Concerns have been raised over the long-term use of nutritional supplements containing chromium, after an Australian research team found the supplement is partially converted into a carcinogenic form when it enters human cells.

Chromium is a trace mineral found primarily in two forms: a range of chromium(III) forms are sold as nutritional supplements, while hexavalent chromium(VI) is its ‘carcinogenic cousin’, gaining notoriety from the book and 2000 movie, Erin Brockovich, which linked a cluster of illnesses to its presence in drinking water. Controversy remains over whether the dietary form of chromium is essential, with an increasing body of evidence indicating it is not safe.

In the study, researchers from The University of Sydney and UNSW treated cells with chromium(III) before creating a map of every chemical element contained inside the cell using an intense synchrotron X-Ray beam at the Advanced Photon Source (APS) in Chicago. The team accessed the APS through the Federal Government’s Australian Synchrotron Research Program, which provided researchers with synchrotron access prior to the Australian Synchrotron opening in 2007.

Dr Lindsay Wu, from UNSW’s School of Medical Sciences and who originated the research while at The University of Sydney, said the high energy synchrotron beam allowed the team to identify and classify chromium spots throughout the cell.

‘The powerful X-Ray enabled us to determine whether the spots were chromium(III) or a combination of chromium(III), chromium(V) and chromium(VI).

‘The health hazards associated with exposure to chromium are dependent on its oxidation state – we were able to show oxidation of chromium inside the cell does occur, meaning it loses electrons and transforms into a carcinogenic forms, which no-one had been able to do in a biological sample before.’

Supplements containing chromium are consumed for the purported treatment of metabolic disorders, such as insulin resistance and type 2 diabetes, but chromium’s mechanism of action in the body is not well understood.

These supplements are also commonly used for weight loss and body building with some containing up to 500 micrograms per tablet, above the 200 micrograms estimated as a safe and adequate daily dietary intake for adults by the US National Academy of Sciences. Australia’s current National Health and Medical Research Council Nutrient Reference Values, which are currently under review, recommend 25-35 micrograms of chromium daily as an adequate intake for adults.

Research lead Professor Peter Lay from the University of Sydney’s School of Chemistry said with the latency period for chromium(VI)-related cancers often greater than 20 years, the finding raises concerns over the possible cancer-causing qualities of chromium compounds and the risks of taking chromium nutritional supplements long term or in high doses.

‘With questionable evidence over the effectiveness of chromium as a dietary supplement, these findings should make people think twice about taking supplements containing large doses of chromium.

‘However additional epidemiological research is needed to ascertain whether chromium supplements significantly alter cancer risk, since long-term laboratory experiments have not been conducted under the conditions of high oxidative stress (which promotes chromium(III) oxidation) associated with diabetes.’

The researchers said the findings are very unlikely to apply to trace amounts of chromium(III) found in food.

Experiments were also conducted at the former Australian National Beamline Facility at the Photon Factory in Japan, operated by the Australian Synchrotron, which helped clarify the nature of the chromium(V) and chromium(VI) species formed in the cells, both of which can cause cancer.

The research, published in the prestigious chemistry journal, Angewandte Chemie was also supported by the Australian Research Council.

Originally published by UNSW Media.

Media coverage:

 ‘Popular chromium supplements linked to carcinogens’, Sydney Morning Herald, Monday 11 January 2016.