Low levels of red blood cells in people with a long-term illness (anemia of chronic disease). Taking vitamin C supplements might help manage anemia in people undergoing dialysis. Irregular heartbeat (atrial fibrillation). Taking vitamin C for a few days before and after heart surgery helps prevent irregular heartbeat after heart surgery. Emptying the colon before a colonoscopy. Before a person undergoes a colonoscopy, the person must make sure that their colon is empty. This emptying is called bowel preparation. Some bowel preparation involves drinking 4 liters of medicated fluid. If vitamin C is included in the medicated fluid, the person only needs to drink 2 liters. This makes people more likely to follow through with the emptying procedure. Also fewer side effects occur. A specific medicated fluid containing vitamin C (MoviPrep, Salix Pharmaceuticals, Inc.) has been approved by the U.S. Food and Drug Administration (FDA) for bowel preparation. Common cold. There is some controversy about the effectiveness of vitamin C for treating the common cold. However, most research shows that taking 1-3 grams of vitamin C might shorten the course of the cold by 1 to 1.5 days. Taking vitamin C does not appear to prevent colds. Limb pain that usually occurs after an injury (complex regional pain syndrome). Taking vitamin C after surgery or injury to the arm or leg seems to prevent complex regional pain syndrome from developing. Skin redness caused by injury or irritation (erythema). Using a skin cream containing vitamin C might decrease skin redness following laser resurfacing for scar and wrinkle removal. Airway infections caused by exercise. Using vitamin C before heavy physical exercise, such as a marathon or army training, might prevent upper airway infections that can occur after heavy exercise. High cholesterol. Taking vitamin C might reduce low-density lipoprotein (LDL or "bad") cholesterol in people with high cholesterol. High blood pressure. Taking vitamin C along with medicine to lower blood pressure might help lower systolic blood pressure (the top number in a blood pressure reading) by a small amount. But it does not seem to lower diastolic pressure (the bottom number). Lead poisoning. Consuming vitamin C in the diet seems to lower blood levels of lead. Reduced benefit of nitrate therapy that happens when nitrates are used all day (nitrate tolerance). In some people who take medicines for chest pain, the body develops tolerance and the medicines stop working as well. Taking vitamin C seems to help these medicines, such as nitroglycerine, work for longer.