PQQ is present in a variety of foods such as parsley, green tea, and fermented soybeans. PQQ is also abundant in human breast milk. The estimated daily intake of PQQ from typical foods and beverages are 0.01–0.4 mg/day. PQQ is an anti-oxidant and promotes mitochondrial biogenesis. Reduced PQQ exhibits a high anti-oxidant capacity that is 7.5-fold greater than that of ascorbic acid.