Causes of male infertility examined

“A man's fertility depends more on his mother's lifestyle than his own,” according to the Daily Mail. The newspaper says a “large-scale review” of factors that affect the production of sperm has concluded that how a woman looks after herself in pregnancy could affect her unborn baby’s ability to father a child in adulthood.

This research is a review of selected studies that assessed the effects of maternal factors and factors in adulthood on sperm count in males. The review supports the theory that some lifestyle factors, including smoking and obesity during pregnancy, can affect the sperm count of male offspring when they reach adulthood.

The methodology of this type of review means it is difficult to know whether all the relevant evidence has been considered in this round up. However, the findings do lend support to the advice given to pregnant women and adults, to maintain a healthy lifestyle, diet and weight and to avoid smoking.

Where did the story come from?

The study was carried out by Dr Richard Sharpe from the MRC Human Reproductive Sciences Unit at Queen’s Medical Research Institute in Edinburgh. The research was funded in part by the UK Medical Research Council and by the European Union. The review was published in the peer-reviewed medical journal Philosophical Transactions of The Royal Society .

News sources have generally covered this research in a balanced way. However, they have selectively focused on the impact of smoking, while they could equally have discussed the range of other factors under consideration here, such as obesity.

What kind of research was this?

This was a narrative review of factors affecting spermatogenesis (production of sperm), in which the author specifically discussed environmental and lifestyle effects on sperm production, including the foetal determinants, the effects of lifestyle during adulthood and the effects of environmental chemicals.

What did the research involve?

The author of this review precedes his discussion with an introduction that describes the high prevalence of couple infertility, which he says affects one in seven couples. He says these cases of fertility problems are often mainly because of ‘male factor’ infertility. According to previous research, the prevalence of an abnormally low sperm count in young men is as high as 15-20%. Other research suggests that only a small percentage of the sperm in some men's semen can be classified as ‘normal’. These points suggest that human spermatogenesis is very different to that of animals, and the author of this review set out to discuss processes and factors that could affect spermatogenesis in the human male.

What were the basic results?

Dr Sharpe discusses a number of animal and human studies that contribute to this assessment of spermatogenesis in human males. He outlines what is known about foetal development and the differentiation of the germ cells in developing testes. He also discusses the findings of some studies (animal and human studies) that have examined the effects of exposures such as female obesity and environmental chemicals including exhaust fumes, combustion products and pesticides.

Importantly, he notes that, with respect to the effects of environmental chemicals on masculinisation, the evidence is by no means definitive and that “the evidence linking such exposures in perinatal life to low sperm counts in adulthood is … non-existent”. He says there is a notable exception to this: exposure of pregnant women to dioxin, a highly toxic by-product of combustion. Following the Sevaso incident (an industrial accident that happened in 1976 when a chemical plant in Italy released material into the air, exposing a large residential population to dioxin) lower sperm counts were later observed in males who had been exposed as foetuses. Animal studies also suggest that exposure to diesel exhaust fumes reduces sperm production in adulthood.

The author then says that several large studies have noted “substantial reductions in sperm counts” in men whose mothers smoked heavily in pregnancy, although only a minority of these studies found a significant effect on the quality of sperm that was produced. He cites four publications (that are not reviewed in this article) on the subject. According to Sharpe, aside from these, no other studies have identified a specific lifestyle or environmental exposure during pregnancy that subsequently affects sperm counts in human male offspring during adulthood.

In a later discussion of the factors affecting spermatogenesis in adulthood, the author reports that “there is little evidence” that either smoking or alcohol has a major impact on spermatogenesis, although smoking may have a small negative effect. The author also discusses the effect of other factors during adulthood on sperm production, including scrotal heating, obesity, occupational exposures and environmental exposures.

How did the researchers interpret the results?

In concluding remarks, the author notes that the high prevalence of low sperm counts in young men across Europe is a cause for concern, and suggests that sperm production is subnormal either because of factors affecting adult men or because of development problems in the womb.

He says that, despite the practical difficulties in identifying exactly what factors are responsible, the implications for fertility and population renewal in the West “provide the strongest possible incentive to strengthen research in this area”.

Conclusion

This narrative review has discussed the evidence concerning spermatogenesis in adult males by considering research on both the factors that affect the male foetus and those that affect adult males. It should be noted that this research was a narrative review, and as such it is difficult to know exactly how the author has selected the discussed studies and whether there has been a full assessment of all the relevant evidence pertaining to this topic.

The newspapers have specifically chosen to focus on this author’s discussion of the effect of maternal smoking (the review discusses studies that suggest that men whose mothers smoke heavily have substantially reduced sperm counts, lowered by up to 40%). The results also suggest that there is only limited evidence that smoking as an adult male negatively affects sperm count.

However, the newspapers could equally have chosen to report on obesity, which was also considered by this review. The author says that one preliminary study suggests that a high maternal BMI negatively affects semen quality in resulting sons when they reach adulthood. Importantly, being obese as an adult is a risk factor for reduced sperm count and reduced sperm motility.

This review highlights a number of important factors and discusses their potential effects on male sperm counts. Its findings emphasise the importance of pregnant women avoiding smoking and maintaining a healthy lifestyle and weight, which are pieces of well-established general health advice for both males and females.