DR MICHAEL MOSLEY: Men should ditch tight underpants after male fertility and birth rates plummet

Throughout my adult life, I’ve always been a big fan of finding out what’s going on in my body.

Over the years I’ve tried out a wide range of tests — from standard ones for measuring my blood sugar levels and cholesterol, to those that claim to predict my risk of dementia (low, apparently) and even athletic ability (my genes suggest I would make a better powerlifter than a sprinter).

So when I read that some supermarkets are now selling a home test for male fertility, I was tempted.

For though I’m now 66 years old with four children, and have absolutely no intention of having more kids, I was curious to see if I still could.

When I mentioned the test (which measures sperm count) to my wife, Clare, she thought it was a terrible idea, so I decided not to. But such tests exist because one in seven British couples struggles to conceive — and in half the cases, the problem is with the man.

Studies have shown that the testes can overheat when wearing tight underwear and this can contribute to a low sperm count

This situation could soon worsen, as a recent major study revealed an alarming decline in sperm counts.

The research, which was published in the journal Human Reproduction Update last November, was based on data collated from 53 countries and found that men from North and South America, Asia, Africa and Europe had all experienced a 50 per cent or greater decline in sperm counts in the past 46 years.

What’s more disturbing is that the rate of decline has doubled since 2000. One of the study authors, Professor Hagai Levine, of Hadassah Braun School of Public Health in Jerusalem, said we had ‘a serious problem on our hands that, if not mitigated, could threaten humankind’s survival’.

Why does declining fertility matter? Not so long ago many people were worried that a rapidly growing population would overwhelm the planet, with warnings of mass starvation and global wars as people fought for scarce resources.

Just last year, the United Nations predicted that the number of people living on Earth would hit 9.7 billion by the middle of this century and would continue to rise.

But the number of babies being born has slowed so dramatically that Earth4All, a group of leading environmental science and economic institutions, now predicts that the global population will peak at less than nine billion and then start to fall, rapidly.

Apart from the personal sadness for those who want to conceive but can’t, a drop in birth rates leads to an ageing population — and a smaller workforce (which also means fewer people to look after that ageing population) and less tax income for governments.

I’m now 66 years old with four children, and have absolutely no intention of having more kids, I was curious to see if I still could, writes Dr Michael Mosley (pictured)

Obviously, there are a number of factors at play — the cost of childcare and soaring house prices mean many couples are deciding to opt for one child, or two at most. But the evidence suggests falling fertility and falling sperm counts are also playing their part.

Professor Levine points to rising rates of obesity, combined with what he calls ‘chemicals in the environment’ for damaging men and women’s reproductive health.

These chemicals include PFAs (per-and polyfluoroalkyl substances) which are also known as ‘forever chemicals’, because they don’t readily break down and hang around in the environment.

PFAs are found in drinking water as well as in a wide range of consumer products such as food packaging and the stain-resistant coatings on carpets and furniture.

As I’ve written before, they accumulate in our bodies and have been linked with an increased risk of heart disease, as well as kidney and testicular cancers. But more recently we’ve learned that PFAs can also cross the placenta and affect the growing foetus.

A study of 864 young men in Denmark, published last October, found that those whose mothers had been exposed to higher levels of PFAs early in pregnancy (measured by looking at stored blood samples) produced significantly less sperm and more of those sperm were abnormal.

Another study, published in March, showed that women of child-bearing age with higher levels of PFAs in their blood were 40 per cent less likely to get pregnant and have a baby over the course of a year than those with lower levels.

This is not definitive proof that PFAs cause infertility, but the advice from the lead researcher, Dr Nathan Cohen, a public health expert at the Icahn School of Medicine at Mount Sinai in New York, is to minimise exposure to them if you can.

Which is easier said than done, because they are everywhere.

Filtering your tap water may help, while eating less junk food is also a good idea, as the packaging it comes in often contains PFAs — research published in October 2019 by the University of Massachusetts found that people who ate more of their meals from fast-food take-aways had higher levels of PFAs in their blood than those who didn’t.

Non-stick pans are also a source of PFAs, so discard them if they get badly scratched and don’t use them to fry at high heat.

As I mentioned earlier, you can now buy home-testing kits that can, apparently, detect with 98 per cent accuracy if your sperm count in normal — though they won’t tell you if they’re healthy.

If your count is low and you are hoping to have children, then it may be worth losing weight and switching to boxer shorts — as studies have shown that the testes can overheat when wearing tight underwear and this can contribute to a low sperm count.

And do, of course, see your GP for further advice.