated since the mid-1990s when studies by Robert B. Rucker's group demonstrated that PQQ-deficient diets impaired growth, reproduction, and immune responses in mice [2][3]. These mouse models showed reduced mitochondrial function and altered connective tissue integrity without PQQ. However, no PQQ-dependent enzyme has been identified in mammals, distinguishing its roles from prokaryotic systems, and the compound is considered an exogenous factor rather than a true vitamin [2].

Unlike vitamins that humans can synthesize to some degree, PQQ is not produced endogenously and must be obtained through dietary sources [1]. Despite marketing claims that may suggest otherwise, PQQ is not an essential nutrient and there is no established daily requirement for it [1]. It is present in extremely small amounts in plant-based foods — potatoes, green peppers, spinach, and green tea contain between 10 and 30 nanograms (0.000001 to 0.000003 mg) per gram [1][4]. This is vastly lower than the 10-20 mg doses used in clinical trials, which are produced industrially through chemical synthesis or bacterial fermentation [1]. Trace amounts of PQQ are also detected in mammalian tissues and fluids at low concentrations (e.g., 10-20 pg/g in human liver), likely derived from microbial or dietary intake rather than intestinal flora synthesis [2][13].

In biological systems, PQQ supports redox balance by directly scavenging reactive oxygen species (ROS), particularly superoxide radicals, with an IC50 value of approximately 1-6 x 10^-8 M [2]. It enhances NAD+-dependent sirtuin activity, promotes mitochondrial function and ATP synthesis via pathways including PGC-1alpha and CREB, influences lipid metabolism, reduces inflammation, and protects against oxidative stress-related conditions [2][5]. Laboratory studies have shown that PQQ stimulates the growth of new mitochondria (mitochondrial biogenesis), the production of nerve growth factor, and inhibits the growth of cancer cells and the synthesis of amyloid proteins associated with Alzheimer's disease [5][6][7].

Only a few small and relatively short human studies have investigated PQQ supplementation. Most have been placebo-controlled, and most have been funded at least in part by manufacturers of PQQ ingredients — particularly Mitsubishi Gas Chemical Company, Inc. (maker of BioPQQ) and Ryusendo Co. (maker of mnemoPQQ) [1]. This is important context for interpreting the evidence: the clinical data is limited in both quantity and independence.

Table of Contents

Overview

Pyrroloquinoline quinone (PQQ) is a redox-active, water-soluble quinone compound with the molecular formula C14H6N2O8 and a molecular weight of 330.21 g/mol [2]. It is an aromatic, tricyclic ortho-quinone characterized by a pyrrolo ring fused to a quinoline ring system, featuring three carboxylic acid moieties at positions 2, 7, and 9 — which contribute to its solubility and binding interactions — and an ortho-quinone functionality at positions 4 and 5 that enables redox cycling essential for its antioxidant role [2]. This redox cycling capacity — the ability to undergo repeated oxidation-reduction cycles — underlies its potent antioxidant activity.

PQQ was first reported in the 1960s as the prosthetic group of bacterial dehydrogenases. Researchers Christopher Anthony and Leslie J. Zatman purified the unknown cofactor and characterized its unusual properties [2][14]. In 1979, Salisbury and colleagues determined the structure via X-ray crystallography, revealing a tricyclic o-quinone scaffold. The total chemical synthesis was achieved in 1981 by E. J. Corey and A. Tramontano through a 10-step route [2]. In the early 1980s, the compound was formally named pyrroloquinoline quinone based on its pyrrole-quinoline core.

PQQ is classified as a vitamin-like accessory factor due to its involvement in mitochondrial biogenesis, growth, reproduction, and cellular energy production, though it is not officially recognized as a vitamin by the FDA or WHO as of 2025 [1][2]. The debate over whether PQQ qualifies as the "14th vitamin" began in the mid-1990s when Robert B. Rucker's group demonstrated that PQQ-deficient diets impaired growth, reproduction, and immune responses in mice [2][3]. These mouse models showed reduced mitochondrial function and altered connective tissue integrity. However, no PQQ-dependent enzyme has been identified in mammals, distinguishing PQQ's roles from prokaryotic systems where it acts as a redox cofactor in quinoprotein enzymes [2].

In mammals, PQQ is not produced endogenously and must be obtained through dietary sources. Typical dietary intake is estimated at 0.1-1.0 mg/day from foods [2], which is vastly lower than the 10-20 mg doses used in clinical trials. PQQ is found at trace levels in plant-based foods — potatoes, green peppers, spinach, and green tea contain between 10 and 30 nanograms per gram [1][4]. Trace amounts are also detected in mammalian tissues (e.g., 10-20 pg/g in human liver), likely derived from dietary intake rather than endogenous production [2][13].

