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Monascus purpureus is a yeast, but the name is often used to refer to a type of rice grown with the yeast. This red yeast rice is used in some countries as a natural dietary supplement for reducing a person's cholesterol levels. Red yeast rice contains chemicals called monacolins, which are also produced by pharmaceutical companies. There are side effects associated with the ingestion of monacolins and, as a result, red yeast rice is not recommended for the treatment of high cholesterol, in part because the levels of active chemicals in the rice cannot be standardized.
Red rice yeast has been used in Chinese medicine as far back as 800 A.D. In some Asian countries, red rice yeast is regarded as part of a normal diet. The product is known as zhi tai if it is in a powdered, dried form, and xue zhi kang if it is mixed with alcohol.
The primary monacolin produced by monascus purpureus in red yeast rice is monacolin K, which has the same chemical structure as the pharmaceutical product lovastatin. Lovastatin inhibits cholesterol synthesis in the liver by blocking the action of the enzyme 5-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. Side effects of lovastatin include bloating, gas, heartburn, dizziness, muscle pain or damage, asthma and even kidney damage. People with liver problems, children, and women who are breastfeeding or pregnant should not take red rice yeast.
Monascus purpureus has a clear biological effect on cholesterol levels and the U.S. Food and Drug Administration (FDA) considers several products containing the preparation to be unapproved drugs. As a drug, monascus purpureus has to undergo more stringent tests than those of a mere dietary supplement. Several supplements containing red yeast rice are on the FDA's list of products that may be dangerous for consumers, and the agency has warned against using them.
Although the active ingredients in red rice yeast are pharmacologically active and identical to some pharmaceutically prepared drugs, the major problem with taking monascus purpureus products, apart from the possible side effects, is that the active chemical levels in the products can vary. The variation in the active ingredients and the lack of scientific studies means the effect of the product is not predictable. In addition to this concern, some products contain detectable levels of toxins such as citrinin, a fungus that can be toxic to kidneys and even cause genetic changes in cells at a high concentration.