At a glance
- Oral colloidal silver products are purported to be effective against viruses, bacteria, cancer, diabetes, and even HIV/AIDS. There are no clinical data to support these claims or validate the safety of colloidal silver use.
- Silver accumulation in body tissue can be fatal.
- Side effects from using products containing colloidal silver may include neurologic problems (e.g., seizures), kidney damage, stomach distress, headaches, fatigue, and skin irritation.
Colloidal silver, taken internally, is one of the newest applications on the medical landscape. However, the move from topical to oral silver use has had a detrimental effect on safety and efficacy.
Medical uses of silver have been documented in early Egyptian, Greek, and Roman society.1 Silver’s potential as an antibacterial agent began with the advent of silver foil dressings. In the 1960s, topical silver sulfadiazine ointment was developed; it is still the number one burn treatment in the United States.2 More recently, silver-coated vascular catheters and heart valves have become commonplace because of the element’s ability to reduce associated infections.2
Science
In its stable state, silver is a neutral element, but silver can also exist as a positively charged ion. In this form, the metal is antibacterial.2 Though no research has proven silver’s mechanism of action against bacteria, the positively charged silver ions are thought to bind to the bacterial DNA and prevent cell reproduction.2 Silver ions also bind to cell walls and other cellular organelles, killing the bacteria outright or preventing replication. This multifaceted attack makes bacterial resistance to silver unusual.3
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Advertising claims for oral colloidal silver products proclaim efficacy against viruses, bacteria, cancer, diabetes, and even HIV/AIDS. To date, however, there are no human clinical data to either support these claims or validate the safety of colloidal silver use.4
Roughly 10% of ingested silver is absorbed in the small intestine. The absorbed silver binds with blood proteins (usually albumin) to form silver-protein complexes, which are transported through the body and deposited in the skin, liver, spleen, and adrenals. The complexes also penetrate the blood-brain barrier, leading to depositions of silver in neuronal and glial cells of the central nervous system. Silver is also toxic to bone marrow and may be associated with agranulocytosis.5
Animal studies have shown that silver accumulates in body tissues and is cleared very slowly by natural elimination methods. One human patient known to have ingested silver was found to be excreting silver in the urine three months after he stopped taking the element .5
The Environmental Protection Agency (EPA) considers silver a toxic substance and has established an oral reference dose (RfD) based on the amount of silver expected to cause cellular necrosis. The current daily RfD for silver is approximately 5 µg/kg of body weight.5 Doses that meet or exceed this level should be considered potentially lethal.
Much of the danger surrounding colloidal silver is the inability to know the exact concentration of actual silver in the solution and the silver particle size. The rate of systemic absorption of silver is highly variable and depends on the particle size and whether or not the silver is truly in an ionized solution or bound to a carrier molecule.5 In one sample of commercially available colloidal silver tested by the EPA, a concentration of 5 parts per million was found in one teaspoon of solution.5 One ounce of this preparation would contain 0.15 mg of silver. According to the EPA’s RfD of .35 mg for a 160-lb adult, daily consumption of this amount would still not reach dangerous levels.5 However, since the absorption, binding, and elimination of silver is so highly variable, the potential exists for a toxic level to accumulate in tissues if dosing is prolonged over weeks and months.
Safety and interactions
Silver accumulation in body tissue can have fatal consequences. The least dangerous but most obvious side effect is argyria, which is brought on by silver accumulation in the skin and causes a bluish tint. Argyria is permanent and cannot be treated or reversed.6
Additional side effects from using products containing colloidal silver may include neurologic problems (e.g., seizures), kidney damage, stomach distress, headaches, fatigue, and skin irritation. Colloidal silver may interfere with the body’s absorption of some drugs, such as penacillamine, quinolones, tetracyclines, and thyroxine.6 Pregnant women should never consume colloidal silver because it can cause developmental abnormalities in the fetus.7
In 1999, the FDA stipulated that no OTC colloidal silver has any form of approval as a medicinal compound.8 The FDA and the Federal Trade Commission have also issued warnings to Web sites that market colloidal silver with druglike claims (i.e., claims that their products diagnose, treat, cure, or prevent disease).6
Do not confuse oral colloidal silver with any of the very safe and effective topical or implanted products on the market; these agents have tremendous impact on the growing levels of microbial resistance to standard antibiotic therapies.
Summary
The use of silver products must remain under the guidance of a clinician. The risk/benefit ratio of current colloidal silver products is a very poor gamble and one that clinicians should urge patients not to take. Given the surge in popularity of alternative therapies, the presence of products containing this supplement on the shelves of America’s retail outlets is most unfortunate. There is no clinical indication for its use.
Wound-care products containing silver are extremely useful in combating infections and must not be classified in the same category as colloidal silver. Colloidal silver is a product clinicians must be very clear about. Make sure patients understand its lack of utility and potential for danger.
References
1. Alexander JW. History of the medical use of silver. Surg Infect (Larchmt). 2009;10:289-292.
2. Ovington LG. The truth about silver. Ostomy Wound Manage. 2004;50(9A Suppl):1S-10S.
3. Chopra I. The increasing use of silver-based products as antimicrobial agents: a useful development or a cause for concern? J Antimicrob Chemother. 2007;59:587-590.
4. Memorial Sloan-Kettering Cancer Center. Colloidal silver.
5. U.S. Environmental Protection Agency. Silver (CASRN 7440-22-4).
6. National Center for Complementary and Alternative Medicine. Colloidal silver products.
7. Fung MC, Bowen DL. Silver products for medical indications: risk-benefit assessment. J Toxicol Clin Toxicol. 1996;34:119-126.
8. Federal Register. Over-the-counter drug products containing colloidal silver ingredients or silver salts. 1999;64:44653-44658.
All electronic documents accessed October 9, 2009.