PQQ's primary biological effects in mammals operate through non-cofactor signaling pathways. It supports redox balance by directly scavenging reactive oxygen species (particularly superoxide radicals), enhances NAD+-dependent sirtuin activity, promotes mitochondrial biogenesis via CREB phosphorylation and PGC-1alpha upregulation, influences lipid metabolism, and reduces inflammation [2][5]. Laboratory studies have demonstrated that PQQ stimulates the growth of new mitochondria, the production of nerve growth factor, inhibits cancer cell growth, and inhibits amyloid protein synthesis associated with Alzheimer's disease [5][6][7].

Forms and Bioavailability

PQQ Disodium Salt

All commercially available PQQ supplements contain PQQ as PQQ disodium salt [1]. This is the form used in clinical trials and the form filed as a new dietary ingredient (NDI) with the FDA. PQQ disodium salt has a molecular formula of C14H4N2Na2O8 and exhibits solubility of approximately 3 g/L at 25 degrees Celsius in water, while the free acid form has lower solubility and is not used in supplements [2][8].

Chemical Properties

PQQ demonstrates good stability in acidic conditions but is sensitive to alkali (decomposing at pH values above 8) and to light exposure under certain conditions [2][14]. It is thermally stable with a melting point exceeding 300 degrees Celsius [2][8]. The pKa values of its three carboxylic acid groups are approximately 1.2 (C7-COOH), 1.4 (C9-COOH), and 3.4 (C2-COOH) [2]. As a redox-active orthoquinone, PQQ undergoes a two-electron reduction to its quinol form (PQQH2), with a standard reduction potential of about +0.09 V vs. NHE at pH 7 [2][14]. In UV-Vis spectroscopy, PQQ displays characteristic absorption maxima at 248 nm and 400 nm in aqueous solution, attributable to pi-pi* transitions in its conjugated system [2][14]. The reduced quinol form exhibits fluorescence with an emission maximum around 450-500 nm, which can be used for analytical detection [2].

Branded Ingredients

Several branded PQQ ingredients are available on the market [1]:

  • BioPQQ — Manufactured by Mitsubishi Gas Chemical Company through bacterial fermentation. Mitsubishi was the first to introduce PQQ to the U.S. market in 2008 when it filed PQQ disodium salt as an NDI with the FDA and received no objection [1]. BioPQQ is the most commonly used ingredient in clinical trials and the most widely available branded form.
  • PureQQ — Manufactured by Nascent Health Sciences through chemical synthesis. In 2016, the FDA did not object to a GRAS notice for PureQQ in dietary supplements at a maximum of 8 mg per serving [1][8]. This is currently the only GRAS notice specifically covering dietary supplements.
  • mnemoPQQ — Manufactured by Ryusendo Co. Used in several recent Japanese clinical trials examining cognitive and physical performance benefits [9][10].
  • Other manufacturers — Additional GRAS notifications from Hisun (2016), Nutraland (2017), Fuzou Contay (2017), and JinCheng (2018) for bacterial fermentation PQQ at 5-20 mg per serving in drinks and beverages [1].

Fermentation vs. Chemical Synthesis

PQQ is produced commercially by two methods [1]:

Bacterial fermentation — Used by BioPQQ and several other manufacturers. PQQ is biosynthesized in certain prokaryotes (such as the methylotrophic bacterium Methylobacterium extorquens and Klebsiella pneumoniae) through a dedicated multi-enzymatic pathway encoded by the pqq operon, a gene cluster typically comprising pqqA through pqqE genes [2]. The pathway assembles PQQ from amino acid precursors — specifically L-glutamic acid (providing the pyrrole ring) and L-tyrosine (contributing the quinoline ring) [2]. The initial step involves a radical S-adenosylmethionine (SAM) enzyme PqqE catalyzing carbon-carbon bond formation between the glutamate and tyrosine residues, followed by proteolytic processing (PqqF/PqqG), hydroxylation (PqqB), and a final eight-electron, eight-proton oxidation by PqqC to yield PQQ [2].

Chemical synthesis — Used by PureQQ. The total chemical synthesis of PQQ was first achieved in 1981 by Corey and Tramontano through a 10-step route [2].

It is not clear if either production method yields a clinically superior product. In 2013, Mitsubishi Gas Chemical Company claimed that its own testing of competing PQQ products detected high levels of impurities, but these results do not appear to have been published in peer-reviewed literature [1].

Absorption and Pharmacokinetics

Upon ingestion, PQQ is rapidly absorbed in the small intestine with approximately 60% bioavailability in animal models [2][11]. Key pharmacokinetic parameters:

  • Peak serum concentrations: Reached within 2-3 hours after oral ingestion [2][11]
  • Distribution: PQQ distributes widely but accumulates preferentially in the kidney and skin, with up to 20% of the absorbed dose retained after 24 hours [2][11][12]
  • Excretion: Approximately 80% excreted unchanged in urine within 24 hours [2][11]
  • Plasma half-life: 3-5 hours in humans [2][11]
  • Water solubility: PQQ is water-soluble and does not require food for absorption [1]

The intestinal microbiota may contribute minimally to PQQ availability — diet remains the dominant source [2][11].

