Niacin plays an essential role in the activities of enzymes involved in carbohydrate and fat metabolism, nervous and digestive system functioning, manufacture of sex hormones, and maintenance of healthy skin. The coenzyme forms of niacin (NAD and NADH) are electron carriers and play an important role in glycolysis and the Krebs cycle, two important energy-producing cycles in the body. Inositol hexanicotinate functions as niacin without the characteristic "flush."