Studies have repeatedly linked maternal smoking during pregnancy, with reduced sperm counts in male offspring. A team of researchers at the University of Lund in Sweden found that regardless of mother's exposure to nicotine, men whose parents smoked at the time of pregnancy had half the sperm count of non-smokers.
The study was conducted in 104 Swedish men aged 17 to 20. Once the researchers adjusted their own exposure to nicotine, socioeconomic factors, and child smoking, men with parents who smoked had a 41% lower sperm concentration and 51% fewer sperm than men with non-smoker parents. The research team at Lund University is the first to report this finding.
"I was very surprised that regardless of the mother's level of exposure to nicotine, the sperm count of men whose parents smoked was much lower," says Jonatan Axelsson, a medical specialist in occupational and environmental medicine.
The cotinine biomarker is a metabolite of nicotine that can be measured in the blood. By measuring the level of cotinine, researchers can see if their parents smoke or have been exposed to secondhand smoke. Many previous studies have shown that it is harmful to the fetus if the mother smokes, but in this study the link between the father's smoking habit and the child's sperm count is even clearer.
Jonatan Axelsson can not explain why this happens and thinks more research is needed to understand the underlying mechanisms. On the other hand, he explains, similar studies have also shown links between smoking parents and various health outcomes in children, such as malformations.
"Unlike the maternal ovum, the father's gametes continuously divide throughout life, and mutations often occur at the very moment of cell division. We know that tobacco smoke contains many mutating substances, so we can imagine that at the moment from conception, gametes mutated and thus transmit genes that result in reduced sperm quality in male offspring. "
Most mutations that occur recently (known as de novo mutations) come through the father and there are also links between the father's age and a number of complex diseases. In addition, the researchers noted that smoking is linked to DNA damage in the sperm and that smokers have more breaks in the DNA chain. Children of parents who smoke have reported having up to four times more mutations in a certain repetitive part of the DNA than the children of non-smoking parents.
"We know there is a link between sperm count and the chances of pregnancy, which could affect the possibility of these men having children in the future." The father's smoking is also linked to a shorter reproductive life in daughters, so the notion that everything depends on whether the mother smokes or not, does not seem convincing. Future research may perhaps bring us closer to a causal link, "concludes Jonatan Axelsson.
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