Health implications of creatine: can oral creatine supplementation protect against neurological and atherosclerotic disease?
Major achievements made over the last several years have highlighted the important roles of creatine and the creatine kinase reaction in health and disease. Inborn errors of metabolism have been identified in the three main steps involved in creatine metabolism: arginine:glycine amidinotransferase (AGAT), S-adenosyllmethionine:N-guanidinoacetate methyltransferase (GAMT) and the creatine transporter. All these diseases are characterized by a lack of creatine and phosphorylcreatine in the brain, and by (severe) mental retardation. Similarly, knockout mice lacking the brain cytosolic and mitochondrial isoenzymes of creatine kinase displayed a slightly increased creatine concentration, but no phosphorylcreatine in the brain. These mice revealed decreased weight gain and reduced life expectancy, disturbed fat metabolism, behavioral abnormalities and impaired learning capacity. Oral creatine supplementation improved the clinical symptoms in both AGAT and GAMT deficiency, but not in creatine transporter deficiency. In addition, creatine supplementation displayed neuroprotective effects in several animal models of neurological disease, such as Huntington’s disease, Parkinson’s disease or amyotrophic lateral sclerosis. All these findings pinpoint to a close correlation between the functional capacity of the creatine kinase/phosphorylcreatine/creatine system and proper brain function. They also offer a starting-point for novel means of delaying neurodegenerative disease, and/or for strengthening memory function and intellectual capabilities. Finally, creatine biosynthesis has been postulated as a major effector of homocysteine concentration in the plasma, which has been identified as an independent graded risk factor for atherosclerotic disease. By decreasing homocysteine production, oral creatine supplementation may, thus, also lower the risk for developing, e.g., coronary heart disease or cerebrovascular disease. Although compelling, these results require further confirmation in clinical studies in humans, together with a thorough evaluation of the safety of oral creatine supplementation.
Methylation demand and homocysteine metabolism: effects of dietary provision of creatine and guanidinoacetate.
S-adenosylmethionine, formed by the adenylation of methionine via S-adenosylmethionine synthase, is the methyl donor in virtually all known biological methylations. These methylation reactions produce a methylated substrate and S-adenosylhomocysteine, which is subsequently metabolized to homocysteine. The methylation of guanidinoacetate to form creatine consumes more methyl groups than all other methylation reactions combined. Therefore, we examined the effects of increased or decreased methyl demand by these physiological substrates on plasma homocysteine by feeding rats guanidinoacetate- or creatine-supplemented diets for two week. Plasma homocysteine was significantly increased (~50%) in rats maintained on guanidinoacetate-supplemented diets, whereas rats maintained on creatine-supplemented diets exhibited a significantly lower (~25%) plasma homocysteine level. Plasma creatine and muscle total creatine were significantly increased in rats fed the creatine-supplemented or guanidinoacetate-supplemented diets. The activity of kidney L-arginine:glycine amidinotransferase, the enzyme catalyzing the synthesis of guanidinoacetate, was significantly decreased in both supplementation groups. To examine the role of the liver in mediating these changes in plasma homocysteine, isolated rat hepatocytes were incubated with methionine in the presence and absence of guanidinoacetate and creatine, and homocysteine export was measured. Homocysteine export was significantly increased in the presence of guanidinoacetate. Creatine, however, was without effect. These results suggest that homocysteine metabolism is sensitive to methylation demand imposed by physiological substrates.
Am J Physiol Endocrinol Metab 2001 Nov;281(5):E1095-100
Use of P-31 magnetic resonance spectroscopy to detect metabolic abnormalities in muscles of patients with fibromyalgia.
OBJECTIVE: To investigate the metabolic and functional status of muscles of fibromyalgia (FM) patients, using P-31 magnetic resonance spectroscopy (MRS). METHODS: Twelve patients with FM and 11 healthy subjects were studied. Clinical status was assessed by questionnaire. Biochemical status of muscle was evaluated with P-31 MRS by determining concentrations of inorganic phosphate (Pi), phosphocreatine (PCr), ATP and phosphodiesters during rest and exercise. Functional status was evaluated from the PCr/Pi ratio, phosphorylation potential (PP) and total oxidative capacity (Vmax). RESULTS: Patients with FM reported greater difficulty in performing activities of daily living as well as increased pain, fatigue and weakness compared with controls. MRS measurements showed that patients had significantly lower than normal PCr and ATP levels (P < 0.004) and PCr/Pi ratios (P < 0.04) in the quadriceps muscles during rest. Values for PP and Vmax also were significantly reduced during rest and exercise. CONCLUSION: P-31 MRS provides objective evidence for metabolic abnormalities consistent with weakness and fatigue in patients with FM. Noninvasive P-31 MRS may be useful in assessing clinical status and evaluating the effectiveness of treatment regimens in FM.
