Diet & Fitness

 

L-carnitine is an amino acid needed to transport fats into the mitochondria (the place in the cell where fats are turned into energy). Adequate energy production is essential for normal heart function. Several studies using 1 gram of L-carnitine two to three times per day showed an improvement in heart function and a reduction in symptoms of angina.^2,3,4Coenzyme Q10 also contributes to the energy-making mechanisms of the heart. Angina patients given 150 mg of coenzyme Q10 each day have experienced greater ability to exercise without experiencing chest pain.⁵ This has been confirmed in independent investigations.⁶

 

People with CHF have insufficient oxygenation of the heart, which can damage the heart muscle. Such damage may be reduced by taking L-carnitine supplements.⁷ L-carnitine is a natural substance made from the amino acidslysine and methionine. Levels of L-carnitine are low in people with CHF;⁸ therefore, many doctors recommend that those with CHF take 500 mg of L-carnitine two to three times per day.

Most L-carnitine/CHF research has used a modified form of the supplement called propionyl-L-carnitine (PC). In one double-blind trial, people using 500 mg of PC per day had a 26% increase in exercise capacity after six months.⁹ In double-blind research, other indices of heart function have also improved after taking 1 gram of PC twice per day.¹⁰ It remains unclear whether propionyl-L-carnitine has unique advantages over L-carnitine, as limited research in animals and humans has also shown very promising effects of the more common L-carnitine.¹¹

L-carnitine is an amino acid important for transporting fats that can be turned into energy in the heart. Clinical trials have reported that taking L-carnitine (4–6 grams per day) increases the chance of surviving a heart attack.^12,13,14 In one double-blind trial, individuals with suspected heart attack were given 2 grams of L-carnitine per day for 28 days.¹⁵ At the completion of this study, infarct size, as well as the number of nonfatal heart attacks, was lower in the group receiving L-carnitine versus the placebo group. Double-blind research using L-carnitine intravenously also shows promise.¹⁶

 

L-carnitine is another supplement that has lowered TGs in several clinical trials.^17,18 However, the effect of carnitine is unpredictable, and some individuals have experienced an increase in triglyceride levels after receiving this supplement.¹⁹ Some doctors recommend 1–3 grams of carnitine per day, in the form known as L-carnitine.

L-carnitine is needed by cells, including heart muscle cells, to metabolize fat into energy, and numerous clinical trials show L-carnitine helps regulate cholesterol levels. A meta-analysis that included findings from 67 randomized controlled trials found L-carnitine appeared to lower total and LDL-cholesterol, increase HDL-cholesterol, and reduce triglyceride levels; however, these benefits disappeared when age, health status, and other parameters of trials and their participants were considered.²⁰ Another meta-analysis that included 55 randomized controlled trials found only doses of L-carnitine higher than 2 grams per day improved total, LDL-, and HDL-cholesterol levels.²¹ Using results from eight randomized controlled trials in a combined total of 508 participants with type 2 diabetes, another meta-analysis found L-carnitine supplementation, at doses of 2–3 grams per day for at least 12 weeks, lowered total and LDL-cholesterol levels.²²

 

In double-blind trials, supplementation with either L-carnitine and propionyl-L-carnitine (a form of L-carnitine) has increased walking distance in people with intermittent claudication. Walking distance was 75% greater after three weeks of L-carnitine supplementation (2 grams taken twice per day), than after supplementation with a placebo, a statistically significant difference.²³ In the study using propionyl-L-carnitine, improvement occurred only in those who could not walk 250 meters to begin with. In that group, maximum walking distance increased by 78% with propionyl-L-carnitine supplementation compared with a 44% increase in the placebo group, also a statistically significant difference.²⁴ The amount of propionyl-L-carnitine used was 1 gram per day, increasing to 2 grams per day after two months, and 3 grams per day after an additional two months, if needed. The results of this trial have been confirmed in a large European trial.²⁵

 

L-carnitine has been given to people with chronic lung disease in trials investigating how the body responds to exercise.^26,27 In these double-blind trials, 2 grams of L-carnitine, taken twice daily for two to four weeks, led to positive changes in breathing response to exercise.

