Male fertility: sperm and stress

How is male fertility faring?
02 March 2021

Interview with 

Bill Colledge, Cambridge University


Sperm surrounding an egg cell.


We've heard about female fertility, let's turn now to male fertility. Katie Haylor spoke with Bill Colledge, a reproductive physiologist from Cambridge University. Firstly, Katie asked Bill if there's any evidence that the Covid-19 pandemic could be impacting male fertility...

Bill - Well, it's an interesting question. There was a study that was published just a few weeks ago where they were looking at indicators of male fertility, such as sperm numbers and the motility of the sperm, after individuals had a COVID infection. And they found that there was an impairment in the sperm quality even three months after these individuals had got over the initial COVID infection. So that would indicate that if you have a COVID infection it can alter the quality of the sperm. But I would like to reiterate here that you probably would see the same thing with other viral infections as well, such as influenza. There is data to suggest that sperm quality goes down after an influenza, and it's probably more related to the body fighting off a virus in general rather than just COVID. So that's often associated with a high fever and we know that a high fever can impair sperm quality.

Katie - So I guess knowing how long that lasts must be quite a crucial question, right?

Bill - It's a very crucial question. The study only looked after three months, they didn't go any further out than that. So we don't really know how long it would take for the sperm quality to get back to normal. They also didn't relate it to fertility, they were simply looking at sperm numbers and motility. And of course, fertility is a different aspect - is it possible for those individuals to still conceive, even though they have impaired sperm?

Katie - What about stress and anxiety? Catherine mentioned it as some sort of indirect influence. Is there evidence to suggest that stress and anxiety can impact male sperm?

Bill - There is evidence that high stress can alter the male reproductive axes. So if you're under a lot of stress and you have this stress hormone cortisol being produced in the body, that will tend to suppress the reproductive axes, which could lower the amount of testosterone in the body which you need in order to make sperm. So under those conditions you could actually see a reduction in the number of sperm being made - perhaps not so much a change in the quality of the sperm, but just in the quantity.

Katie - Catherine was mentioning the sorts of factors that are understood to influence female fertility outside of the context of the pandemic. Broadly, does that list look the same when we're talking about male fertility?

Bill - It's pretty similar actually. Obesity is a very important contributory factor in male fertility, mainly because individuals that are obese tend to have lower testosterone levels. And as I've said, you need testosterone to get your body to make the sperm, so everyone that has an increase in 9 kilograms has a 10% reduction in fertility. So there's a direct correlation there between body weight and obesity and fertility. There are other factors that also affect male fertility - smoking, I think was mentioned as affecting females, but it will also affect male fertility. There are substances within cigarette smoke that are not very good for sperm production - there are toxic substances like cadmium and lead, and they will certainly interfere with sperm production. And then of course the various toxins that you might find within the environment. Sperm formation is very, very sensitive to these substances, and if you get them in your body it can compromise the sperm formation.

Katie - And what about air pollution? Have there been studies done looking at air pollution and sperm?

Bill - There have been studies done, but as Catherine said, the problem with most of these studies is they tend to just be correlations and they often tend to be done in small groups. The best way to look at this is to look at all of the studies together and to do what is called a meta-analysis to try and put all of the publications into one, and to do the statistics on that to look at whether air pollution can affect male fertility. There has been a meta-analysis done in 2015, and they did show that air pollution does correlate with reduced sperm motility, but it didn't seem to affect overall fertility levels. So again, you've got to be careful talking about a reduction in sperm numbers and how that might affect fertility.

Katie - Now we've heard a number of reports in recent years about sperm quality and quantity being on the decline. Is this the case? What evidence is there to support this? Is it seen across the globe or is this a UK problem?

Bill - So there are several studies over the last 20 years that have clearly indicated a decline in the number of sperm. And again, if you look at all those studies together and you do a meta-analysis, there was a very good meta-analysis done in 1992, and what they found was that indeed there is a reduction in the number of sperm being produced and the amount. So I think in 1940, the average sperm count was 113 million per ml, but by 1990 it had dropped to 66 million per mil. So there has been a significant reduction in the number of sperm. Now this tends to only affect the Western developed countries. Studies have been done in Asia, and they have been done in China. There is some evidence to suggest similar reduction in sperm numbers, but less pronounced. So it does seem to be mainly in the developing Western countries.

Katie - And in just the last sentence, do we actually know why this is happening?

Bill - It's multifactorial, but probably obesity and weight gain will be a big component in this.


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