<body><h1>Carnitine</h1><p><br></p><p> syn. 3-hydroxy-4-trimethylammoniobutanoate syn. Levocarnitine (L-carnitine)</p><div id=’imgblock’><img data-pointer=’9102’/></div><h2> Description: </h2><p> Carnitine is a vitamin or amino acid like compound produced in the body from lysine and methionine. It is found almost exclusively in muscle tissue.194 Carnitine is not directly utilized for the synthesis of tissue proteins like its constituent amino acids. Instead, it plays an important role in the muscle cell energy cycle, where it is involved in the metabolism of fatty acids for fuel. Carnitine is found in a wide variety of foods, although the most prominent dietary sources include meat and dairy products. Since the body can readily manufacture carnitine from common amino acids, it is considered a conditionally essential nutrient, which means that it is essential in the diet only under certain metabolic conditions.195</p><p> <div id=’imgblock’><img data-pointer=’9100’/></div></p><p> Carnitine has a few primary roles with regard to cellular metabolism.196 One is to assist in the transport of long chain fatty acids into the mitochondria of muscle cells. Carnitine does this by binding with long chain fatty acids, forming combined molecules called acylcarnitines that can readily transit the inner mitochondrial membrane. Once inside these cellular energy producers, these fats can be combined with oxygen to yield the most basic cellular energy source, adenosine triphosphate (ATP). The oxidation of fatty acids is a major source of fuel during exercise.197 Carnitine also helps remove short chain fatty acids from the mitochondria, which can inhibit energy metabolism as they accumulate. Additionally, carnitine may serve as an antioxidant, helping to buffer some of the free radical products of cell metabolism.198</p><p> As we age, levels of carnitine tend to decline.199 It is theorized that this may be involved in an age-related reduction of metabolic efficiency. Studies suggest that the supplementation of carnitine (or its derivatives) may improve energy metabolism in the elderly.200 Carnitine supplements might also help treat a number of health conditions, including heart disease, Alzheimer’s disease, HIV infection, diabetes, renal disease, cancer, and male infertility.201 Research in this area is ongoing. Comparative studies suggest that carnitine and acetyl-L-carnitine are similar in their abilities to increase serum carnitine levels, though acetyl-L-carnitine appears to have a broader range of biological activity, particularly in the central nervous system.202</p><p> Given the importance of this nutrient in the muscle cell energy cycle, carnitine has long been the focus of supplementation by bodybuilders and athletes. Clinical studies and anecdotal evidence on such use, however, are highly conflicting. This may be due, in part, to difficulties overcoming the body’s normal regulation of tissue carnitine content.203 This supplement has been shown in some studies to improve performance in individuals with training experience, and thus has achieved the highest level of clinical validation. In a practical sense, however, tangible improvements are inconsistent. It seems most reasonable to conclude that this supplement may offer ergogenic value in situations where minor changes in maximal oxygen consumption could result in significant improvements in competition performance. </p><h2> Promoted Benefits:</h2><p> Carnitine is promoted to increase muscle stamina, and improve overall sports/exercise performance. </p><h2> Clinical Studies: </h2><p> Carnitine has been the subject of extensive clinical study. This ingredient has been shown to improve performance in placebo-controlled studies with trained adults. Its Clinical Support Rating is 5 (5/5).</p><p> One of the most compelling placebo-controlled studies with a positive response examined the effects of both acute and extended supplementation of carnitine in elite male and female athletes (kayak, rowing, and weightlifting).204 All participants were subject to a controlled training and dietary program. Individuals in the extended supplementation group consumed 3 grams of carnitine daily for 21 days. The acute study involved a single dose of 4 grams. Supplemented subjects in the extended group noticed improvements in both the strength index and VO2max (maximal oxygen consumption) scores compared to placebo. There were also metabolic improvements with regard to serum free fatty acids and triglyceride levels. The acute study produced similar improvements in fatty acid and triglyceride metabolism 90 minutes after ingestion, as well as in distal latency (a measure of the time between muscle stimulus and muscle response). A second placebo-controlled study examined the effects of carnitine supplementation on exercise performance in a group of trained endurance athletes.205 Supplementation consisted of 2 grams of carnitine daily for 28 days. Baseline and end of study testing involved 45 minutes of stationary cycling at 66% VO2max. Subjects taking carnitine noticed a statistically significant reduction in respiratory quotient (RQ) compared to those taking placebo, which represents the ratio of carbon dioxide exhaled to oxygen consumed. The RQ helps determine the level and source of energy consumption (fat versus carbohydrate oxidation), and drops as fats become more readily utilized. Although not reaching statistical significance, there was also a strong trend of improvement in VO2max with the use of carnitine. These results suggest a notable improvement in the oxidation of fat