Colloidal gold (CG) is a suspension of microscopic gold particles in a liquid, typically deionized water, and is often sold as a dietary supplement promising various health benefits. Its safety for human consumption is complex and tied directly to its unique physical properties. The perception of gold as an inert metal clashes with the biological activity that emerges when it is reduced to the nanoscale. Understanding the potential toxicity of CG requires examining its composition, the variables influencing its interaction with the body, and the current scientific consensus on its long-term oral use.
What Exactly is Colloidal Gold
Colloidal gold is defined as a sol: a stable suspension of gold nanoparticles in a fluid. These minute particles of elemental gold are dispersed evenly throughout the liquid, not dissolved. The distinguishing feature is the size of the suspended particles, typically between 1 and 100 nanometers (nm).
This nanoscale size differentiates it from chemically inert bulk gold, such as jewelry. Reducing gold to this scale dramatically changes its properties, leading to unique optical characteristics; for example, solutions often appear a vibrant ruby-red color.
Preparation methods, like the Turkevich method, involve the chemical reduction of gold salts using a stabilizer, such as citrate. These stabilizers prevent the particles from clumping and settling, allowing the gold to remain suspended. The type of stabilizing agent and the precise particle size play a role in how the substance interacts with biological systems.
The Spectrum of Gold Toxicity
The toxicity profile of gold nanoparticles is not uniform but exists on a spectrum determined by specific physicochemical factors. The most significant variable is the particle’s size, which dictates how it moves and interacts within the body. Smaller nanoparticles, particularly those under 5 nm, show greater potential for toxicity in laboratory studies than larger particles, likely due to easier interaction with cellular components.
Toxicity risk is also influenced by impurities or stabilizing agents used during synthesis. Coatings like citrate or polymers maintain stability but can alter the gold’s surface chemistry and biological effects. The fate of elemental gold nanoparticles (Au-NP) differs fundamentally from gold ions (Au ions). Ions are rapidly absorbed and distributed widely to organs like the liver, spleen, and kidney, while nanoparticles are absorbed much more slowly.
Dosage and exposure route are also important. While high doses are investigated for medical applications like cancer therapy, commercial dietary supplements contain much lower concentrations. Short-term animal studies using high single oral doses show low acute toxicity, shifting the primary concern to the effects of chronic, low-dose exposure over many years.
Unproven Health Claims and Regulatory Status
Colloidal gold is widely marketed despite the complexities surrounding its safety, often featuring unsubstantiated health claims. Common assertions include enhancing cognitive function, such as improving memory and mental clarity. Other touted benefits relate to purported anti-inflammatory properties, with some manufacturers suggesting it can help manage conditions like arthritis.
These claims are often extrapolated from the use of gold salts, which have a history as anti-inflammatory agents in medicine. However, there is a lack of rigorous, independent evidence supporting these benefits for colloidal gold supplements. To claim treatment, cure, or prevention of a specific disease, a dietary supplement must meet the U.S. Food and Drug Administration’s (FDA) standard of “significant scientific agreement,” which CG does not meet.
Regulatory bodies, including the FDA and the Federal Trade Commission (FTC), have taken action against manufacturers for making unproven disease-related claims. Since CG supplements are not reviewed or approved by the FDA for safety or effectiveness before marketing, consumers must rely on manufacturer claims that often lack reliable scientific evidence.
Scientific Consensus on Oral Ingestion Safety
Scientific understanding suggests orally ingested colloidal gold poses a relatively low acute toxicity risk, primarily due to poor absorption in the gut. Research indicates that only an extremely small fraction of orally administered gold nanoparticles is absorbed into the bloodstream, sometimes less than 2%. The majority of ingested nanoparticles pass through the digestive tract and are excreted.
The small amount of gold that is absorbed is primarily eliminated through urine. While most gold is cleared relatively quickly, studies show slight accumulation can occur in organs, such as the kidney, liver, and spleen, depending on particle size and coating.
Although low-dose colloidal gold may not pose an immediate acute toxicity threat, the long-term effects of chronic, daily consumption remain largely unstudied. The lack of comprehensive long-term data on bioaccumulation and its consequences, combined with the absence of demonstrated health benefits, leads to a cautious scientific stance. Therefore, while CG is not immediately toxic, its consumption is generally unwarranted given the lack of proven efficacy.