First, from the animal studies, it is pretty clear that not much PQQ is needed for normal growth and development (in every animal that has been studied at least). For example, as little as 200 to 300 nanograms per gram of diet seem to support normal growth and development in mice, which is about half the requirement for folic acid in mice (400 to 500 nanograms per gram of diet). Of potential relevance, this is also near the same concentration of pyrroloquinoline quinone derivatives scientists have found in human milk when expressed on a milk solid basis. In adult humans, who consume the equivalent of 400 to 500 grams of solid food per day (2000 to 3000 calories), one might infer from what is in human milk that 0.1 to 0.15 milligrams of PQQ equivalents (per day) might sustain normal function. For perspective, the adult human recommended dietary allowance for folic acid is near this amount, less than half a milligram. For most animals that have nutritional requirements for given dietary growth factors and vitamin-like compounds, the requirements are remarkably similar when they are expressed relative to dietary energy needs (or the number of kilocalories actually utilized). If done in this fashion, it is possible to extrapolate a guess for suggested human pyrroloquinoline quinone intake from animal models.
Then why is the amount added to supplements often 10 milligrams of PQQ (or more) as the daily dose?
First, the 0.1 to 0.15 milligrams of PQQ per day amount (referenced above) is based on the lowest extrapolated amount needed to promote growth in young animals. These studies were using highly purified diets or the direct extrapolation from human milk to get pyrroloquinoline quinone. When a more complex diet is consumed, it is assumed a higher amount of PQQ is needed. For example, to get a measured response in adult animals fed a complex diet (such as a change in mitochondrial function) there is the need to feed 2000 to 3000 nanograms of PQQ per gram of food (in other words, 10 times more than the amounts mentioned above). Some possible reasons are that consuming a complex diet activates numerous xenobiotics and secondary metabolism pathways, which can cause PQQ to be catabolized at higher rates. Also, at the gut level, there is a greater competition for nutrient absorption. Playing on this assumption, the amount of PQQ needed would be on the order of 1 to 1.5 milligrams pyrroloquinoline quinone (methoxatin) per day, which most humans get based on typical diets. Moreover, it is a reasonable assumption based on what researchers currently know about assessing and addressing the limits for other vitamins and growth factors. For example, consider the following for ascorbic acid (vitamin C): Although 8 to 15 milligrams might protect against the overt signs of scurvy, the recommended dietary allowance currently stands at 75 to 90 milligram per day (for adults, excluding pregnant and lactating women) for optimal function, and an even higher dietary reference intake (DRI) is again in review. Over and above these government recommendations, many supplements contain even more than this amount (depending on the application).
A second problem with making a more precise estimate of need is the fact that PQQ is very reactive and forms complexes easily with proteins and amino acids. There is evidence, however, that some of these complexes can dissociate back to methoxatin (pyrroloquinoline quinone). The nature of the products, however, makes it difficult to obtain precise data for nutritional balance determinations. There simply isn’t enough data to make assumptions about the percentage of PQQ complexes that are absorbed in humans. In mice, some data from studies using isotopically labeled PQQ suggests absorption is on the order of 40 to 60 percent, but more research is clearly needed.
So why have nutraceutical companies chosen 10 to 20 milligrams of PQQ per day as a dose for humans instead of a lower amount?
First, frankly there is the lack of precise nutritional data to make a general assumption of need. Although arbitrary, taking 10 mg per day, you can assume an optimal dose is being delivered for normal applications. Also in several clinical presentations, a 10 milligram dose in young adults lowers plasma triglyceride levels in some individuals, improves indices important to inflammation, and acts as a potent antioxidant. Further, the equivalent dose in animals has consistently improved various mitochondrial functions. Although anecdotal at this point, 10 to 20 milligrams per day seems to improve exercise tolerance in humans as well. Because PQQ (pyrroloquinoline quinone | methoxatin) has been shown to be safe at this amount (10 to 20 milligrams per day), it is currently the amount you will find in most supplement formulas.