It’s Monday morning and I have just the thing to wake you up. It’s a three word combo: antioxidants + subfertility + evidence. Yes I was interested too. We so often hear claims for health benefits of antioxidant supplements (cranberry capsules, green tea, bee spit and so on and so on) and there’s a huge market for them amongst women who are trying to get pregnant, particularly for the increasing number who are having difficulty conceiving, now thought to be around a quarter of couples. Many of the antioxidant supplements taken in the hope of improving fertility are unregulated and readily available to buy. But is there any evidence that antioxidants benefit woman trying to conceive and do we know if there are risks attached?
Today a new Cochrane review has been published which sought to answer these questions. It includes data from 28 randomized controlled trials involving over 3,500 women. A variety of antioxidants were used and were compared with each other or with a placebo (sugar pill), with no treatment or with folic acid. The outcomes of interest were live birth, pregnancy rates and adverse (bad) events.
What did they find?
- Antioxidants were not associated with an increased live birth rate
- Antioxidants were not associated with an increased pregnancy rate
- Some evidence (3 trials, 276 women) that pentoxifylline was associated with an increased pregnancy rate, though not in women with endometriosis, but future trials may change this result. Also, pentoxifylline is a medicine with actions beyond the antioxidant properties
- Limited evidence on adverse effects (14 trials) found no difference between antioxidant groups and control groups
How good was the evidence?
Not good! The overall quality of the evidence was ‘very low’ to ‘low’ because of poor reporting, the number of small studies, big differences between trials and high risk of bias in studies. Variation in the types of antioxidants taken meant it wasn’t possible to assess whether one was better than another. Only four trials reported the main outcome – live birth; two more said they would but only reported pregnancy. None of the trial protocols were available so we don’t know if they reported on all the outcomes they expected to.
So what’s the bottom line, for those thinking about trying it?
Lead researcher, Marian Showell, who works in Obstetrics and Gynaecology at the University of Aukland, New Zealand, put it plainly:
“There is no evidence in this review that suggests taking an antioxidant is beneficial for women who are trying to conceive.”
No good evidence that it helps or harms, in fact. More, better trials are needed and it is crucial that they state up front that they are going to report on live birth, pregnancy and adverse effects. An earlier Cochrane review looked at antioxidants for male subfertility and found they were associated with an increase in live birth rates, but this was based on three small trials and needs to be confirmed in larger trials. It’s important to note that these trials involved men seeking fertility treatment at clinics. You can read a helpful explanation of this review from NHS Choices here.
Sorry not to have better news, but antioxidants are costly, in terms of both hope and hard cash invested in them, and it’s important to know what’s the evidence behind the hype.
Showell MG, Brown J, Clarke J, Hart RJ. Antioxidants for female subfertility. Cochrane Database of Systematic Reviews 2013, Issue 7. Art. No.: CD007807. DOI: 10.1002/14651858.CD007807.pub2.
Showell MG, Brown J, Yazdani A, Stankiewicz MT, Hart RJ. Antioxidants for male subfertility. Cochrane Database of Systematic Reviews 2011, Issue 1. Art. No.: CD007411. DOI: 10.1002/14651858.CD007411.pub2.
Cochrane summary and podcast http://summaries.cochrane.org/CD007411/antioxidants-for-male-subfertility
Algra A. Factor Xa inhibitors: a step forward in the treatment of atrial fibrillation? [editorial]. Cochrane Database of Systematic Reviews 2013;8:ED000064. dx.doi.org/10.1002/14651858.ED000064