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Healthy or toxic? The conflicting images of antioxidants

By Annie-Rose Harrison-Dunn+

11-Feb-2015
Last updated on 16-Feb-2015 at 09:25 GMT2015-02-16T09:25:38Z

There's a thin line between toxic and healthy, say researchers looking at the shifting perceptions of antioxidants
There's a thin line between toxic and healthy, say researchers looking at the shifting perceptions of antioxidants

Benefit-risk ratios must be established for each antioxidant separately, considering risk groups and dosage, according to researchers reviewing polarised perceptions of vitamin E and beta-carotene.

The researchers from Maastricht University, the Netherlands Food and Consumer Product Safety Authority (NVWA) and the Dutch National Institute for Public Health and the Environment (RIVM) said in recent years there had been two opposing images of antioxidants: Totally healthy or totally toxic.

In an attempt to find a more moderate view they looked at two separate antioxidants with opposing health portrayals, the ‘poisonous’ β-carotene and the ‘wholesome’ vitamin E. They then focused on their respective roles in inducing Benzo(a)pyrene diolepoxide (BPDE)-DNA adducts. A DNA adduct is a piece of DNA bonded to a cancer-causing chemical, while BPDE is a polycyclic aromatic hydrocarbon associated with burning material like wood and linked to cancer.  

They found that both antioxidants promoted DNA adduct formation and therefore displayed a similar type of toxicity, regardless of their very different public perception.

“Despite its reputation of being healthy, vitamin E has a dark side that is astonishingly similar to that of β-carotene,” the researchers wrote in the journal Redox Biology.

They said benefit-risk ratios could help tackle this polarised narrative.

The concept of oxidative stress only emerged in the second half of the 20th century. Since then hyperbolic advice has directed people to take high quantities of antioxidant foods and supplements in order to harness their ability to protect against reactive oxygen species (ROS). Yet more recently evidence emerged that such high quantities may hold mortal risks.

“The dilemma that still needs to be solved is: What are antioxidants in the end, healthy or toxic?” they said.  

Measuring up the risks

Looking at the two antioxidant’s influence on BPDE-DNA adducts, they pointed to a study from the 90s that found β-carotene increased the incidence of lung cancer in smokers by inhibiting the body's protective activity. They said this appeared to be counter-intuitive since smoking caused oxidative damage, so it was assumed antioxidants would help counter this.

For the supposedly ‘wholesome’ vitamin E similar risks were detected, with one study suggesting it could promote tumour activity in mice exposed to cancer-inducing compounds.  

Additional toxic effects for people using coal tar ointments in medicated shampoo and soaps were also discussed, which in combination induced polycyclic aromatic hydrocarbon (PHA)-DNA adducts in the skin. PHA refers to a group of carcinogenic environmental pollutants.

This, coupled with the benefits of the nutrients, showed there was a thin line between toxic and healthy”.

Concluding the report, they said: Antioxidants are consumed to improve health and not because they are not toxic. In our appreciation on antioxidants priority is given to the risks and this needs to be corrected. The priority should be to identify groups that are likely to benefit.”

Greater knowledge of the molecular mechanisms around the risks as well as identification of which groups were at risk was now needed. They added that supplementation of antioxidants from a natural source did not guaranty safety.

Source: Redox Biology

Vol. 4, April 2015, P. 272–278, doi:10.1016/j.redox.2014.12.017

“The shifting perception on antioxidants: The case of vitamin E and β-carotene”

Authors: M.F. Vrolijk, A. Opperhuizen, E.H.J.M. Jansen, R.W. Godschalk, F.J. Van Schooten, A. Bast and G.R.M.M. Haenen

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