Winter 2000 Issue — L-Carnitine, the Primordial Nutraceutical Ingredient

Dr Martin Fuhrmann / P. Gaynor

Lonza

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1. Introduction

The term Neutraceutical was originally coined by Dr Stephen DeFelice in the late 1980s, referring to "any substance that is a food or part of a food and provides medical or health benefits, including the prevention and/or treatment of disease". A more recent definition subdivides nutraceutical foods into 3 distinct categories:

• Dietary supplements which consist of vitamins, minerals, herbs and other food supplements
• Food products for particular nutritional use, e.g. infant formulas, diabetic foods, as well as products for enteral and clinical nutrition
• Functional foods that provide benefits beyond basic nutrition.

Many people may be unaware of the fact that the term Nutraceutical was originally coined around one nutraceutical ingredient and its health enhancing properties: L-Carnitine. Currently, L-Carnitine, or its stable salt forms, e.g. L-Carnitine L-tartrate are key or sole components of numerous dietary supplement products that are offered throughout the world for cardiovascular health, weight management and sports performance. Moreover, since the early 1980s, L-Carnitine has been routinely added to infant formulas, especially to all preparations based on soy protein. L-Carnitine is also used in dietetic or clinical foods, for instance to supplement L­Carnitine losses incurred through dialysis procedures.
A host of research articles and numerous clinical studies document the beneficial effects of L-Carnitine supplementation. While nowadays many substances are discussed as nutraceuticals, L-Carnitine is undoubtedly unique in terms of its physiological functions, its numerous health-enhancing benefits, its suitability for food processing, and safety, thus making the substance a prime candidate for the development of new functional foods.

2. L-Carnitine: A naturally occurring nutrient

L-Carnitine may be defined as a conditionally essential nutrient naturally found within the human body. It is also described as an amino acid-like and vitamin B-like substance. L­Carnitine is supplied to the human body via both food intake and endogenous synthesis in the liver and kidney. Dietary sources of L­Carnitine are confined mainly to foods of animal origin, particularly red meat. Endogenous synthesis requires the presence of lysine, methionine, Vitamin C, Vitamin B, niacin and iron. As a consequence, L­Carnitine levels in the body are greatly dependent on individual nutritional habits, with an obvious risk of functional deficiency.

3. Key metabolic functions of L-Carnitine

Transport of long-chain fatty acids through the mitochondrial membrane: L-Carnitine plays a crucial role in facilitating the generation of energy from fat. This process ß-oxidation requires that fatty acids be transported from the cytosol of the cell intc the mitochondria, these are the organelles within the cell where energy production ultimately takes place. Long chain fatty acic.c by themselves are unable to penetrate the inner mitochondrial membrane, to be accessible for ß-oxidation. L-Carnitine acts as a carrier for these molecules; only in the form of acyl-carnitine esters can they be shuttled into the mitochondria by a specific transport system.

Detoxification:

A secondary but nevertheless crucial function of L-Carnitine is to shuttle excess acyl- and acetyl-residues from inside the mitochondria back to the cytosol and from there to the bloodstream. This action is important for the preservation of membrane integrity and furthermore it generates free coenzyme A (CoA) which is essential for undisturbed energy (ATP) production within the mitochondria. Free CoA is readily available under strictly aerobic conditions since the acetyl-CoA generated by ß-oxidation is immediately processed through the respiratory chain. If however the anaerobic threshold is passed, aceptyl- CoA accumulating, thus limiting the availability of free CoA. L-Carnitine will now act as a buffer for excess acetyl molecules, thus generating the free CoA necessary for continuous energy production.

4. Nutraceutical benefits of L-Carnitine

Cardiovascular Health:

The maintenance of cardiovascular health is one of the key concerns of our times. The scientific evidence which supports the beneficial role of L­Carnitine in cardiovascular well-being is compelling. On average, the heart obtains 70% of its energy requirement from the burning of fatty acids and since L-Carnitine is central to the formation of energy from fat, the heart is consequently dependent upon L­Carnitine for most of its energy production. Myocardial L-Carnitine levels were found to be reduced in heart failure patients, and L­Carnitine supplementation was reported to alleviate symptoms of myocardial ischemia such as angina pectoris (chest pain associated with inadequate blood flow to the heart muscle cells). L-Carnitine supplementation is also helpful for maintaining healthy cholesterol levels.

