Creatine is naturally synthesized in the human body from amino acids primarily in the kidney and liver and transported in the blood for use by muscles. Approximately 95% of the body's total creatine content is located in skeletal muscle. Creatine was discovered in the 1800s as an organic constituent of meat. In the 1970s, Soviet scientists reported that oral creatine supplements may improve athletic performance during brief, intense activities such as sprints. Creatine gained popularity in the 1990s as a "natural" way to enhance athletic performance and build lean body mass. It was reported that skeletal muscle total creatine content increases with oral creatine supplementation, although response is variable. Factors that may account for this variation are carbohydrate intake, physical activity, training status, and muscle fiber type. The finding that carbohydrates enhance muscle creatine uptake increased the market for creatine multi-ingredient sports drinks. Use of creatine is particularly popular among adolescent athletes, who are reported to take doses that are not consistent with scientific evidence, and to frequently exceed recommended loading and maintenance doses. Published reports suggest that approximately 25% of professional baseball players and up to 50% of professional football players consume creatine supplements. According to a survey of high school athletes, creatine use is common among football players, wrestlers, hockey players, gymnasts, and lacrosse players. In 1998, the creatine market in the United States was estimated at $200 million. In 2000, the National Collegiate Athletic Association (NCAA) banned colleges from distributing creatine to their players. Creatinine excreted in urine is derived from creatine stored in muscle.
Coenzyme Q10 (CoQ10) is produced by the human body and is necessary for the basic functioning of cells. CoQ10 levels are reported to decrease with age and to be low in patients with some chronic diseases such as heart conditions, muscular dystrophies, Parkinson's disease, cancer, diabetes, and HIV/AIDS. Some prescription drugs may also lower CoQ10 levels. Levels of CoQ10 in the body can be increased by taking CoQ10 supplements, although it is not clear that replacing "low CoQ10" is beneficial. CoQ10 has been used, recommended, or studied for numerous conditions, but remains controversial as a treatment in many areas.
Selenium is a trace mineral found in soil, water, and some foods. It is an essential element in several metabolic pathways. Selenium deficiency can occur in areas where the soil content of selenium is low and it may affect thyroid function and cause conditions such as Keshan disease. Selenium deficiency is also commonly seen in patients on total parenteral nutrition (TPN) as their sole source of nutrition. Gastrointestinal disorders may decrease the absorption of selenium resulting in depletion or deficiency. Selenium may be destroyed when foods are refined or processed. Specific dietary sources of selenium include brewer's yeast, wheat germ, butter, garlic, grains, sunflower seeds, Brazil nuts, walnuts, raisins, liver, kidney, shellfish (lobster, oyster, shrimp, scallops), and fresh-water and salt-water fish (red snapper, salmon, swordfish, tuna, mackerel, halibut, flounder, herring, smelts). Selenium is also found in alfalfa, burdock root, catnip, fennel seed, ginseng, raspberry leaf, radish, horseradish, onion, chives, medicinal mushrooms (reishi, shiitake), and yarrow. The role of selenium in cancer prevention has been the subject of recent study and debate. Initial evidence from the Nutritional Prevention of Cancer (NPC) trial suggests that selenium supplementation reduces the risk of prostate cancer among men with normal baseline PSA (prostate specific antigen) levels and low selenium blood levels. However, in this study, selenium did not reduce the risk of lung, colorectal, or basal cell carcinoma of the skin and actually increased the risk of squamous cell skin carcinoma. The ongoing Selenium and Vitamin E Cancer Prevention Trial (SELECT) aims to definitively address the role of selenium in prostate cancer prevention.