Thursday, September 10, 2009

Colloidal silver

Colloidal silver is a liquid suspension of microscopic particles of silver. A colloid is technically defined as particles which remain suspended without forming an ionic, or dissolved solution. The broader commercial definition of "colloidal silver" includes products that contain various concentrations of ionic silver, silver colloids, ionic silver compounds or silver proteins in purified water. Colloidal silver with concentrations of 30 parts per million (ppm) or less are typically manufactured using an electrolysis process, whereas colloidal silver with higher concentrations of 50 ppm or more are usually silver compounds that have been bound with a protein.

Colloidal silver is currently marketed for internal and external use as an alternative medical remedy though there is no scientific evidence of its effectiveness in vivo. Some in vitro studies demonstrate an anti-bacterial effect of electrically generated silver ions although a study of a colloidal silver solution marketed on the Internet showed no such antimicrobial activity. Excessive ingestion of colloidal silver can result in argyria, a cosmetic condition in which the skin irreversibly turns blue or grey.

Historical applications

Silver has had some medicinal uses going back for centuries. In the early 1900s, silver gained regulatory approval as an antimicrobial agent. However, the use of silver diminished with the introduction of antibiotics in the early 1940s. A few prescription drugs containing silver are still available. Prior to 1938, colloidal silver was used as a germicide and disinfectant. Physicians used it as an eyedrop for ophthalmic problems, for various infections, and sometimes internally for diseases such as tropical sprue, epilepsy, gonorrhea, and the common cold.
Current applications

From approximately 1990, especially with the emerging problem of antibiotic resistance , there has been a resurgence of the promotion of colloidal silver as an alternative medicine treatment, marketed with claims that it can prevent or treat numerous diseases. In vitro evidence of an antimicrobial effect of colloidal silver is mixed; one study has found it to lack any antibacterial effect,[5] while others have reported colloidal solutions of 5-30ppm as being effective against staph and e.coli There are no clinical trials showing that any preparation of colloidal silver is effective in vivo.

Colloidal silver products are legally available at health food stores in the United States and Australia and are marketed over the Internet as a dietary supplement. It is illegal in the U.S. and Australia for marketers to make claims of medical effectiveness for colloidal silver, but some websites still list its use for the prevention of colds and flu, and the treatment of more serious conditions such as diabetes, cancer, chronic fatigue syndrome, HIV/AIDS, and tuberculosis, among other diseases. There is no medical evidence that colloidal silver is effective for any of these claimed indications. Silver is not an essential mineral in humans; there is no dietary requirement for silver, and no such thing as a silver "deficiency".

Currently, there are no evidence-based medical uses for ingested colloidal silver. There are no clinical studies in humans demonstrating effectiveness, and a few reports of toxicity. The U.S. National Center for Complementary and Alternative Medicine has issued an advisory indicating that the marketing claims made about colloidal silver are scientifically unsupported, and that the silver content of marketed supplements varies widely and can pose risks to the consumer.

Use as water disinfectant

Electrolytically dissolved silver has been used as a water disinfecting agent. Silver was added as a disinfectant to the drinking water supplies of Russian Mir orbital station and the International Space Station. The World Health Organization includes silver in a colloidal state produced by electrolysis of silver electrodes in water, and colloidal silver in water filters as two of a number of water disinfection methods specified to provide safe drinking water in developing countries. Along these lines, a ceramic filtration system coated with silver particles has been created by Ron Rivera of Potters for Peace and used in developing countries for water disinfection.

Use in horticulture

Silver in ionic solutions like silver thiosulfate and silver nitrate (not suspended elemental silver) has been shown to be an ethylene inhibitor[25] by competing with ethylene for binding sites by the plant receptors. Because of this property, solutions containing silver ions are sometimes used by florists to keep flowers fresh longer [27]. Since ethylene is also involved in the "sexing" of plants, this property of blocking ethylene synthesis is also used for forcing male flowers on female plants.[28] As a result, the use of ionic silver solutions has become popular in cannabis cultivation.

Adverse effects and interactions
Main article: Argyria

Chronic intake of silver products, especially colloidal silver, can result in silver or silver sulfide particles in the skin, a condition known as argyria, one symptom of which is blue or gray discoloration of the skin; similarly, it can lead to silver in the eye (argyrosis) and in other organs. The discoloration occurs when silver is deposited in the skin and then darkened by sunlight, just as silver particles in photographic film darken when exposed to sunlight. Localized argyria can occur as a result of topical use of silver-containing remedies, while generalized argyria results from the ingestion of colloidal silver. Argyria is usually permanent, and there is no known effective treatment; the only practical method of minimizing its cosmetic disfigurement is avoiding the sun. While argyria is usually benign and limited to skin discoloration, there are isolated reports of more serious neurologic, renal, or hepatic complications. A death has been reported in the medical literature as a result of colloidal silver use; in that case, a 71-year-old man developed status epilepticus which the authors felt was due to silver toxicity.

A number of case reports describe argyria after ingestion of colloidal silver marketed as an alternative-medicine treatment.[17][30][31][33] Colloidal silver may theoretically reduce the absorption of some medications, including tetracycline and quinolone antibiotics and penicillamine, thereby reducing the effectiveness of those medications.

Government regulation

In August 1999, the U.S. Food and Drug Administration (FDA) banned colloidal silver sellers from claiming any therapeutic or preventive value for the product, noting that colloidal silver was being marketed for numerous diseases without evidence of safety or effectiveness. The product now has the status of a dietary supplement in the US; it can be promoted with general "structure-function" claims, but cannot be marketed as preventing or treating any illness. Following this ruling, the FDA has issued numerous warnings to Internet sites which have continued to promote colloidal silver as an antibiotic or for other medical purposes.

In 2002, the Australian Therapeutic Goods Administration (TGA) found that there were no legitimate medical uses for colloidal silver and no evidence to support its marketing claims. Given the associated safety risks, the TGA concluded that "efforts should be made to curb the illegal availability of colloidal silver products, which is a significant public health issue.