Sperm count found to be 50% lower in sons of fathers who smoke

Sperm count found to be 50% lower in sons of fathers who smoke
© iStock/Julia Simina, Olga Zarytska

Research found that independent of nicotine exposure from mothers, sons of fathers who smoke had half as much sperm count compared to non-smoking fathers.

Many studies have continuously linked maternal smoking during pregnancy with lower sperm count in male offspring. Now, according to Lund University, Sweden, it has been discovered that independent of nicotine exposure from the mother, men of fathers who smoke at the time of pregnancy had half as many sperm as those with non-smoking fathers.

Fathers who smoke had 41% lower sperm count

In order to control the variables, the researchers adjusted the mother’s own exposure to nicotine, socioeconomic factors, and the sons’ own smoking, and found that men with fathers who smoked had a 41% lower sperm concentration and 51% fewer sperm than men with non-smoking fathers. The research team at Lund University is the first to have reported this finding.

Jonatan Axelsson, specialist physician in occupational and environmental medicine explains further regarding the study: “I was very surprised that, regardless of the mother’s level of exposure to nicotine, the sperm count of the men whose fathers smoked was so much lower.”

Cotinine is a biomarker and also a metabolite from nicotine which can be measured in the blood. By measuring the level of cotinine, researchers could see whether an individual smoked or whether they had been exposed to passive smoking.

Many previous studies have shown that it is harmful to the foetus if the mother smokes but, in this study, the link between the father’s smoking habit and the son’s sperm count has become much clearer.

What are the underling mechanisms to low sperm count?

Axelsson cannot explain why this is the case and thinks that more research is required to understand the underlying mechanisms. However, on the other hand, he explained how similar studies have also shown links between smoking fathers and various health outcomes in children, such as malformations.

“Unlike the maternal ovum, the father’s gametes divide continuously throughout life and mutations often occur at the precise moment of cell division. We know that tobacco smoke contains many substances that cause mutations so one can imagine that, at the time of conception, the gametes have undergone mutations and thereby pass on genes that result in reduced sperm quality in the male offspring.”

Most newly occurring mutations, de novo mutations, come via the father and there are also links between the father’s age and a number of complex diseases.

Smoking is linked to DNA damage in sperm and researchers have found that smokers have more breaks in the DNA strand. Moreover, children of fathers who smoke have been reported to have up to four times as many mutations in a specific repetitive part of the DNA as children of non-smoking fathers.

“We know there is a link between sperm count and chances of pregnancy, so that could affect the possibility for these men to have children in future.” Concludes Axelsson.

“The father’s smoking is also linked to a shorter reproductive lifespan in daughters, so the notion that everything depends on whether the mother smokes or not doesn’t seem convincing. Future research could perhaps move us closer to a causal link.”

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