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Antioxidants, Reactive Oxygen Species and your Fertility

Sperm have a pretty tough time. They begin life in the testes, where – after a gruelling 74 days on the production line – they wind their way through coiled tubes to reach the prostate gland.

It’s from here that sperm will be ejaculated during sex. They’re catapulted at a monumental speed into a hostile environment which seeks to attack and thwart them at every opportunity. The vagina.

If the determined travellers can navigate these harsh conditions, their chances of fertilising an egg are still pretty slim. A sperm must battle it out against millions of his competitors on a marathon journey.

Even though the distance between the sperm and the egg is only about 10cm, the tiny sperm’s whip-like tail can only propel it at about 3mm per hour, meaning the journey can take forever!

And if that isn’t enough for the little swimmers to worry about, during their difficult life they have another problem to contend with. Reactive oxygen species (ROS).

What are ‘antioxidants’ and ‘ROS’?

ROS are very volatile molecules which contain oxygen. Normally, natural processes in the testes lead to the production of a small amount of ROS in seminal fluid (the fluid in which sperm are nurtured). These small amounts of ROS are needed for normal sperm function.

But if the amount of ROS is left unchecked, they can become bad news – causing something known as ‘oxidative stress’ – which damages cells.

Luckily, molecules known as antioxidants are at hand to help stop ROS causing any damage. Antioxidants can be found in the testes (as well as other places), and they balance out the effects of ROS by preventing any cells being exposed to oxidative stress.

But sometimes the balance of ROS and antioxidants can get knocked so that the level of ROS is too high for antioxidants to control. And this can spell trouble for sperm, as it means they are put under oxidative stress.

The ROS can now wreak havoc on sperm, damaging sperm DNA and the membrane surrounding sperm cells and reducing the ability of sperm to move spontaneously. This can have devastating effects on a man’s fertility. If sperm want to stand a chance at fertilising an egg; they need to be in mint condition!

It’s no wonder that oxidative stress in the testes is now being blamed as one of the fundamental causes of fertility problems in men.

What can be done to stop ROS negatively affecting male fertility?

Sperm are sensitive little things and the slightest inconvenience can make their one big goal in life unattainable. In fact, in 50% of couples facing fertility issues, defective sperm can be pin-pointed at the root of their problems.

When trying to conceive, a man needs to give his sperm the best possible chances at succeeding.

Could we introduce synthetic antioxidants in men to circumnavigate the bad effects that ROS have?

This is the question that has been long debated amongst scientists.

Fortunately, a review published in the Reproductive BioMedicine Online journal may once and for all give us a definitive answer to the question.

Photo credit: Carsten Schertzer / Photo / CC BY

The review analysed the results of 17 other studies (which in total contained 1665 men). They had all looked at the effect that oral antioxidant supplements had on sperm quality and partner pregnancy rate in men facing fertility issues.

The oral antioxidants taken by men in the studies included vitamins C and E, zinc, selenium, folate, carnitine and carotenoids and, on average, antioxidants were taken for 18 weeks.

The review showed that 14 out of the 17 (82%) of the studies showed an improvement in either sperm quality or pregnancy rate after the men had taken antioxidants.

It was crucial that the antioxidants were taken for an extended period of time. In two out of the three studies that found no improvements after antioxidants, the oral supplements were only taken for eight and nine weeks. The researchers speculated that the men in these studies probably weren’t taking the antioxidants long enough to warrant any effect!

Looking at the positive results a bit closer shows us that six out of the ten studies looking at pregnancy rate showed an increase in pregnancy after the men in the study had been taking antioxidants.

Nine of the ten studies looked at antioxidant effect in couples trying to conceive naturally and the remaining study looked at antioxidant effect in men undergoing intra-cytoplasmic sperm injection (ICSI), which is a type of in-vitro fertilisation (IVF) treatment.

In both cases, pregnancy rate was higher where men had been taking antioxidants.

What’s more, 12 out of the 16 (75%) studies looking at sperm quality found an improvement in at least one aspect of sperm quality after antioxidant treatment.

So overall, it seems antioxidant supplements can reduce the damage caused by ROS in men trying to conceive. And this is good news for sperm quality and pregnancy rates!

And observational studies have shown, even without taking supplements, men can still get the beneficial effect of antioxidants by changing their diet. Here’s a list of some the most antioxidant rich foods.

Antioxidants and assisted reproduction treatments

In nearly all of the studies looked at in the review mentioned above, the researchers looked the effect of antioxidants on pregnancy rates in couples trying to conceive naturally.

But, currently, about 15% of couples face fertility issues and they are increasingly turning to assisted reproduction treatments to help them conceive.


And – as with natural conception – sperm need to be in top condition to give assisted reproduction treatments the best chance at success. This is especially important since sperm quality is one of the main factors that determines their likelihood of working.

So it’s just as important that we know how ROS and antioxidants might influence a couple’s chances of conceiving when they’re undergoing an assisted reproduction treatment.

A study published last month appears to shed a bit more light on this. The study shows us how the little swimmers react to ROS and antioxidants when they’re used to fertilise a woman’s eggs in a lab during treatments such as IVF and ICSI.

Sperm used for IVF and ICSI are separated from the seminal fluid. When they leave this fluid behind, they’re losing out on the protective effect that the natural antioxidants in the fluid provide.

What’s worse, some of the processes that are carried out during the handling and preparation of sperm for assisted reproduction techniques (such as freezing and thawing of sperm) can lead to the production of ROS.

So the sperm are getting even more exposure to ROS than usual, but there are no antioxidants there to protect them!

It’s for this reason that the researchers decided to test if adding an antioxidant – in the form of zinc – to sperm during assisted reproduction techniques could help to prevent oxidative stress occurring.

Sperm were collected from 20 healthy men and then mixed with either just a ROS, just zinc, or a ROS and zinc. Some sperm samples were also mixed with a neutral liquid to check that it was not anything else besides the ROS and antioxidants affecting the sperm. This is known as a control treatment.

The researchers then looked at their samples to check what effect each mixture had produced in the sperm. They did this by looking at the quality of sperm characteristics such as sperm movement, viability and DNA.

As expected, mixing sperm with just a ROS led to lower quality sperm than the control group.

But when sperm were mixed with a ROS and zinc (the antioxidant), the researchers found that all the sperm characteristics they looked at were improved in comparison to the sperm that had been mixed with just a ROS.

However, mixing sperm with zinc alone appeared to be bad for sperm quality. So it’s important that antioxidants are only added in the presence of ROS during assisted reproduction treatments.

But, fortunately for couples seeking help with conceiving, this study shows us that on the whole, zinc can help to protect sperm from ROS when fertilisation is carried out by scientists in a lab.

So it appears that men trying to conceive and scientists performing assisted reproduction treatments can offer a helping hand to make sperm’s lives a bit easier. Just by adding a touch of antioxidants!

After all, every little helps when it can seem like the whole world is against a sperm on his mammoth journey to find and fertilise an egg.

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