Evidence for Benefits

Memory and Cognition

Small, company-funded studies suggest PQQ may have a modest benefit on certain aspects of cognition among healthy adults, but PQQ does not appear to be helpful among people with mild cognitive impairment (MCI) [1].

Healthy adults with subjective forgetfulness (best available evidence): The most promising study involved 58 healthy adults in Japan ages 40 to under 80 who felt they had become more forgetful. About half the group received 21.5 mg daily of PQQ disodium salt (mnemoPQQ, by Ryusendo Co.) while the other half received placebo. After 12 weeks, the PQQ group had small improvements in 7 out of 11 aspects of cognitive function — including memory, attention, judgment, and cognitive flexibility — compared to placebo. However, the placebo group improved more than the PQQ group on complex attention, showing the effects were not uniformly positive. PQQ was taken as a capsule with water within 30 minutes after breakfast. Approximately 10% of participants reported stomach discomfort. The study was funded by Ryusendo Co. (Shiojima et al., J Am Coll Nutr, 2021) [9].

Middle-aged adults — PQQ alone and with CoQ10: A 2009 study reportedly found that 20 mg of PQQ taken daily for 12 weeks improved word recall and memory tasks in healthy, middle-aged adults compared to placebo, and that a daily dose of 20 mg PQQ plus 300 mg of CoQ10 resulted in greater cognitive improvements than PQQ alone. However, this study (published by Nakano in Food Style in 2009) does not appear to be available online, severely limiting the ability to evaluate its methodology and results [1].

Older adults — modest attention improvement: A trial among 41 older men and women (average age 58) reported a very modest improvement in certain measures of cognition such as attention with 20 mg of BioPQQ taken daily with breakfast for three months compared to placebo. However, this was only after the researchers excluded some participants' data from the study and performed a second analysis — the original primary analysis did not show significant benefit. The original, full study does not appear to be available, although some details have been published (Itoh et al., Adv Exp Med Biol, 2016) [15].

Elderly with mild cognitive impairment — no benefit: In a study among 34 older men and women (average age 72) with mild cognitive impairment (MCI), taking a tablet containing 20 mg of PQQ plus 80 mg of magnesium (Alpha Hope, by CalerieLife) twice daily for six weeks did not improve overall cognition based on the MMSE and ADAS-cog, except for a slight improvement in orientation — just one of 12 categories measured. One author is a CalerieLife employee (Baltic et al., J Nutr Health Aging, 2024) [16].

Ongoing clinical trials: As of 2025, clinical trials are evaluating PQQ's cognitive effects in specific populations, including postmenopausal women [2][35].

Preclinical neuroprotective evidence: Laboratory studies suggest PQQ inhibits the synthesis of amyloid proteins associated with Alzheimer's disease and enhances brain-derived neurotrophic factor (BDNF) expression, promoting synaptic plasticity and neuronal growth [2][7]. In models of Alzheimer's disease, PQQ reduces amyloid-beta toxicity by decreasing ROS production, preventing apoptosis, and restoring mitochondrial function in cultured neuronal cells [2]. For Parkinson's disease, PQQ protects dopaminergic neurons from rotenone-induced toxicity through activation of the PI3K/Akt signaling pathway [2]. Recent 2023 studies demonstrate PQQ's benefits in folate deficiency-induced neurodamage, restoring blood-brain barrier integrity in rodent models [2][17]. However, most neuroprotective evidence remains preclinical and has not translated to human cognitive benefits.

Synthesis: The cognitive evidence for PQQ in humans is weak. The best study showed only modest improvements in some cognitive domains, sample sizes are small (34-58 participants), study durations are short (6-12 weeks), and nearly all research is industry-funded. PQQ does not appear to help people with mild cognitive impairment. The strong preclinical evidence for neuroprotection has not convincingly translated into human cognitive benefits.

Energy, Mood, and Sleep Quality

One study found that 20 mg of PQQ daily for 8 weeks significantly improved measures of mood, fatigue, and sleep quality in adults ages 20 to 60 (Nakano et al., Functional Foods in Health and Disease, 2012) [18]. However, this study was not placebo-controlled, meaning it is impossible to distinguish genuine PQQ effects from placebo response, which is substantial for subjective outcomes like mood and fatigue. Without a placebo comparison, this study cannot establish causation.