 

In one report, deficient levels of L-carnitine were found in five consecutive people with MVP.²⁸ One of these people was given L-carnitine (1 gram three times per day for four months) and experienced a complete resolution of the symptoms associated with MVP.

 

Deficiency of L-carnitine, an amino acid, is associated with the development of some forms of cardiomyopathy.²⁹ Inherited forms of cardiomyopathy seen in children may be the most responsive to therapy with L-carnitine.^30,31 Whether carnitine supplementation helps the average person with cardiomyopathy remains unknown. Nonetheless, some doctors recommend 1 to 3 grams of carnitine per day for adults of average weight.

 

In one study, 12 people with Raynaud’s disease were given L-carnitine (1 gram three times a day) for 20 days.³² After receiving L-carnitine, these people showed less blood-vessel spasm in their fingers in response to cold exposure.

The amino acid L-carnitine is thought to be potentially helpful for weight loss because of its role in fat metabolism. L-carnitine has been found to reduce fatigue and hunger and improve weight loss effects of fasting.^33,34 Multiple controlled trials and three meta-analyses have shown that supplementing with L-carnitine can lead to small reductions in body weight in people with overweight and obesity.^35,36,37 In a placebo-controlled trial that included 60 overweight women with polycystic ovary syndrome, taking 250 mg of L-carnitine daily for 12 weeks resulted in weight loss, waist circumference reduction, and improved glucose regulation and insulin sensitivity.³⁸

L-carnitine is an amino acid needed to properly utilize fat for energy. By supporting healthy fat metabolism, L-carnitine plays an important role in preserving normal insulin sensitivity and glycemic control.^39,40 People with type 2 diabetes have been found to have lower levels of circulating L-carnitine than healthy people, and in people with type 2 diabetes, lower blood L-carnitine levels are correlated with higher blood glucose and triglyceride levels, lower free radical-quenching capacity, and greater risk of diabetes complications.^41,42 Supplementing with L-carnitine has been shown in multiple human and animal studies to improve glucose tolerance and lipid metabolism in the context of insulin resistance.⁴³ A meta-analysis of randomized controlled trials concluded 2–4 grams of L-carnitine per day can effectively reduce fasting blood glucose, total cholesterol, and LDL-cholesterol levels.⁴⁴ Clinical trials further show the potential for 2–4 grams of L-carnitine per day to augment other therapies for improving metabolism in people with diabetes, including glimepiride, orlistat, sibutramine, simvastatin, and a low-calorie diet.^{45,46,47,48,49} In addition, a placebo-controlled trial found 600 mg per day of L-carnitine alleviated diabetes-related muscle cramps (a form of diabetic neuropathy) in people with type 2 diabetes.⁵⁰

The amino acid L-carnitine has been shown in clinical trials and meta-analyses to improve blood glucose control, insulin sensitivity, weight loss, and lipid metabolism, indicating its potential usefulness in treating metabolic syndrome and reducing cardiovascular risk.^51,52 In one placebo-controlled trial, women with obesity and type 2 diabetes participated in a low-calorie diet program and received 2 grams of L-carnitine per day or placebo for about eight weeks. At the end of the trial, those receiving L-carnitine had greater improvements in blood glucose control, insulin sensitivity, cholesterol and triglyceride levels.⁵³ In an uncontrolled trial, taking 3 grams of L-carnitine daily for three months led to decreased insulin resistance, LDL-cholesterol levels, and body-mass index (BMI), and increased HDL-cholesterol levels in 80 women with polycystic ovary syndrome, a condition associated with metabolic syndrome.⁵⁴