Sports Performance:

For sports supplements, L­Carnitine is rather unique since it is reported that this nutraceutical ingredient is of benefit for both endurance-trained athletes and ambitious amateurs or 'weekend warriors'. In endurance-trained athletes, L-Carnitine can significantly increase VO2max which is an indicator of endurance performance. Additionally, it can delay the onset of fatigue and induce a glycogen sparing effect. In untrained individuals, supplemental L­Carnitine has again been shown to delay the onset of fatigue, and to reduce the pain and tenderness frequently experienced after unaccustomed exercise. Due to its training-like effects, L-Carnitine is rapidly becoming the nutraceutical of choice among 'weekend warriors'. Apart from the traditional tablets and capsules, L-Carnitine and the non­hygroscopic L-Carnitine Tartrate are now incorporated into numerous sports drinks, meal replaces and energy bars.

Weight Management:

As a component of a weight management program which involves healthy eating habits and moderate exercise, L­Carnitine supplementation can be of significant benefit, as compared to a regime which involves only healthy eating and moderate exercise. As a weight management nutraceutical, L-Carnitine has a number of advantages: apart from its demonstrated effectiveness: first and foremost it is safe and since it is naturally found within the human body, it is a substance with which the body is already familiar.

Infant Nutrition:

L-Carnitine is considered to be a conditionally essential nutrient for babies because their capacity for endogenous synthesis is not yet fully developed, thus they must obtain L-Carnitine through their diet. This is especially important for infant formulas based on soy protein. As mentioned above, L-Carnitine is now routinely added to infant formula, thus highlighting both the importance and the safety of this nutraceutical.

Vegetarians:

Since L-Carnitine is primarily found in meat and meat products, vegetarians have a significantly reduced dietary intake of L-Carnitine and thus are at risk of missing out on the tremendous health benefits of this nutraceutical. L-Carnitine is ideal for inclusion into functional foods designed for the vegetarian consumer, such as soy cheese, soy hot-dogs and soy burgers.

5. L-Carnitine and Food Processing

The physical properties of L-Carnitine (free) base and particularly, L-Carnitine L-Tartrate make these substances extremely suitable for food processing. Both products are bright white, highly water soluble and heat stable. One drawback of L-Carnitine base is its extreme hygroscopicity (it actively absorbs moisture) which leads to various difficulties for manufacturers of tablets and capsules. Stable, non-hygroscopic salt forms such as L­Carnitine L-tartrate or L- Carnitine magnesium citrate overcome these problems, and are ideal for all solid formulation or applications.

6. Dosage and Safety Considerations

With a balanced, non-vegetarian diet, the daily uptake of L-Carnitine will be app. 200 mg. This amount can also be assumed to be the minimum dosage for avoiding any deficiencies. Under conditions of physiologic stress, such as endurance sports or compromised health, the body's demand may be significantly increased. It should also be noted that red meat, especially mutton contains high amounts of L-Carnitine, more than 200 mg per 100 grams. So diets based on meat will lead to a sizeable uptake of L­Carnitine, possibly in excess of 1 gram per day. The doses generally used in clinical trials are in the region of 2 to 3 gram L-Carnitine per day.

Although L-Carnitine is safe and non-toxic, people with medical conditions should consult their physician physician prior to supplementing with L-Carnitine and embarking on an exercise regime. Only pure L-Carnitine is recommended as a supplement. The racemic mixture DL­Carnitine is to be avoided since D-Carnitine is a metabolic antagonist of L-Carnitine, and was shown to induce serious health effects.

7. Summary

The vitamin-like substance L-Carnitine is a conditionally essential nutrient for man, and is performing key functions in fat metabolism and energy provision. It can be synthesized in the human body, but in man the endogenous biosynthesis is by far not sufficient to cover normal requirements. Our body highly depends on a daily dietary supply of L­Carnitine.
As a nature constituent of all organisms it is found in varying concentrations in different foods. While plant-based foods generally contain very little or no L-Carnitine at all, raw foodstuffs of animal origin (mci. dairy products) are rich in L-Carnitine.

The uptake of L-Carnitine from usual food, together with endogenous biosynthesis is regarded sufficient to cover normal requirements. This is, however, not the case in infants, and also in adults under certain nutritional or physiological conditions, with either a low L-Carnitine supply, or an increased demand. Direct benefits of L-­Carnitine supplementation have been described for numerous such conditions. In every phase of life the human body profits from an adequate L-Carnitine supply which is, however, not always ensured. In such cases the intake of additional L-Carnitine helps the body maintaining health and performance.

Considering its many vital metabolic actions, and its broad range of nutritional benefits, L­Carnitine is a prime ingredient for the development of new nutraceuticals or functional foods.

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