Americans are not accustomed to considering the liver as a factor in health and disease. We fear conditions such as heart disease, obesity and cancer, but seldom do we link any of these to derangements in the liver. This is unfortunate because hepatic functions rule much of the body. The liver is the largest organ in the body. It is so large, in fact, that it fills the entire upper right-hand side of the abdominal cavity and spills over into the left-hand side. The bulk of the liver consists of many small functional units called liver lobules; in humans there may be as many as 100,000 lobules constituting the mass of the organ. The size and complexity of the liver is related to the multitude of roles that this organ plays in the body. Considering the indispensable quality of these roles, it is fortunate that nature has built considerable redundancy into the organ. As much as 60 percent of the liver can be damaged without causing obvious illness and, given the proper care, even a severely damaged liver can largely regenerate itself.
Functions Of The Liver1
Most conspicuous among the functions of the liver is the secretion of bile. Bile goes first into the gallbladder and then into the small intestine, where it acts to break fat globules into small droplets. The role of bile in the body is more complex than this, however, and is related to the liver’s other functions. These can be divided between the storage and filtration of blood, on the one hand, and involvement in the majority of all of the body's metabolic functions, on the other hand. The range and significance of the liver’s participation in metabolic functions can be seen even from the peculiar fact that the hepatic portal vein delivers blood directly from the gastrointestinal tract to the liver before this nutrient-rich blood is distributed to the rest of the body. All liver cells are continuously in contact with blood from the portal vein. In other words, the liver is to the metabolic system what the heart is to the circulatory system.
Blood equivalent to just under 30 percent of the heart’s resting output constantly flows through the liver via the portal vein and the hepatic artery. Cirrhosis of the liver, which can result from alcoholism or any number of toxic and viral causes, radically restricts portal vein blood flow because fibrous tissues constrict around the veins that run through the liver. As much as 10 percent of all blood typically is found in the liver and the liver can expand to hold even an entire liter upon demand. Similarly, roughly 50 percent of the lymph formed in the body at rest originates with the liver.
As might be expected from the degree of blood flow through the liver, detoxification is a primary role of the organ. Large macrophages lining liver tissues routinely capture and degrade the bacteria almost always found in the blood of the portal vein, i.e., in blood that has just come from the digestive tract. The liver likewise detoxifies and excretes into the bile excess and degraded hormones, poisons and drugs such as antibiotics, and the end products of red blood cell disintegration. Indeed, one of the great benefits of soluble and semi-soluble fibers in the diet is that these capture and prevent the reabsorption of many toxins that had been disposed of by the liver via bile salts.
The two preceding functions of the liver, bile secretion and blood filtration, thus are quite closely linked. The third or metabolic function of the liver is as varied as are the first two. This function encompasses the metabolism of carbohydrates, fats and proteins as well as the activation and storage of many vitamins.
Normal blood glucose levels are maintained primarily by the liver. Although a certain amount of the glucose entering the system after meals is disposed of via the lean peripheral tissues, for the most part it is the liver that either dispenses or withdraws sugar from the blood as needed. This means that it is the liver that produces and stores the preponderance of glycogen found in the body, which converts fructose to glucose, and which creates new glucose from non-carbohydrate sources when blood glucose levels fall too low. It also is the liver that is the site of the production of most of the aspartate, succinate, and other by-products of the Citric Acid or Krebs Cycle for use in the body.
With regard to fats, the liver performs a number of special operations. For instance, immediately following meals, the chief site for the creation of fat from excess calories derived from carbohydrates and proteins is the liver. Preformed fats consumed in meals, of course, are digested and assimilated through the action of bile, as already mentioned. The lipoproteins that carry all of these fats throughout the body for storage, for the production of hormones and for energy likewise come from the liver. The cholesterol and the phospholipids found in every cell in the body are largely synthesized in the liver. Finally, much of the oxidation of fatty acids for energy takes place in the liver.
Protein metabolism in the liver may actually be more important to sustained good health than either carbohydrate or fat metabolism. Proteins are necessary for the integrity of all tissues, but this role comes at a high price. The degradation of proteins produces ammonia, which is highly toxic even in small amounts. It is the liver that removes ammonia from the blood and transforms it into urea for disposal by the kidneys. Similarly, it is the liver that deconstructs proteins so that they can be used as sources of energy. The amount of such degradation that takes place outside of the liver is of little consequence to the body. Virtually all of the numerous proteins found in the blood come from the liver, and these proteins control clotting, blood volume and other such duties. Finally, nonessential amino acids and other compounds constructed from amino acids are usually formed in the liver.
