What are beta-glucan's therapeutic uses?
The term “beta-glucan” refers to a class of soluble fibers found in many plant sources. The best documented use of beta-glucan involves improving heart health; the evidence for benefit is strong enough that the U.S. Food and Drug Administration (FDA) has allowed a “heart healthy” label claim for food products containing substantial amounts of beta-glucan. Much weaker evidence supports the potential use of certain beta-glucan products for modifying the activity of the immune system.
Beta-glucan is not an essential nutrient. It is found in whole grains (especially oats, wheat, and barley) and fungi such as baker’s yeast, Coriolus versicolor, and the medicinal mushrooms maitake and reishi.
Different food sources contain differing amounts of the various chemical constituents collectively called beta-glucan. Grains primarily contain beta-1,3-glucan and beta-1,4-glucan. Fungal sources contain a mixture of beta-1,3-glucan, and purified products containing only the 1,3 form are also available.
For improving total and LDL cholesterol, studies have found benefit with beta-glucan at doses ranging from 3 to 15 grams (g) daily. However, benefits have been seen more consistently at the higher end of this range, and one carefully designed study found no benefit at 3 g daily.
Beta-glucan products can contain molecules of various average lengths (molecular weight). Some manufacturers claim superior benefits with either high or low molecular weight versions. However, one study failed to find any difference between high molecular weight and low molecular weight beta-glucan for normalizing cholesterol and blood sugar levels.
A substantial, if not entirely consistent, body of evidence indicates that beta-glucan, or foods containing it (especially oats), can modestly improve a person’s cholesterol profile. The most reliable benefits have been seen regarding levels of total cholesterol and LDL (low-density lipoprotein, or bad) cholesterol. Modest improvements of up to 10 percent have been seen in studies. Possible improvements in HDL (high-density lipoprotein, or good) cholesterol have been seen only inconsistently. It is thought that beta-glucan reduces cholesterol levels by increasing excretion of cholesterol from the digestive tract. This affects two forms of cholesterol: cholesterol from food, and, more important, cholesterol from the blood “recycled” by the liver through the intestines. However, virtually all studies involved oats and were conducted by manufacturers of oat products; independent confirmation remains minimal.
Beta-glucan may also modestly improve blood pressure levels, though not all studies agree. In addition, beta-glucan may help limit the rise in blood sugar that occurs after a meal. This could, in theory, offer heart-healthy benefits, especially in people with diabetes.
The other primary proposed use of beta-glucan products involves effects on the immune system. Test tube, animal, and a few controlled studies in humans suggest that beta-glucans can alter various measurements of immune function. In the alternative medicine literature, these effects are commonly summarized as indicating that beta-glucan is an “immune stimulant.” This description, however, is an oversimplification. The immune system is extraordinarily complicated and, as yet, incompletely understood. At the current level of scientific understanding, it is not possible to characterize the effects of beta-glucan more specifically than to say that it has “immunomodulatory” actions, or that it is a “biological response modifier.” These intentionally unsensational terms indicate that it is known that beta-glucan affects (modulates) immune function, not that it improves immune function. Some of the immune-related effects seen in studies include alterations in the activity of certain white blood cells and changes in the levels or actions of substances, called cytokines, that modulate immune function.
Based on these largely theoretical findings, as well a small number of very preliminary human trials, various beta-glucan products have been advocated for the treatment of conditions as diverse as allergic rhinitis, cancer, infections, and sepsis (overwhelming infection following major trauma, illness, or surgery). However, the evidence for actual clinical benefit remains highly preliminary.
One study failed to find that beta-1,3-glucan (in topical gel form) was helpful for treatment of actinic keratosis, a form of sun-induced precancerous changes seen in aging skin. Another study found that it had no significant effect on periodontal disease (gingivitis), an inflammation of the gums caused by bacteria found in dental plaques.
Beta-glucan, as a substance widely present in foods, is thought to have a high margin of safety. However, if it really does activate the immune system, harmful effects are at least theoretically possible in people with conditions in which the immune system is overactive. These include multiple sclerosis, lupus, rheumatoid arthritis, asthma, inflammatory bowel disease, and hundreds of others conditions. In addition, people taking immunosuppressant drugs following organ transplantation surgery could, in theory, increase their risk of organ rejection. However, there are no reports as yet to indicate that any of these hypothetical problems have actually occurred. Maximum safe doses in young children, pregnant or nursing women, or people with severe liver or kidney disease have not been established.
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