Creatine is a an amino acid that your body naturally creates in your pancreas, liver and kidneys. It is also available in supplements and food sources such as fish, lean red meat and wild game. In some cases, use of creatine supplements may alter the effects of insulin, a hormone your body uses to control glucose levels in your bloodstream.
After creatine is created internally, your body stores it in your muscles in a chemical form called phosphocreatine or creatine phosphate. When you participate in short-duration, high-exertion exercises such as sprinting or weightlifting, your body draws on stored reserves of phosphocreatine to create a major source of cellular energy called adenosine triphosphate, or ATP. Proponents of creatine supplementation often recommend taking creatine-containing products as a way to improve athletic performances and promote the formation of lean muscle mass. However, the effects of supplementation vary greatly from person to person.
Insulin and Glucose
Your body produces insulin inside specialized cells located in your pancreas. When you eat, the carbohydrates in your food are converted into a simple form of sugar called glucose; this glucose then enters your bloodstream, where it acts as an energy source for a wide variety of cells. However, without certain signals from circulating insulin, your cells won’t let glucose pass into their interiors. If this occurs, your cells will starve and glucose will build up abnormally in your bloodstream. Individuals who don’t produce sufficient amounts of insulin or can’t properly use their insulin supplies develop the common medical condition called diabetes.
Use of creatine supplements can trigger changes in your blood glucose by changing your body’s responses to insulin in your bloodstream, lowering your blood sugar levels, according to the May 2011 "Medicine and Science in Sports and Exercise." Because of this effect you should use caution when taking creatine if you have diabetes or a low blood glucose disorder called hypoglycemia. Caution is also recommended if you also take other medications, supplements or herbs known to alter glucose levels.
Additional potential side effects of creatine supplementation include nausea, appetite loss, diarrhea, stomach upset, fever, reduced blood volume, dehydration and weight gain. Use of creatine may also cause damage to your kidneys or liver, and MedlinePlus.com advises avoidance of creatine-containing products if you are taking medications that affect the kidneys. Additionally, avoid using creatine if you are pregnant or nursing. Do not give creatine to a child or teenager. Medications that may interact adversely with creatine include diuretics, nonsteroidal anti-inflammatories and the gout medication probenicid.
Most suitable adults can use creatine for as long as six months without experiencing significant side effects, the University of Maryland Medical Center notes. Still, if you take a creatine-containing product, tell your doctor and ask him to monitor the product’s effects on your system. Pasteurized cow’s milk may contain more creatine than breast milk. However, doctors don’t know if this increased creatine level presents any significant health concerns.