The researchers focused on men who were sub-fertile and found that those who took antioxidants were more than four times as likely to get their partners pregnant than sub fertile men who did not take the supplements.
The New Zealand team stops short of saying that antioxidants actually improve fertility, however. More research is needed to be sure, they write in The Cochrane Library.
Sub fertility affects one in 20 men and is responsible for half of delayed conceptions. Up to 80% of cases are thought to be due to the effects of oxidative stress on sperm cells, lowering both their numbers and their quality.
"Oral supplementation with antioxidants may go some way to improve a couple's chance of conception," said lead researcher Dr Marian Showell of the University of Auckland.
To see if the research to date backs up that theory, Dr Showell and her colleagues reviewed 34 studies that involved nearly 3,000 couples undergoing fertility treatments. Each study investigated the potential role of one or more antioxidants.
Based on 96 pregnancies among 964 couples in 15 of the studies (follow-up three to 24 months), the researchers found that antioxidant use by the male partner significantly increased the likelihood of conception (odds ratio 4.18, p < .001). There were 82 pregnancies in 515 couples in the antioxidant group (16%) and 14 in 449 couples (3%) in the control group.
Three trials compared rates of live births during a period of six to 24 months: 18/116 (16%) vs 2/98 (2%), respectively (OR 4.85, p < .001).
However, "The findings of increased live birth rates with antioxidants are based on a total of only 20 births - a relatively small number," Dr Mark Sigman of Brown University, in Providence, R.I., who was not involved in the review, told Reuters Health in an e-mail.
Dr Sigman, whose research found no improvement in semen quality with the antioxidant carnitine, was cautious about making too much of the review's results.
Result failed to determine effectiveness
The included studies did not use the same types or numbers of antioxidants, he added. As a result, the researchers could not determine the effectiveness of individual supplements.
Both Drs Sigman and Showell cautioned that couples should not count on antioxidants to overcome their fertility challenges. Even if certain supplements prove effective, further research is needed to determine which couples could reap the specific benefits.
"It is unrealistic to think one treatment will be good for most couples," noted Dr Sigman.
"There is no evidence that antioxidants cause harm," he added. "But since we also don't know which antioxidants or doses are beneficial - and none have FDA approval for infertility - consumers are left with purchasing these based on very limited data."(Reuters Health/ January 2011)