The mechanistic rationale for energy enhancement is plausible: PQQ promotes mitochondrial biogenesis by activating key transcription factors including CREB and PGC-1alpha, leading to elevated mitochondrial DNA copy number and higher levels of respiratory chain proteins such as cytochrome c oxidase subunits [2][5][19]. In cell culture studies using mouse hepatocytes and myoblasts, PQQ treatment at concentrations of 10-30 micromolar for 24-48 hours significantly increased PGC-1alpha mRNA and protein expression through CREB phosphorylation at serine 133 [2][5]. PQQ also enhances energy production and lipid homeostasis by boosting ATP production in hepatocytes without changing basal respiration rates [2][26]. However, the leap from enhanced mitochondrial biogenesis in cell cultures to subjective energy improvements in humans has not been established in controlled trials.

Inflammation

A small study in 10 young adults (ages 21 to 34) found that approximately 20 mg of PQQ added to a fruit-flavored drink and taken for three days significantly reduced two markers of inflammation in the blood: C-reactive protein (CRP) and interleukin-6 (IL-6) (Harris et al., J Nutr Biochem, 2013) [20]. The study also observed alterations in urinary metabolites consistent with enhanced mitochondrial-related metabolism [20]. There was no placebo control and only 10 participants, making this extremely preliminary evidence.

At the cellular level, PQQ functions as a potent antioxidant through multiple mechanisms [2]:

  • Direct ROS scavenging: PQQ neutralizes superoxide and hydroxyl radicals, with an IC50 of approximately 1-6 x 10^-8 M in bacterial models of oxidative stress
  • Mitochondrial ROS reduction: PQQ inhibits ROS production in mitochondria, reducing oxidative stress associated with mitochondrial dysfunction
  • Antioxidant regeneration: PQQ supports the regeneration of other antioxidants, such as vitamins C and E, by facilitating their redox cycling and enhancing overall cellular defense against peroxidation
  • Nrf2 pathway activation: PQQ activates the Nrf2 pathway, which upregulates antioxidant gene expression and supports metabolic adaptation [2][21]

These mechanisms provide biological plausibility for anti-inflammatory effects, but the human evidence — a single uncontrolled study with 10 participants over 3 days — is insufficient to draw meaningful conclusions.

Muscle Strength, Exercise Endurance, and Body Composition

Older adults — modest strength improvements: A study in Japan among 62 healthy men and women (average age 54) found that taking 21.5 mg of PQQ disodium salt (mnemoPQQ, by Ryusendo Co.) daily for three months modestly increased leg extension strength compared to placebo. There were also slight improvements in hand grip strength and exercise tolerability (distance and speed during walking test, sit-to-stand test) compared to placebo. Notably, there were more adverse events in the PQQ group than placebo (23 vs 14 events), including headache, sore throat, fatigue, diarrhea, heartburn, and swollen gums. Funded by Ryusendo Co. (Shiojima et al., J Funct Foods, 2024) [10].

Young adults during exercise training — no benefit: A study among 23 healthy young men (average age 19) who participated in six weeks of endurance exercise training found that 20 mg of PQQ daily did not improve aerobic exercise performance or body composition compared to placebo. The PQQ was provided by Nascent Health Sciences, which funded the study and sells PQQ under the brand name PureQQ (Hwang et al., J Am Coll Nutr, 2019) [22].

Preclinical evidence on muscle aging: Animal studies show PQQ attenuates age-related muscle atrophy by improving mitochondrial biogenesis and reducing oxidative stress in aged mice [2][23]. Long-term PQQ supplementation has been shown to reprogram the single-cell landscape in aging tissues, lowering inflammatory markers and extending physiological healthspan in rodent models [2][24]. These animal findings have not been confirmed in human trials.

Ongoing clinical trials: As of 2025, clinical trials are evaluating PQQ's effects on exercise adaptation in non-trained individuals [2][36].

Synthesis: PQQ showed modest strength improvements in older sedentary adults but no benefit in young exercising adults. The evidence is too limited and inconsistent to recommend PQQ for exercise performance or body composition improvement. The age-related muscle preservation findings from animal studies are intriguing but unproven in humans.

Cholesterol-Lowering

One study suggests that PQQ may have a modest cholesterol-lowering effect. The study, conducted in Japan among 29 men and women (average age 49), found that 10 mg of BioPQQ taken twice daily (20 mg total) for three months lowered LDL ("bad") cholesterol compared to placebo — a decrease of 9 mg/dL with BioPQQ versus an increase of 3.7 mg/dL with placebo (Nakano et al., J Nutr Sci Vitaminol, 2015) [25].

This effect is comparable to what has been shown with CoQ10, another quinone compound involved in mitochondrial function [1]. However, the finding has important limitations:

  • Only 29 participants
  • Single study, not replicated
  • The muscle strength study by Shiojima et al. (2024) using a similar dosage of a different branded PQQ product (mnemoPQQ) did not replicate this cholesterol-lowering finding [10]

A 12-week study in adults with elevated triglycerides showed LDL reductions among those with baseline levels at or above 140 mg/dL [2], suggesting the effect may be limited to those with already-elevated cholesterol. Broader evidence remains preliminary and the clinical significance of a 9 mg/dL LDL reduction is modest compared to established cholesterol-lowering interventions.