Arthritis Rheum 1998 Mar;41(3):406-13.
Creatine supplementation and health variables: a retrospective study.
PURPOSE: Long-term safety of creatine supplementation has been questioned. This retrospective study was performed to examine markers related to health, the incidence of reported side effects and the perceived training benefits in athletes supplementing with creatine monohydrate. METHODS: Twenty-six athletes (18 M and 8 F, 24.7 +/- 9.2 y; 82.4 +/- 20.0 kg; 176.5 +/- 8.8 cm) from various sports were used as subjects. Blood was collected between 7:00 and 8:30 a.m. after a 12-hour fast. Standard clinical examination was performed for CBC and 27 blood chemistries. Testosterone, cortisol and growth hormone were analyzed using an ELISA. Subjects answered a questionnaire on dietary habits, creatine supplementation, medical history, training history and perceived effects of supplementation. Body mass was measured using a medical scale, body composition was estimated using skinfolds and resting heart rate and blood pressure were recorded. Subjects were grouped by supplementation length or no use: Gp1 (control) = no use (N = 7; 3 F, 4 M); Gp2 = 0.8-1.0 yr (N = 9; 2 F, 7 M); and Gp3 = 1(+) (N = 10; 3 F, 7 M). RESULTS: Creatine supplementation ranged from 0.8--four year. Mean loading dose for Gp2 and Gp3 was 13.7 +/- 10.0 and the maintenance dose was 9.7 +/- 5.7 g.d(-)1. Group differences were analyzed using one-way ANOVA. CONCLUSIONS: Expected gender differences were observed. Of the comparisons made among supplementation groups, only two differences for creatinine and total protein (P < 0.05) were noted. All group means fell within normal clinical ranges. There were no differences in the reported incidence of muscle injury, cramps or other side effects. These data suggest that long-term creatine supplementation does not result in adverse health effects.
Med Sci Sports Exerc 2001 Feb;33(2):183-8
Adverse effects of creatine supplementation: fact or fiction?
The consumption of oral creatine monohydrate has become increasingly common among professional and amateur athletes. Despite numerous publications on the ergogenic effects of this naturally occurring substance, there is little information on the possible adverse effects of this supplement. The objectives of this review are to identify the scientific facts and contrast them with reports in the news media, which have repeatedly emphasised the health risks of creatine supplementation and do not hesitate to draw broad conclusions from individual case reports. Exogenous creatine supplements are often consumed by athletes in amounts of up to 20 g/day for a few days, followed by one to 10 g/day for weeks, months and even years. Usually, consumers do not report any adverse effects, but body mass increases. There are few reports that creatine supplementation has protective effects in heart, muscle and neurological diseases. Gastrointestinal disturbances and muscle cramps have been reported occasionally in healthy individuals, but the effects are anecdotal. Liver and kidney dysfunction have also been suggested on the basis of small changes in markers of organ function and of occasional case reports, but well-controlled studies on the adverse effects of exogenous creatine supplementation are almost nonexistent. We have investigated liver changes during medium term (four weeks) creatine supplementation in young athletes. None showed any evidence of dysfunction on the basis of serum enzymes and urea production. Short term (five days), medium term (nine weeks) and long term (up to five years) oral creatine supplementation has been studied in small cohorts of athletes whose kidney function was monitored by clearance methods and urine protein excretion rate. We did not find any adverse effects on renal function. The present review is not intended to reach conclusions on the effect of creatine supplementation on sport performance, but we believe that there is no evidence for deleterious effects in healthy individuals. Nevertheless, idiosyncratic effects may occur when large amounts of an exogenous substance containing an amino group are consumed, with the consequent increased load on the liver and kidneys. Regular monitoring is compulsory to avoid any abnormal reactions during oral creatine supplementation.
Sports Med 2000 Sep;30(3):155-70.
American College of Sports Medicine roundtable. The physiological and health effects of oral creatine supplementation.