Acetyl l-carnitine is an amino acid compound used to treat conditions affecting the brain and peripheral nervous system. Research reviews have concluded acetyl l-carnitine, in doses of at least 2 grams per day, can relieve pain and improve nerve function in those with diabetic nerve damage (neuropathy).^55,56 A preliminary trial found 500 mg of acetyl l-carnitine three times daily for 24 weeks relieved symptoms of diabetic nerve damage (neuropathy) as effectively as vitamin B12.⁵⁷

In a double-blind study, supplementing with the combination of propionyl-L-carnitine (a form of L-carnitine) and acetyl-L-carnitine (2 grams of each per day) for six months significantly improved erectile function in elderly men with erectile dysfunction associated with low testosterone levels. Propionyl-L-carnitine and acetyl-L-carnitine were significantly more effective than testosterone treatment.⁵⁸

 

L-carnitine is a substance made in the body and also found in supplements and some foods (such as meat). It appears to be necessary for normal functioning of sperm cells. In preliminary studies, supplementing with 3–4 grams per day for four months helped to normalize sperm motility in men with low sperm quality.^59,60 While the majority of clinical trials have used L-carnitine, one preliminary trial found that acetylcarnitine (4 grams per day) may also prove useful for treatment of male infertility caused by low quantities of immobile sperm.⁶¹

In a double-blind study, supplementation with L-carnitine for eight weeks resulted in clinical improvement in 54% of a group of boys with ADHD, compared with a 13% response rate in the placebo group.⁶² The amount of L-carnitine used in this study was 100 mg per 2.2 pounds of body weight per day, with a maximum of 4 grams per day. No adverse effects were seen, although one child developed an unpleasant body odor while taking L-carnitine. Researchers have found that this uncommon side effect of L-carnitine can be prevented by supplementing with riboflavin. Although no serious side effects were seen in this study, the safety of long-term L-carnitine supplementation in children has not been well studied. This treatment should, therefore, be monitored by a physician.

In a double-blind trial, supplementing with L-carnitine resulted in a modest improvement in disease severity in children with autism spectrum disorders. The amount of L-carnitine used was 50 mg per kilogram of body weight per day (half in the morning and half in the evening) for three months.⁶³

In a double-blind study, supplementing with the combination of propionyl-L-carnitine (a form of L-carnitine) and acetyl-L-carnitine (2 grams of each per day) for six months significantly improved erectile function in elderly men with erectile dysfunction associated with low testosterone levels. Propionyl-L-carnitine and acetyl-L-carnitine were significantly more effective than testosterone treatment.⁶⁴

 

L-carnitine is required for energy production in the powerhouses of cells (the mitochondria). There may be a problem in the mitochondria in people with CFS. Deficiency of carnitine has been seen in some CFS sufferers.⁶⁵ One gram of carnitine taken three times daily for eight weeks led to improvement in CFS symptoms in one preliminary trial.⁶⁶ Supplementation with 6 grams of L-carnitine per day for four weeks also improved fatigue in a preliminary study of patients with advanced cancer.⁶⁷ Similar improvements were seen in another study of patients with advanced cancer given up to 3 grams of L-carnitine per day for one week.⁶⁸

L-carnitine, which is normally manufactured by the human body, has been popular as a potential ergogenic aid (i.e., having the ability to increase work capacity), because of its role in the conversion of fat to energy.⁶⁹ However, while some studies have found that L-carnitine improves certain measures of muscle physiology, research on the effects of 2 to 4 grams of L-carnitine per day on performance have produced inconsistent results.⁷⁰ L-carnitine may be effective in certain intense exercise activities leading to exhaustion,⁷¹ but recent studies have reported that L-carnitine supplementation does not benefit non-exhaustive or even marathon-level endurance exercise,^72,73 anaerobic performance,⁷⁴ or lean body mass in weight lifters.⁷⁵

In a double-blind trial, supplementing with L-carnitine (1,050 mg each morning for six months) improved lung function and overall asthma control, compared with a placebo, in Egyptian children with asthma.⁷⁶

 

One controlled trial showed that people who supplement with 3 grams per day L-carnitine for three weeks before engaging in an exercise regimen are less likely to experience muscle soreness.⁷⁷