June 25, 2019

expert reaction to abstract on preconceptional and prenatal exposure to paternal smoking and semen quality of adult sons

Research presented in an abstract at the 35th annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) shows that paternal smoking is associated with lower total sperm counts and sperm concentrations. 

Dr Rod Mitchell, Consultant Paediatric Endocrinologist & Group Leader, MRC Centre for Reproductive Health, University of Edinburgh, said:

“The association between ‘in-utero’ exposures and future reproductive health of the male offspring are well established in animal models, supported by association studies in humans.

“Ruling out alternative explanations (e.g. alcohol consumption or BMI) for associations [between smoking and sperm count in the adult sons] is a particular strength of the study design.

“The reported reduction in sperm count (46%) when the mother smokes would be expected to have a direct effect on fertility in some sons. However, the reported reduction in sperm count if the father smoked was much more modest and importantly was non-significant, meaning it could simply be due to chance alone.

“If such an association between paternal smoking and sperm count in sons were proven, this could represent direct effects of smoking on the fathers sperm, or alternatively it may be a result of in-utero effects of exposure to passive smoking on fetal testicular development. However, the study does not explore a mechanism for this reported association.

“Given that major health risks of smoking are well recognised, this study may indicate yet another reason to consider modification of this lifestyle factor.

“Importantly, whilst the study appears to have been conducted in a robust fashion, the study requires scientific peer-review and publication before definitive conclusions can be drawn.

Prof Richard Sharpe, MRC Centre for Reproductive Health, University of Edinburgh, and member of the Society for Endocrinology:

“We have known for some time that smoking by mums in pregnancy is associated with up to a 40% decrease in sperm count in resulting sons when they become adults, based on 4 independent studies; and of course, maternal smoking is associated with numerous other long-term adverse health effects for the resulting babies. What the latest Danish study shows for the first time, apart from confirming these 4 previous studies with regard to maternal smoking ‘effects on sperm count’, is that smoking by the father during the pregnancy that gave rise to his son, is also associated with a non- significant but slightly adverse effect on his son’s sperm count, albeit of smaller magnitude than that found if the mother smoked. This may be yet another brick in the wall showing the harmful effects of passive smoking. The study appears sound and utilises the superb medical databases available in Denmark. Whilst this is an association study, and therefore does not prove that paternal and/or maternal smoking during pregnancy causes a decrease in sperm count in resulting sons, the consistency of the findings (for maternal smoking) in now 5 independent studies makes it more likely that this is cause and effect. Assuming this to be the case, we still do not know the mechanism, although top of the list would be that smoke chemical exposure reduces the rate at which the Sertoli cells in the foetal testes increase in number, as it is the final number of Sertoli cells that determines the ceiling of sperm production (and thus sperm count) in adulthood.”

Prof Allan Pacey, Professor of Andrology, University of Sheffield, said:

This is an interesting study which highlights a small but potential link between a man’s sperm quality and the lifestyle of his parents. We now know that many aspects of adult health, including fertility, are established very early in life before we are born. Therefore, to date, most investigations into this area have tended to focus on the health and lifestyle of the mother. For example, previous studies have shown that the sperm quality of men whose mothers smoked during pregnancy are significantly lower than those whose mothers didn’t. However, very little attention has been focussed on the lifestyle of the father (presumably because he isn’t the once carrying the pregnancy). In this study, a small but non-significant effect is seen on the sperm quality of son’s born to partnerships where the father smoked but the mother didn’t. The authors conclude that this could be because the fathers smoking causing genetic changes in his sperm that were then passed onto his son. This may be true. But I do wonder if it simply a case of “passive smoking” by the mother as presumably the fathers and mothers of these males shared a common household? However, regardless of the precise biological effect, the data does serve to illustrate the need for both future fathers and mothers to be as healthy as possible, both before and during a pregnancy.

The abstract ‘Prenatal exposure to paternal smoking and semen quality in the adult offspring’ by Dr Sandra Sogaard Tottenborg et al. was presented at the 35th annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) on Tuesday 25 June. 

Declared interests

Prof Richard Sharpe: No conflicts of interest.

None others received.