Antioxidants may help improve male fertility, early research suggests.
A review of existing data found, compared with controls, a couple was more likely to have a pregnancy or live birth if the man took certain vitamins or other antioxidants.
Researchers from The Cochrane Library looked at trials of more than 1,000 couples at fertility clinics where most of the men had low sperm counts.
A UK expert said more research was needed.
Male subfertility - where a man struggles to get his partner pregnant - affects one in 12 UK men.
Some clinics advocate the use of antioxidants, which are natural and synthetic chemicals, including certain vitamins and minerals.
The use of antioxidants is based on the theory that free radicals - highly reactive atoms with an odd number of electrons - can cause damage to the DNA in sperm, which is vital for creating an embryo.
The result could be lowered sperm counts and an impaired ability to fertilise eggs.
Dr Allan Pacey, Senior Lecturer in Andrology at the University of Sheffield gave a cautious welcome to the research, which he said was "encouraging".
However, he said it was important to note that antioxidant therapy would be unlikely to increase the numbers of sperm men produce and could not therefore help with all cases of male infertility.
He added that it was an area of ongoing interest:
"To date, the research has been controversial with some studies showing evidence of benefit and others showing no improvement.
"This meta analysis seems to suggest that there is an increased chance of pregnancy in the partners of men who took antioxidant therapy, although the numbers are still small. Clearly more research is needed."
The review focused on 34 controlled trials involving couples undergoing assisted reproductive techniques such as in vitro fertilisation and sperm injections.
Most men in the trials had low sperm counts or low sperm motility.
The trials also explored the use of many different types of oral antioxidants, including vitamin E, L-carnitine, zinc and magnesium.
Lead researcher, Marian Showell from the University of Auckland in New Zealand said taking an oral antioxidant supplement may increase a couple's chance of conceiving when undergoing fertility treatment:
"When trying to conceive as part of an assisted reproductive program, it may be advisable to encourage men to take oral antioxidant supplements to improve their partners' chances of becoming pregnant."
She acknowledged though that evidence is still limited and that more work needs to be done.
Dr Pacey said that men with fertility problems should always consult their doctor:
"Men who think antioxidant therapy may help them should consult their doctor and only take the therapy if they are advised to do so."