Creatine is a nitrogen-containing compound made from three amino acids; arginine, glycine, and methionine. Both humans and animals have the capacity to store creatine in their muscle tissue so creatine can be obtained through the diet by eating meat, fish, and poultry. Creatine can also be synthesized in the liver and kidneys if adequate amounts of the necessary amino acids are available.
Figure 8.6 Chemical Structure of Creatine
After it has been synthesized or absorbed, creatine is transported in the blood to the tissues. The majority of creatine is stored in skeletal muscle where creatine can be phosphorylated to become creatine phosphate (CP). About two-thirds of intramuscular creatine is stored as CP and the remaining creatine is stored as free creatine (1). Each day, between 1-3 g of creatine is converted into the metabolic byproduct creatinine and excreted in the urine. This means that the body needs to consume and/or synthesize 1-3 grams of creatine each day (1). Depending on the degree to which animal products are eliminated from the diet, a vegetarian’s intake of creatine may be low or nonexistent. Vegetarians can still synthesize creatine if they have adequate amounts of the necessary amino acids. However, research has suggested that vegetarians have lower creatine stores than non-vegetarians (2). They are not deficient in creatine, they are just on the low-normal end of the range.
Creatine is one of the most heavily researched nutritional supplements for athletes and has consistently been shown to be safe and effective for enhancing high-intensity exercise capacity and body composition in adults of all ages and even children (3). Emerging research suggests that creatine may also provide therapeutic benefits to certain populations throughout the lifespan (4). An average diet containing 1-2 grams of creatine per day leaves muscle creatine stores 60-80% saturated and these numbers are likely lower for vegetarians (1). The goal of creatine supplementation for athletes is to increase muscle creatine stores. There are several different forms of creatine, but the most common and cost effective form of creatine is creatine monohydrate.
There are two phases to the traditional creatine supplementation protocol, a loading phase and a maintenance phase. During the loading phase, an individual will ingest 5g of supplemental creatine 4 times a day. The goal of the loading phase is to saturate the muscle creatine stores as quickly as possible. Once muscle creatine stores are saturated, creatine stores can be maintained through a single dose of 5g of supplemental creatine per day. However, this loading and maintenance strategy is not needed unless an athlete is trying to maximize muscle creatine stores as quickly as possible. If time is not an issue, an individual can simply supplement with 3-5g of creatine per day for 4 weeks to obtain the same benefits (3). Combining creatine with carbohydrate or protein has been shown to increase creatine uptake and retention (1). However, athletes can still gain benefits from creatine even when not consumed with carbohydrate or protein. The most important thing is to take the supplement consistently. After the cessation of creatine supplementation, muscle creatine levels will drop back to baseline within 6-8 weeks (1).
Creatine and Performance
Not all athletes respond to creatine supplementation to the same degree. Some athletes respond to supplementation with substantial increases; however, some athletes are low responders and some are nonresponders. This is most likely due to the degree of muscle saturation with creatine prior to supplementation. Individuals with lower baseline muscle creatine stores will likely see more benefits from supplementation. Supplementation in vegetarians has been shown to increase muscle creatine levels more than in omnivores (2). Research has also shown that women have approximately 70-80% lower baseline muscle creatine stores than men which suggests that women may benefit from creatine supplementation more than men (5).
The majority of research on the performance benefits of creatine supplementation have documented both ergogenic and performance benefits for strength, speed, and power athletes. However, the improvement is not immediate. A good analogy for creatine supplementation is to consider the difference in driving distance when your car’s gas tank is totally full of gas rather than partially full. Supplementing allows the athlete to maximize creatine storage in the muscle. If the muscles are completely saturated, the athlete can “go farther,” or do more work. The larger volume of training allows the athlete to make greater gains in strength, speed, and power down the road.
Research has also consistently shown that creatine supplementation is safe. When supplementation first became popular, there were concerns that it could cause side effects such as dehydration, muscle cramps, and kidney damage. There is no scientific evidence that creatine causes any of these side effects. Maintenance doses of creatine have been shown to be safe for individuals with kidney disease and type 2 diabetes (1). However, individuals with pre-existing kidney disease should consult a physician prior to taking high doses of creatine supplements. The only reported side effects of creatine supplementation are bloating, minor GI upset, and weight gain. The bloating and weight gain is likely due to the extra creatine and water stored in the muscles. Most GI problems are alleviated by increasing fluid intake and/or reducing the maintenance dosage.
Other Functions of Creatine
In addition to the well established performance benefits of creatine, there is also emerging evidence that creatine may play a role in reducing risk of several chronic diseases. Sarcopenia (loss of muscle mass due to aging) and osteoporosis (weakening of the bones) are common health problems among older adults. While both of these diseases are multifactorial, research has suggested that creatine supplementation in combination with resistance training may help older adults maintain their muscle mass while they age (4). This maintenance of muscle mass allows older adults to continue to engage in bone strengthening activities which may help maintain bone density and reduce rates of osteoporosis. Limited research suggests that creatine supplementation increases the sensitivity of GLUT-4 translocation to the cell membrane which may help reverse insulin resistance in combination with exercise (4). Creatine can also help maintain energy availability during a heart attack or stroke and limit damage related to ischemia and may help strengthen the heart muscle of patients who suffer from heart failure (6). However, creatine’s role in improving exercise capacity may be more beneficial for strengthening the heart in patients with heart failure.