Beware of antioxidants

The review, carried out at Brighton and Sussex Medical School (BSMS), run jointly by the universities of Brighton and Sussex, are warning: that the evidence for oxidative stress causing many diseases are weak.

The lay press and thousands of nutritional products warn of oxygen radicals or oxidative stress and recommend taking so-called antioxidants to prevent or treat illness, ensure healthy aging or “boost the immune system”.

But Professor Pietro Ghezzi at BSMS and Professor Harald Schmidt at the University of Maastricht have analysed the evidence behind this and concluded that there are no demonstrated benefits to taking these supplements. 

Their findings have been published in the British Journal of Pharmacology: The oxidative stress theory of disease: levels of evidence and epistemological aspects.

Professor Pietro Ghezzi

Life depends on oxygen to produce energy for our body. The oxygen has also the potential to generate so-called oxygen radicals, which may cause “oxidative stress” and be toxic. Markers of oxidative stress have been correlated with cardiovascular disease, cancer, and diabetes. Because of these associations, antioxidant supplements are taken by millions of people.

Professor Ghezzi, Chair in Experimental Medicine at BSMS, said: “A lot of people assume antioxidants will only do them good, but they can actually be doing harm. Our review shows that to be safe, you should only take if you really have a diagnosed vitamin deficiency”.

“Randomised clinical trials testing antioxidants have not shown conclusive evidence for any benefit. On the contrary, some antioxidants may have a harmful effect. This is due to the fact that oxygen radicals are not only triggers of disease, but have many essential functions in our body, such as the immune defence and hormone synthesis. Thus antioxidants will always interfere with both healthy and potential disease-triggering oxygen molecules. The net effect is therefore zero or apparently even negative.”

Professor Schmidt said: “Nevertheless, oxidative stress could be important in some conditions and in a small proportion of patients. However it can be managed in a totally different manner, with classical drugs targeted only at those sources of oxygen molecules that are triggers of disease and leaving the healthy ones alone."