Creatine (Cr) supplementation has become a common practice among professional, elite, collegiate, amateur and recreational athletes with the expectation of enhancing exercise performance. Research indicates that Cr supplementation can increase muscle phosphocreatine (PCr) content, but not in all individuals. A high dose of 20 g x d(-1) that is common to many research studies is not necessary, as 3 g x d(-1) will achieve the same increase in PCr given time. Coincident ingestion of carbohydrate with Cr may increase muscle uptake; however, the procedure requires a large amount of carbohydrate. Exercise performance involving short periods of extremely powerful activity can be enhanced, especially during repeated bouts of activity. This is in keeping with the theoretical importance of an elevated PCr content in skeletal muscle. Cr supplementation does not increase maximal isometric strength, the rate of maximal force production, nor aerobic exercise performance. Most of the evidence has been obtained from healthy young adult male subjects with mixed athletic ability and training status. Less research information is available related to the alterations due to age and gender. Cr supplementation leads to weight gain within the first few days, likely due to water retention related to Cr uptake in the muscle. Cr supplementation is associated with an enhanced accrual of strength in strength-training programs, a response not independent from the initial weight gain, but may be related to a greater volume and intensity of training that can be achieved. There is no definitive evidence that Cr supplementation causes gastrointestinal, renal and/or muscle cramping complications. The potential acute effects of high-dose Cr supplementation on body fluid balance has not been fully investigated, and ingestion of Cr before or during exercise is not recommended. There is evidence that medical use of Cr supplementation is warranted in certain patients (e.g.. neuromuscular disease); future research may establish its potential usefulness in other medical applications. Although Cr supplementation exhibits small but significant physiological and performance changes, the increases in performance are realized during very specific exercise conditions. This suggests that the apparent high expectations for performance enhancement, evident by the extensive use of Cr supplementation, are inordinate.
Med Sci Sports Exerc. 2000 Mar;32(3):706-17
Acute creatine loading increases fat-free mass, but does not affect blood pressure, plasma creatinine or CK activity in men and women.
Creatine monohydrate (CrM) administration may enhance high intensity exercise performance and increase body mass, yet few studies have examined for potential adverse effects, and no studies have directly considered potential gender differences. PURPOSE: The purpose of this study was to examine the effect of acute creatine supplementation upon total and lean mass and to determine potential side effects in both men and women. METHODS: The effect of acute CrM (20 g x d(-1) x 5 d) administration upon systolic, diastolic and mean BP, plasma creatinine, plasma CK activity, and body composition was examined in 15 men and 15 women in a randomized, double-blind experiment. Additionally, ischemic isometric handgrip strength was measured before and after CrM or placebo (PL). RESULTS: CrM did not affect blood pressure, plasma creatinine, estimated creatinine clearance, plasma CK activity or handgrip strength (P < 0.05). In contrast, CrM significantly increased fat-free mass (FFM) and total body mass (P < 0.05) as compared with PL, with no changes in body fat. The observed mass changes were greater for men versus women. CONCLUSIONS: These findings suggest that acute CrM administration does not affect blood pressure, renal function or plasma CK activity, but increases FFM. The effect of CrM upon FFM may be greater in men as compared with that in women.
Med Sci Sports Exerc 2000 Feb;32(2):291-6
Creatine supplementation does not affect kidney function in an animal model with pre-existing renal failure.
BACKGROUND: Creatine is widely used as an ergogenic substance among athletes. Safety of prolonged creatine intake has been questioned, based upon case reports and animal data. We investigated the effect of prolonged creatine ingestion on renal function in animals with normal kidney function or pre-existing kidney failure, respectively. METHODS: Male Wistar rats were randomly allocated to four experimental groups: (i) sham-operated, control diet; (ii) sham-operated, creatine-supplemented diet (2% w/w (0.9+/-0.2 g creatine/kg body weight/day)); (iii) two-thirds nephrectomized, control diet; and (iv) two-thirds nephrectomized, creatine supplemented diet. Glomerular filtration rate was determined using inulin and creatinine clearance, together with albumin excretion, urea clearance, muscle and serum creatine and serum cystatin C concentrations. RESULTS: In contrast to previous reports, no detrimental effects of creatine supplementation on the renal function indices were observed in two-thirds nephrectomized or sham-operated animals. No differences were observed in inulin (0.28+/-0.08 vs 0.25+/-0.08 ml/min/100 g; P=NS) or creatinine clearance rates. Serum cystatin C concentration, urinary protein excretion and albumin and urea clearance were comparable between creatine-supplemented and control-diet fed animals in both sham-operated and two-thirds nephrectomized animals. Serum creatine and intramuscular total creatine concentrations were higher in creatine-supplemented groups (P<0.05). CONCLUSIONS: Creatine supplementation at a dosage of 2% w/w for four weeks does not impair kidney function in animals with pre-existing renal failure or in control animals.
Nephrol Dial Transplant 2003 Feb;18(2):258-64