Metabolic and Insulin-Sensitizing Effects

Animal studies demonstrate significant metabolic effects of PQQ supplementation [2][26][27]:

  • Diet-induced obesity models: PQQ improved insulin sensitivity and reduced hepatic fat accumulation by suppressing lipogenesis and promoting fatty acid beta-oxidation, while also boosting ATP production in hepatocytes without changing basal respiration rates [2][26][27]
  • High-fat diet-fed mice and rats: Doses of 0.2-2 mg/kg diet for 6-16 weeks decreased body weight gain, visceral fat mass, and fasting blood glucose levels [2][3][26]
  • Developmental programming: Early PQQ supplementation has persistent long-term protective effects on hepatic lipotoxicity and inflammation in obese mice [30]

Recent 2023-2024 investigations highlight PQQ's potential to mitigate insulin resistance and support metabolic health through improved mitochondrial function [2][26]. The mechanisms underlying these effects involve activation of the Nrf2 pathway and upregulation of antioxidant gene expression, as well as direct effects on lipid metabolism and glucose homeostasis through PGC-1alpha signaling [2][21].

Clinical trials as of 2025 are evaluating PQQ for metabolic disorders, including its effects on fat accumulation in obese women [2][28]. However, no published human clinical trial has demonstrated that PQQ supplementation improves insulin sensitivity, blood glucose, or body weight in people. The animal evidence is promising but the translation to humans remains to be proven.

Liver Protection (Preclinical Only)

In several animal studies, PQQ demonstrated hepatoprotective effects:

  • Liver injury: PQQ played a protective role against liver injury in mouse models (Huang et al., Exp Ther Med, 2015) [29]
  • High-fat diet liver damage: Early PQQ supplementation had persistent long-term protective effects on developmental programming of hepatic lipotoxicity and inflammation in obese mice (Jonscher et al., FASEB J, 2017) [30]
  • Liver disease progression: PQQ showed protective effects against non-alcoholic fatty liver disease (NAFLD) progression in animal models (Friedman et al., Hepatol Commun, 2018) [31]

However, there are no studies investigating PQQ's effects on liver disease in people [1]. The animal evidence is consistent but the lack of human data means PQQ cannot be recommended for liver protection.

Statin-Related Side Effects

While there is evidence that CoQ10 may help reduce statin-related side effects (muscle pain, weakness, etc.), there do not appear to be any studies on PQQ supplementation for statin-related side effects [1]. Given PQQ's structural and functional similarities to CoQ10 as a mitochondrial support compound, this would be a logical area for investigation, but no data exist.

Neuroprotection and Stroke (Preclinical Only)

In vivo evidence from rodent models of stroke shows that PQQ administration at 10 mg/kg intravenously reduces cerebral infarct size by approximately 40% in reversible middle cerebral artery occlusion, preserving neurological function 72 hours post-ischemia (Zhang et al., Exp Neurol, 2006) [32]. Similar neuroprotective effects occur in models of traumatic brain injury, where PQQ limits infarct expansion and oxidative damage [2].

At the cellular level, PQQ prevents apoptosis in neuronal cells by suppressing caspase activation and ROS-mediated pathways in response to glutamate or 6-hydroxydopamine toxicity [2]. It also enhances brain-derived neurotrophic factor (BDNF) expression, promoting synaptic plasticity and neuronal growth in models of neuroinflammation and aging [2].

These findings are exclusively preclinical — no human trials have evaluated PQQ for stroke prevention, stroke recovery, or traumatic brain injury.

Mitochondrial Biogenesis

PQQ's most well-characterized mechanism of action is the stimulation of mitochondrial biogenesis — the growth and division of new mitochondria within cells [5][2]. This is arguably the primary rationale for PQQ supplementation.

The seminal study by Chowanadisai et al. (J Biol Chem, 2010) demonstrated that PQQ stimulates mitochondrial biogenesis through a defined signaling cascade [5]:

  • PQQ activates CREB by phosphorylation at serine 133
  • Phosphorylated CREB upregulates PGC-1alpha gene expression
  • PGC-1alpha activates nuclear respiratory factors (NRF-1 and NRF-2)
  • This leads to increased mitochondrial DNA copy number and elevated levels of respiratory chain proteins such as cytochrome c oxidase subunits [2][5][19]

Animal deficiency studies confirm PQQ's importance: mice fed PQQ-deprived diets (<0.3 ng/g) show reduced mitochondrial content, reduced fertility (fewer pups per litter and lower conception rates), impaired immune responses (decreased T-cell proliferation), and growth retardation — all of which are ameliorated by supplementation at 0.3-2 micrograms/g diet [2][3][19][33]. The effects are dose-dependent, with mitochondrial content increasing proportionally with PQQ supplementation [2][3].