for energy during exercise as a result of carnitine supplementation. This is a desirable result for exercise performance, as it can help spare glycogen and ATP reserves. </p><p> Another placebo-controlled study examined the effects of acute carnitine supplementation in a group of moderately trained men.206 Subjects consumed 2 grams of carnitine or placebo one hour prior to exercise. The exercise protocols involved the use of a stationary cycle ergometer, which had its level of resistance increased by 50-W every three minutes until the point of exhaustion. In this study, the supplementation of carnitine was shown to produce statistically significant improvements in VO2max and power output. There were also reductions in total oxygen uptake, carbon dioxide production, pulmonary ventilation, and serum lactate, all suggesting improvements in metabolic efficiency with the supplementation of carnitine.</p><p> We also find performance benefits in a study of carnitine supplementation by a group of elite endurance walkers.207 Subjects consumed four grams of carnitine daily for a period of 4 weeks, and were evaluated during a 120 minute walk at 65% of maximal oxygen consumption (VO2max). The supplementation of carnitine was shown to improve maximal oxygen consumption by 6%. There were, however, no statistically significant changes in blood lactate, ventilation, total oxygen consumption, or respiratory quotient. This study was not placebo controlled.</p><p> In contrast to the above studies, there have been many clinical investigations that have failed to produce statistically significant improvements in exercise performance following carnitine supplementation.</p><p> For example, one study with long distance runners found no improvements in marathon time, carbohydrate metabolism, fat metabolism, or serum lactate following a single dose of 4 grams of carnitine prior to a race.208 There was also no change in a submaximal exercise performance test that was given the day after the race.</p><p> Eight healthy male athletes were given 4 grams daily for 14 days in another study.209 While the supplementation resulted in an increase in the serum level of carnitine, it failed to produce any changes in muscle carnitine concentrations or serum lactate levels. This study was not placebo controlled. </p><p> Another investigation gave 6 grams of carnitine daily for 7-14 days to a group of healthy men.210 Exercise performance was evaluated with 60 minutes of cycling at 70% maximal oxygen consumption. The supplementation of carnitine failed to produce any improvements in respiratory quotient, oxygen consumption, free fatty acids, or glucose utilization during exercise. Muscle carnitine levels did not change.</p><p> Exercise performance was evaluated following carnitine supplementation in another study with a group of elite male swimmers.211 Subject consumed 4 grams of carnitine daily for seven days. In this study, carnitine supplementation did not result in any improvements in swimming performance or lactate concentrations compared to those taking placebo.</p><p> A group of moderately trained men were given 5 grams of carnitine per day for five days in another investigation. Exercise capacity was evaluated before and after supplementation with a stationary cycle ergometer, which was operated for 120 minutes at 50% maximal oxygen consumption. In this study, carnitine failed to produce statistically significant improvements in oxygen consumption or fatty acid turnover.</p><p> There are many additional clinical studies on the effects of carnitine supplementation on exercise performance in healthy adults, with varying results.212 It is unclear if this high level of inconsistency is the result of methodological difficulties (statistical significance can be difficult to reach, especially in studies with trained athletes), dietary or training factors that influence the retention of carnitine in muscle tissue, or a situation where carnitine is only of ergogenic value when used under a very specific set of metabolic or athletic conditions. Further research is needed to better understand the optimal methods for utilizing L-carnitine to improve exercise performance in trained adults.</p><h2> Empirical Evidence: </h2><p> Carnitine is widely available as a stand-alone nutritional supplement. Unfortunately, the feedback on its use as a sport supplement tends to be negative. Most people that invest in carnitine do not find that its use results in noticeable improvements in exercise performance. This is especially true when the desired result is an increase in lean muscle mass or strength, a popular claim used by manufacturers in their advertising. A minority of users, however, do feel that carnitine offers value as a sport supplement, usually with regard to endurance exercise stamina. Given the results of placebo-controlled studies, it is reasonable to conclude that some of these reports are genuine. It may simply be that carnitine is an effective supplement, but only for a subset of users best positioned to notice its benefits, such as runners or other track and field athletes with very specific performance measures to work against. Carnitine has an Empirical Evidence Rating of 2 (2/5).</p><h2> Effective Dosage: </h2><p> Based on clinical studies, a dosage of 2-4 grams per day is recommended. </p><h2> Side Effects / Safety: </h2><p> Carnitine was well tolerated during clinical studies, with few side effects reported. A small percentage of users appear to notice gastrointestinal distress (loose stool, nausea, diarrhea).213 </p><p> </p></body>
