Researchers from the University of Western Australia and the University of Auckland, New Zealand, have shown that there is currently no evidence that taking supplemental antioxidants improves the chance of pregnancy. The results were reported in a review of fertility clinical trials published this week in The Cochrane Library.

The ever-growing global vitamin and supplement industry is massive, currently estimated to be worth around US$68 billion (2010). Many women turn to supplements as a potential treatment for infertility, antioxidants in particular.

Exposure to stress, pollution and drugs can increase the production of free radicals - a type of oxygen molecules toxic for cells. Natural antioxidants produced by our bodies combat free radicals to prevent cell damage, but there is no clear evidence that taking antioxidant supplements has any such effect.

Research shows that free radicals are linked to certain types of infertility in women, such as endometriosis or polycystic ovarian syndrome for instance.

Over the past two decades, the number of couples seeking fertility treatment has been on the rise. On average, around one in four couples planning to have a baby will have problems conceiving. Fertility issues can be caused by a number of factors, but in many cases the specific cause for infertility remains unclear. Couples who find themselves in this difficult position often turn to assisted reproductive techniques, such as in vitro fertilization.

Many women will also take antioxidants supplements to help improve their chances of conception. However, there is limited evidence that nutritional supplements improve fertility, and little attention has been paid to the potential harmful effects of taking unregulated antioxidants.

But do antioxidant supplements really improve a woman's chances of getting pregnant?

In their new study, Dr. Marian Showell and colleagues reviewed data from 28 clinical trials on 3548 women seeking to improve their fertility by taking one or more antioxidants. Some of the most common antioxidants used included vitamins A, C and E, and folic acid. The conclusion? "Antioxidants were not associated with an increased live birth rate or clinical pregnancy rate", the authors wrote in the study. Women taking antioxidant supplements didn't have a better chance at conceiving than women not taking any supplements.

There was also no evidence from the clinical trials to suggest that taking antioxidants may have adverse effects, such as miscarriage or ectopic pregnancy, but the data was limited, the authors noted.

The authors stressed that the overall quality of the antioxidant clinical trials was low, and further studies would be needed to make the case for antioxidants.

"Consumer perception is that antioxidant therapy is not associated with harm and is associated only with benefit. It is important to establish whether or not this therapy does improve fertility and whether it is associated with any harm", the authors wrote in the study.