Importantly, PQQ does not directly participate in the mammalian electron transport chain as it does in bacterial systems. In bacteria, PQQ serves as a non-covalently bound redox cofactor in quinoprotein enzymes like glucose dehydrogenase and methanol dehydrogenase, facilitating substrate oxidations in energy metabolism [2]. No PQQ-dependent enzymes have been identified in mammals [2]. Instead, PQQ exerts non-cofactor effects through CREB/PGC-1alpha activation and Nrf2 pathway modulation [2][21].

Subsequent work by Saihara et al. (Biochemistry, 2017) confirmed that PQQ stimulates mitochondrial biogenesis by activating the SIRT1/PGC-1alpha signaling pathway, providing an additional mechanism beyond direct CREB phosphorylation [21].

Potential Synergy with CoQ10 and NAD+ Precursors

The 2009 Nakano study suggested that 20 mg PQQ plus 300 mg CoQ10 produced greater cognitive improvements than PQQ alone [1]. Since both compounds support mitochondrial function through different mechanisms — PQQ stimulates biogenesis of new mitochondria while CoQ10 supports electron transport within existing mitochondria — a synergistic effect is biologically plausible but unconfirmed in well-designed, available trials.

PQQ may also offer synergistic benefits when combined with nicotinamide mononucleotide (NMN), an NAD+ precursor [2]. The rationale is that PQQ and NMN target complementary aspects of mitochondrial health:

  • PQQ: Stimulates mitochondrial biogenesis through PGC-1alpha/CREB pathways and provides antioxidant protection
  • NMN: Elevates NAD+ levels to support sirtuin activity and cellular energy production
  • Convergence point: Both pathways converge on SIRT1/PGC-1alpha signaling, potentially enhancing each other's effects

Available data indicate no known adverse interactions between PQQ and NAD+ precursors [2]. Such combinations are used in supplement formulations without documented safety concerns, though comprehensive human trials examining combined PQQ-NMN or PQQ-CoQ10 safety and efficacy have not been conducted. The purported synergies remain theoretical.

Animal Deficiency Evidence

Studies in mice fed PQQ-deprived diets have been instrumental in understanding PQQ's biological importance [2][3][33]:

  • Growth: PQQ deprivation causes growth retardation that is reversed upon supplementation
  • Reproduction: Reduced fertility (fewer pups per litter, lower conception rates)
  • Immune function: Decreased T-cell proliferation and impaired immune responses
  • Skin and connective tissue: Altered connective tissue integrity (friable skin)
  • Mitochondrial function: Reduced mitochondrial content, lower respiratory chain protein expression, reduced mitochondrial DNA copy number

These deficiency effects occur at dietary PQQ levels below 0.3 ng/g and are dose-dependently reversed by supplementation at 0.3-2 micrograms/g diet (approximately equivalent to 1 micromole/kg diet in mice) [2][3]. While these findings strongly support PQQ's physiological importance, the absence of a confirmed mammalian apo-enzyme form means PQQ does not meet the classical definition of a vitamin [2].

Clinical Trial Doses

The typical dose of PQQ used in clinical studies is 20 mg per day, taken either as 10 mg twice daily or 20 mg once daily [1]. One research group used 21.5 mg per day [9][10]. The range across published studies is 10-21.5 mg per day, with one study using 40 mg per day (20 mg twice daily) [16].

Study Daily Dose Duration Form Outcome
Shiojima et al., 2021 (cognition) [9] 21.5 mg 12 weeks mnemoPQQ capsule Modest cognitive improvements
Shiojima et al., 2024 (muscle) [10] 21.5 mg 12 weeks mnemoPQQ capsule Modest strength improvement
Nakano et al., 2012 (mood/sleep) [18] 20 mg 8 weeks BioPQQ Improved mood/sleep (no placebo)
Nakano et al., 2015 (cholesterol) [25] 20 mg (10 mg x2) 12 weeks BioPQQ LDL reduction (-9 mg/dL)
Itoh et al., 2016 (cognition) [15] 20 mg 12 weeks BioPQQ Modest attention improvement
Hwang et al., 2019 (exercise) [22] 20 mg 6 weeks PureQQ No benefit
Harris et al., 2013 (inflammation) [20] ~20 mg 3 days PQQ in drink Reduced CRP and IL-6
Baltic et al., 2024 (MCI) [16] 40 mg (20 mg x2) 6 weeks Alpha Hope tablet No benefit in MCI
Nakano, 2009 (cognition) [1] 20 mg 12 weeks Not specified Improved recall (unavailable online)

How to Take

Suggested usage instructions on supplement labels are conflicting — some brands suggest taking PQQ with water while others suggest taking it with food [1]. Key considerations:

