Are you worth your weight in gold? Sort of.

Studies have revealed that gold is present in the human body. But don't get too excited, it's only there in trace amounts: about 0.2 milligrams in an average 70-kilogram person. These are detectable in tissues and fluids such as the liver, kidneys, blood plasma, and even in hair and nails. To put the quantities into perspective, our bodies also contain, on average: 43 kilograms of oxygen, 16 kilograms of carbon, 1 kilogram of calcium, a little over 4 grams of iron, and 60 milligrams of aluminium. In short, the concentrations of gold in the human body are minuscule, yet pervasive within our biological framework.

Past and present uses

While scientists continue to speculate on its role in biological processes, gold likely isn't in our bodies by mistake. It appears to support cellular communication, which is critical for nerve function and brain activity, as well as the health and maintenance of our joints. This would explain why gold-containing compounds, sometimes referred to as gold salts, have been used in the past to treat inflammatory conditions such as rheumatoid arthritis.

The ancient cultures of China, India and Egypt, which revered the metal for its purported purification and longevity properties, were known to have incorporated it into medicinal or alchemical preparations. Meanwhile, traditional Chinese medicine used to turn the metal into powders and foils to treat skin infections, palpitations, seizures, and mercury poisoning – perhaps Napoléon could have used some?

Thanks to advances in nanotechnology, potential uses of gold nanoparticles in imaging are being explored for cancer therapy. The inert and highly conductive properties of gold could allow for the delivery of drugs directly to tumours, minimising the risk of damage to healthy cells. Researchers are also investigating their potential for the prevention and treatment of neurodegenerative diseases, such as Alzheimer's disease, multiple sclerosis and Parkinson's disease.

In vivo and in vitro risks of exposure

It is also important to remember that some forms of gold exposure have downsides.

Outside the human body, such exposure can occur through jewellery or dental devices and may induce allergic reactions. Allergic contact dermatitis, for example, can cause redness and itching. Although scientists have found that, given the many potential routes of exposure to the metal, its toxic risks were low.

Now, within a living organism – a mouse - researchers have previously observed that high concentrations of gold nanoparticles can lead to decreases in body weight, red blood cells and hematocrit. Administering these nanoparticles orally and directly into the peritoneal cavity showed the highest toxicity, and tail vein injection the lowest, indicating that the latter is more suitable for use in radiotherapy, photothermal therapy and other diagnostic procedures.

From drug delivery to imaging to regenerative medicine, the potential of gold compounds is non-negligible. But more research will be needed to fully understand its biological functions and potential therapeutic implications.