Pollution, smoking, varicocele, diabetes, testicular tumours and age can have the greatest effect on the quality of sperm cells, according to the largest meta-analysis to date. Based on nearly 27,000 studies, Semmelweis University specialists have identified the most dangerous factors that can damage the genetic material of sperm. Men’s reproductive capacity has drastically decreased in recent decades, and the research draws attention to the importance of prevention.

Amongst others, the researchers scrutinised men’s age. They found that over the age of 50, the integrity of the sperm DNA begins to deteriorate significantly.

In a study recently published in the journal Reproductive Biology and Endocrinology, Semmelweis University researchers from Budapest, Hungary, examined the factors that can significantly affect the fragmentation of sperm’s genetic material.

“The so-called DNA fragmentation analysis is currently the only evidence-based test for determining the functionality of sperm cells. It examines their DNA content, namely the proportion of intact or fragmented genetic material in the sperm. The more fragmented the DNA, the less the sperm’s ability to fertilise; also, it can increase the risk of miscarriage”, explains Dr. Zsolt Kopa, head of the Andrology Centre at the Department of Urology at Semmelweis University.

The scientists searched three international databases for previously published studies. They found 26,901 articles, of which 190 were eligible for their meta-analysis. All were published between 2003 and 2021, mostly in Europe, the U.S. and Asia, fewer in Africa and Australia, and data of thousands of men treated in infertility clinics were compared.

Some results surprised even the researchers.

“Based on previous research, we expected that the quality of sperm cells starts to deteriorate significantly after age 40, but our meta-analysis suggests that this age could be much higher.

We identified a notable increase in DNA fragmentation from age 50 when it jumped by an average of 12.58% compared to younger men.

But, of course, this is not to say that it’s worth waiting to start a family as other important parameters can also deteriorate with advancing age,” says Dr. Anett Szabó, a Ph.D. student and first author of the Semmelweis publication.

It has only been assumed, as well, that lifestyle can influence sperm quality. In the current study, the researchers demonstrated that smoking could increase DNA fragmentation by an average of 9.19% compared to non-smokers. 

Alcohol consumption and body weight, on the other hand, did not have a clinically significant role in the fragmentation of genetic material in the recent meta-analysis, but the tendency that more alcohol and higher body weight lead to more considerable fragmentation was detectable. 

Some specialists also recommend relatively frequent ejaculation (every 2-3 days) to patients; however, the current analysis suggests that the length of the abstinence period is not relevant to DNA fragmentation.

On the other hand, pollution had a detrimental effect on sperm quality. In two reviewed studies, a region of Italy (Land of Fires) was examined where the environmental pollution is exceptionally high due to illegally transported toxic waste. Another publication compared data from steel factory workers. A third study examined police officers helping the traffic at a busy junction.

The meta-analysis found that various factors, such as air pollution, the exposure to pesticides or insecticides (work-related or other), increased sperm DNA fragmentation by an average of 9.68%.

The role of certain health problems in sperm dysfunction is well known. Varicocele (dilation of the veins in the spermatic cord), for example, increases sperm DNA fragmentation by an average of 13.62%. Reduced glucose tolerance can also affect it to a similar extent. According to the current meta-analysis, tumours can also significantly increase DNA fragmentation (by 11.3 %).

Certain infections, such as Chlamydia and HPV, did not impair sperm quality, but bacterial or other sexually transmitted diseases showed increased DNA fragmentation (8.98% and 5.54%).

“In recent years, there has been an increasing demand to measure men’s fertility with functional, objective parameters, in addition to the classical quantitative and qualitative characteristics. DNA fragmentation can be of outstanding importance, and the test got officially included in the international guidelines in 2021. However, there are still no official standards on the values of infertility and fertility. In clinical practice, we use only consensus values. Generally, a fragmentation below 25% can be considered optimal; above this, the chance of spontaneous conception decreases. Beyond 50%, the success rate of IVF is also lower,” explains Dr. Zsolt Kopa.

The World Health Organization defines infertility as when a couple does not achieve pregnancy within one year after unprotected, regular sexual intercourse. According to previous research, the concentration and quantity of men’s sperm have decreased drastically in recent years.

According to previous studies, the fertility rate in Western developed countries is declining: one in six couples suffer from infertility problems. There are multiple causes, and approximately 50% can be attributed to men. Although the rate of unexplained infertility has decreased significantly in recent decades, in 30% of cases, the causes are still not found.

A high rate of DNA fragmentation may be one explanation. It is, therefore, worthwhile to optimise lifestyle factors even before trying for a child – the experts warn. For example, quitting smoking, engaging in regular physical activity, or eating more healthily could be a good start.

“Amongst others, we also identified risk factors that lifestyle changes can prevent. Men can reduce the risk of DNA damage with a healthier lifestyle, which can be a more successful and cost-effective approach to child planning in the long term,” adds Dr. Anett Szabó.

The Hungarian researchers aim to continue their work by analysing the impact of various intervention options on men’s fertility.

Photo: Balint Barta – Semmelweis University; Cover photo: iStock – rez-art