  • Absorption: PQQ is water-soluble and does not require food for absorption [1]
  • GI tolerance: Approximately 10% of PQQ users reported stomach discomfort [9], so taking with food may help
  • Timing in trials: PQQ was typically taken within 30 minutes after breakfast [9][10], or split into two daily doses taken before breakfast and dinner [16]
  • Peak levels: PQQ reaches peak serum concentrations within 2-3 hours after ingestion [2][11]
  • Half-life: Plasma half-life is 3-5 hours [2][11], suggesting twice-daily dosing may maintain more consistent blood levels than once-daily dosing

GRAS Status and Regulatory Position

Multiple GRAS notifications have been filed with the FDA [1][8]:

  • Mitsubishi Gas Chemical (BioPQQ), 2008: Filed PQQ disodium salt as an NDI. FDA did not object.
  • Nascent Health Sciences (PureQQ), 2016: FDA did not object to GRAS for dietary supplements at a maximum of 8 mg per serving. Currently the only GRAS notice specifically covering dietary supplements [1][8].
  • Hisun (2016), Nutraland (2017), Fuzou Contay (2017), JinCheng (2018): GRAS for fermented PQQ at 5-20 mg per serving in drinks and beverages [1].

GRAS status is based on filings to which the FDA has not objected but does not represent formal FDA confirmation of safety [1]. The FDA has indicated that PQQ disodium salt is safe for use at levels up to 0.1 mg/kg body weight per day (approximately 7 mg/day for a 70 kg adult) based on the initial GRAS filing, and up to 0.3 mg/kg body weight daily (approximately 21 mg/day for a 70 kg adult) based on subsequent notifications [2][8].

Practical Dosing Summary

  • General supplementation: 10-20 mg per day, the range used in most clinical trials
  • No established RDA: PQQ is not an essential nutrient and has no recommended dietary allowance or daily value
  • No UL established: Unlike many vitamins and minerals, there is no tolerable upper intake level for PQQ
  • Timing: Can be taken with or without food; taking with breakfast may reduce GI side effects
  • Duration: Clinical trials lasted 3 days to 12 weeks; long-term safety data beyond 3 months is not available
  • Typical dietary intake: 0.1-1.0 mg/day from food sources [2] — supplemental doses are 10-200x higher than dietary intake

Safety and Side Effects

Reported Adverse Effects

Mild adverse effects have been reported with PQQ supplementation in clinical trials. The most comprehensive safety data comes from the Shiojima et al. (2024) muscle strength study, which systematically tracked adverse events [1][10]:

  • Headache
  • Dizziness
  • Nausea
  • Heartburn
  • Diarrhea
  • Sore throat
  • Fatigue
  • Swollen gums

In the Shiojima et al. (2024) study, there were notably more adverse events in the PQQ group compared to placebo (23 vs 14 events) [10]. In the Shiojima et al. (2021) cognition study, approximately 10% of PQQ participants reported stomach discomfort [9]. These are generally mild and self-limiting adverse effects, but the higher rate in the PQQ group compared to placebo is noteworthy.

Severe Adverse Effects

Severe adverse effects have not been reported in clinical trials [1]. However, only short-term studies have been conducted — lasting several weeks to three months — typically at about 20 mg per day [1]. The absence of severe adverse effects in a small number of short trials does not establish long-term safety.

Long-Term Safety

The safety of PQQ supplementation at higher dosages or long-term has not been evaluated in clinical trials [1]. All published human data comes from studies lasting 3 days to 12 weeks. There are no data on PQQ safety when taken for months or years at supplemental doses.

Toxicology and Genotoxicity Data

PQQ is classified as non-toxic at dietary levels [2]:

  • No significant genotoxicity observed in vivo [2]
  • No significant adverse effects in animal studies at normal supplementation levels [2]
  • Animal deficiency studies demonstrate that PQQ deprivation (dietary levels <0.3 ng/g) causes reversible harm including reduced fertility, impaired immune responses, and growth retardation, suggesting the compound plays important physiological roles [2][3][33]
  • PQQ is naturally present in human breast milk at approximately 20-30 micrograms per liter [2][3], indicating it is a normal component of human nutrition at trace levels

Special Populations

Pregnancy and lactation: No data are available on PQQ supplementation during pregnancy or lactation. PQQ is naturally present in breast milk [2][3], but this does not establish the safety of supplemental doses (10,000-20,000 micrograms per day) during pregnancy or lactation.

Children: No data exist on PQQ supplementation in children or adolescents.

Kidney disease: Given that approximately 80% of PQQ is excreted unchanged in urine [2][11], impaired kidney function could theoretically lead to PQQ accumulation. No studies have evaluated PQQ in patients with renal impairment.