Quite a number of nutrients are stored in the liver. Iron is the best known of these, but the vitamins A, B-12 and D also are stored in this organ. As a related function, it should be remembered that many vitamins can be used by the body only after they have been converted into their co-enzymatic forms, and these conversions typically take place either directly in the liver or through one of the liver’s actions.
Optimization Of Liver Functions
Since the liver performs so many roles, it is critical that the vitality of the organ be carefully nurtured. This nurturing consists of three facets. First, it is important to protect the liver from the effects of the various toxins with which it routinely comes into contact. These toxins have many sources. Bacteria and viruses produce toxins, as does the immune system when it combats these. The ammonia from protein metabolism is an ever-present toxin. And then there are environmental toxins, some natural and some produced by modern technology. The former include the aflatoxins found in virtually all peanut products, whereas the latter include pesticide residues, dioxin from paper production and other sources, and the multitude of halogenated products and phthalates now found everywhere, e.g., as plastics.
A second approach to improving liver function is to encourage the secretion of bile by the liver and then the promotion of bile outflow from the gallbladder. The items involved usually are lumped together under the name of “lipotropics.” These can be divided between choleretics or items encouraging the production of bile, and cholagogues, substances that lead to the release of bile from the gallbladder. Inasmuch as toxins are often removed from the body via the bile and, likewise, the inability of the liver to detoxify properly can lead to the infiltration of fatty deposits into the liver, both of these approaches are needed to safeguard liver health. Both the basic bile secretory functions and attendant removal of bile by the gallbladder must be addressed.
The third approach to improving liver function involves adding substances to the diet that aid the liver in its actions of transforming proteins, fats and carbohydrates, in changing vitamins into their actives forms, and in pursuing its other metabolic functions.
Common Liver Protectants
Milk Thistle Extract/Silymarin
Silymarin refers to the most active three components of milk thistle. Milk thistle has long been used traditionally to protect and treat the liver, where it increases the content of the antioxidant enzyme glutathione (GSH). Silymarin neutralizes toxins and is known to help regenerate damaged livers and to improve liver function.2 Silymarin can take over many of the detoxification functions of the liver. Since there can be a rebound effect similar to that found with vitamin C after long and extensive use of silymarin, it is advisable to cut back usage slowly after a course of treatment.
Dandelion Root Extract
Dandelion root is a classic liver tonic. Dandelion is a “bitter” herb that clears the liver and improves its functions. The presence of fats in the diet and likewise the day-to-day production hormones that are made from fats represent heavy demands placed upon the liver, which must routinely transforms the fats and deactivate the breakdown products of the hormones. In women inadequate liver function plays a primary role in PMS and in difficult menopause. In men the results of poor liver function are just as destructive, e.g., constipation, heart disease and related problems, perhaps increased/premature hair loss. Dandelion is noted for its ability to aid in a multitude of disorders involving the liver.3
One active constituent of barberry is berberine. Traditionally, barberry has been used to treat high fevers, jaundice and chronic dysentery. The alkaloid possesses antibacterial and antifungal aspects, including actions against Candida albicans. In general, berberines are considered to have a soothing effect upon the mucous membranes, including those that line the gastro-intestinal tract. Barberry promotes both the secretion of bile and its elimination via the gallbladder.4
Licorice root is characterized by a remarkably extensive number of healing properties. With regard to the liver, the glycyrrhizin content represents the root’s chief benefit. Glycyrrhizin is known to protect against toxin-induced liver damage and to improve the response to viral hepatitis. Unwanted aldosterone effects from the acid are rare from extracts and generally are limited to licorice-flavored sweets eaten in excess.5
Cynarin and other caffeylquinic acids in the artichoke promote bile secretion and flow. Artichoke extracts are used extensively in Europe to protect the liver against toxins and to encourage the regeneration of the liver after damage. Indeed, artichoke extracts have been shown to lower cholesterol and triglyceride levels in humans.6
Fumitory regularizes the flow of bile from the gallbladder and also stimulates the secretion of bile by the liver. It has long been used to improve response to obstructed bile flow, such as nausea and pain from the gallbladder.7
Turmeric/Curcumin A plant related to ginger, turmeric is a source of curcumin. This highly colored pigment possesses strong anti-inflammatory properties comparable to those of hydrocortisone, but without the toxicity. Turmeric has a long historical use in the treatment of liver disorders, including jaundice. Curcumin is a powerful antioxidant and a protectant against toxins. Turmeric also inhibits organisms that cause the inflammation of the gallbladder.8
Bupleurum and Black Radish
These items are among the standards in Asian medicine for treating hepatic disorders. They commonly are used in cases of chronic hepatitis. They are said to “drain excess fire” from the liver, improve jaundice and generally to promote the excretion of bile. Specially prepared radish is a standard for liver problems in India as well as in China and Japan.9
Lipoic Acid, also known as thioctic acid, is a “conditional” vitamin that can be made in limited quantities by the body. Animal experiments have yielded interesting results. Lipoic acid can positively influence some aspects of diabetes, including the neuropathies associated with the disease. As is true of L-carnitine, lipoic acid appears to have immune enhancing properties and also to be able to help protect against atherosclerosis. It contains sulfur and is closely linked to the functions of alpha-ketoglutarate and other alphaketoacids in energy production cycles. Lipoic acid, through its role in the functioning of acetyl-coenzyme A leading into the Citric Acid Cycle, may improve the functioning of the B vitamins and energy levels. This central role in the basic energy production cycle likely serves to shunt calories into activity and away from storage as fats that so often characterizes reduced metabolism.10 Only trace amounts of lipoic acid are needed by the body, yet by improving the liver’s activities in key metabolic pathways, this substance may encourage the more productive use of other nutrients.
