Coenzyme Q10 (CoQ10) is a fat-soluble, vitamin-like substance in every human cell. It's involved in key biochemical reactions that produce energy in cells. It also acts as an antioxidant (an"tih-OK'sih-dant). CoQ10 is naturally present in a variety of foods. Organ meats such as heart, liver and kidney as well as in beef, soybean oil, sardines, mackerel and peanuts are particularly high in CoQ10.