Cancer patients: Laboratory studies show PQQ inhibits the growth of cancer cells [6] and induces apoptosis via mitochondrial-dependent pathways. Whether this translates to clinically meaningful effects or potential interference with cancer treatments in humans is unknown.

Drug Interactions

There are no well-documented drug interactions with PQQ in the published literature. The limited number of human studies (fewer than 10 published trials) and short durations (3 days to 12 weeks) mean that meaningful interactions may not yet have been identified.

Theoretical Considerations

Anticoagulants and antiplatelet agents: PQQ has antioxidant effects and may influence inflammatory pathways including CRP and IL-6 [20]. No interaction has been documented, but individuals on blood thinners (warfarin, heparin, direct oral anticoagulants) should exercise caution with any new supplement and consult their healthcare provider.

Chemotherapy agents: Laboratory studies show PQQ inhibits the growth of cancer cells and induces apoptosis through mitochondrial-dependent pathways [6]. Whether supplemental PQQ could interfere with or enhance chemotherapy drugs is unknown. Patients undergoing cancer treatment should consult their oncologist before taking PQQ.

Cholesterol-lowering medications: PQQ may modestly lower LDL cholesterol based on one study (approximately 9 mg/dL reduction) [25], which could theoretically be additive with statin effects. No interaction studies have been conducted.

CoQ10 and NAD+ precursors: One study suggested enhanced cognitive benefits when PQQ was combined with CoQ10 [1]. There are no reports of adverse interactions between PQQ and CoQ10 or NMN/NR supplements [2]. These combinations are used in supplement formulations without documented safety concerns, though formal interaction studies have not been performed.

Medications metabolized by cytochrome P450 enzymes: PQQ's redox activity could theoretically affect drug metabolism through CYP450 enzyme modulation, but no studies have investigated this possibility.

Immunosuppressive medications: PQQ may modulate immune function based on animal studies showing that PQQ deficiency impairs T-cell proliferation [2][3]. Whether supplemental PQQ could enhance immune responses enough to interfere with immunosuppressive therapy is unknown but theoretically possible.

The standard recommendation is to inform your healthcare provider about PQQ supplementation, particularly if taking prescription medications, and to separate PQQ from medications by at least 2 hours as a general precaution.

Dietary Sources

PQQ is found in extremely small amounts in various foods. The concentrations are orders of magnitude lower than supplemental doses — food sources are measured in nanograms per gram (billionths of a gram), while supplement doses are in milligrams (thousandths of a gram), approximately a 1,000-fold difference [1][2][4].

Food PQQ Content (ng/g) Notes
Natto (fermented soybeans) Up to 61 Highest known food source; fermentation by PQQ-producing bacteria [2][13]
Parsley 34 Fresh parsley [2][13]
Kiwi fruit 27 [2][13]
Papaya 27 [2][13]
Tofu 24 [4]
Green tea 10-30 Brewed [1][4]
Green peppers 10-30 [1][4]
Spinach 10-30 [1][4]
Potatoes 10-30 [1][4]
Cocoa 3.7-30 Range depends on processing [2][13]
Celery 6 [4]

Source: Kumazawa et al., Biochem J, 1995 [4]; additional analyses [2][13].

The typical dietary intake of PQQ is estimated at 0.1-1.0 mg per day from foods [2]. To put this in perspective:

  • A clinical trial dose of 20 mg would require consuming roughly 330 kg of natto (the highest food source) per day
  • More than 660 kg of green peppers would be needed to match a 20 mg supplement dose
  • Food sources provide PQQ as part of a complex food matrix and may have different bioavailability than supplemental PQQ disodium salt
  • Human breast milk contains approximately 20-30 micrograms per liter of PQQ [2][3], substantially higher than concentrations in most foods but still far below supplemental doses (10,000-20,000 micrograms per day)

PQQ is produced exclusively by certain prokaryotes (bacteria), not by plants, animals, or fungi [2]. It enters the food chain through the following pathway: soil bacteria and rhizobacteria synthesize PQQ via the pqq operon biosynthetic pathway [2]; PQQ-producing bacteria in the rhizosphere promote plant growth by enhancing nutrient uptake and providing immunity against pathogens [2][34]; plants take up trace amounts of PQQ from the soil; fermented foods like natto have higher PQQ content because fermentation involves PQQ-producing bacteria [2][13].

In agricultural contexts, PQQ-producing bacteria such as Pseudomonas fluorescens B16 stimulate seed germination, pollen development, and root elongation, functioning as a plant growth promotion factor [2][34]. This bacterial production of PQQ represents the primary origin of all PQQ in the human food supply. While the intestinal microbiota could theoretically contribute to PQQ availability, studies indicate that gut bacteria produce little if any detectable PQQ [2][11]. Diet — particularly fermented foods, green vegetables, and tea — remains the dominant source of PQQ for humans.

References

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