Which antioxidants have been proven to be beneficial?

Vitamin E has the strongest and most consistent evidence base of all antioxidants. Children with higher blood levels of vitamin E develop wheezing or asthma less often: this is the only association that a large review of 32 meta-analyses classified as consistent. Vitamin E supplements may also improve arterial function and reduce inflammatory markers in the blood, but that evidence is preliminary.

For women with reduced fertility, antioxidant supplements show a modest improvement in the chance of pregnancy. In a large review of 63 studies involving 7,760 women, that chance rose from approximately 19% to 25 to 30%; whether more children were actually born alive remains uncertain. Men with fertility problems who took antioxidants saw their chance of a live birth potentially rise from 16% to 17 to 27%, but this effect disappeared once the less reliable studies were excluded. Mild gastrointestinal complaints were slightly more common in men: the risk rose from approximately 2% to 2 to 7%. Always discuss antioxidants for fertility problems with your doctor.

In children with difficult-to-treat epilepsy, a combination of vitamin C and E produced a far greater reduction in seizures on top of standard medication: a 95% reduction compared with 35% in the control group. This is a small study of 88 children, so firm conclusions would be premature.

Omega-3, pycnogenol and vitamin D appear to be the most promising supplements for ADHD symptoms in children, but the underlying studies are methodologically weak. Research on antioxidants in brain tumours has not progressed beyond animal and laboratory studies, so no clinical conclusions can be drawn here.

Dietary vitamin E is associated with a lower occurrence of cervical and oesophageal cancer, but these are associations; it has not been proven that vitamin E prevents those cancers.