The liver is a centrally important organ in digestion, the clearance of toxins, and basic metabolism. Many issues in physiology that often are treated directly with pharmaceuticals might be indirectly and more safely addressed by supporting the functions of the liver. A number of inexpensive and readily available herb and other natural compounds can be used for these purposes.
- These points are aspects of general anatomy and physiology, for which see: Cecil Textbook of Medicine (fifteenth edition, 1979) under various headings; Arthur C. Guyton, Textbook of Medical Physiology (eighth edition, 1991) 744ff; Gary A. Thibodeau, Structure & Function of the Body (ninth edition, 1992) 201–2, 307–9, 320–1.
- Planta Medica 50 (1984) 248–50; Plant Flavonoids in Biology and Medicine (1986) 545–58.
- Michael Weiner, Weiner’s Herbal (Mill Valley, CA: Quantum Books, 2nd edition, 1990).
- British Herbal Pharmacopoeia (British Herbal Medical Association, 1983). 5. H. Suzuki, et al., “Effects of glycyrrhizin on biochemical tests in patients with chronic hepatitis,” Asian Medical Journal 26 (1984) 423–38; Y. Kiso, et al., “Mechanism of antihepatotoxic activity of glycyrrhizin,” Planta Medica 50 (1984) 298–302.
- T. Maros, et al., “The effects of Cynara scolymus extracts on the regeneration off the rat liver,” Arzneim-Forsch. 16 (1966) 127–9 and 18 (1968) 884–6; on hyperliperdemia, see 25 (1975) 1,311–14.
- P. Forgacs, et al., Pl. Med. Phyt. 16 (1982) 99ff.
- Y. Kiso, et al., “Antihepatotoxic principles of curcuma longa rhizomes,” Planta Med 49 (1983) 185–7.
- Oriental Materia Medica.
- Maria C. Linder, Nutritional Biochemistry and Metabolism (Elsevier, 1991) 122; H. Ohmari et. al., I. “Augmentation of the antibody response by lipoic acid in mice.” II. “Restoration of the antibody response in immunosuppressed mice,” Japanese Journal of Pharmacology 42 (1986) 275–80; G. Sachse and B. Willms, “Efficiency of thioctic acid in the therapy of peripheral diabetic neuropathy.” Hormone and Metabolic Research 9, Supplement (1980) 105; J.C.H. Shih, “Atherosclerosis in Japanese quail and the effect of lipoic acid.” Fed. Proc. 42 (1983) 2494–7.
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Dallas Clouatre, PhD
Dallas Clouatre, Ph.D. earned his A.B. from Stanford and his Ph.D. from the University of California at Berkeley. A Fellow of the American College of Nutrition, he is a prominent industry consultant in the US, Europe, and Asia, and is a sought-after speaker and spokesperson. He is the author of numerous books. Recent publications include "Tocotrienols in Vitamin E: Hype or Science?" and "Vitamin E – Natural vs. Synthetic" in Tocotrienols: Vitamin E Beyond Tocopherols (2008), "Grape Seed Extract" in the Encyclopedia Of Dietary Supplements (2005), "Kava Kava: Examining New Reports of Toxicity" in Toxicology Letters (2004) and Anti-Fat Nutrients (4th edition).