How dad's smoking reduces son's fertility?
Fertility Male fertility Smoking

How dad's smoking reduces son's fertility?

Samantha Levell
Samantha Levell

In 10 seconds? Fathers’ smoking can seriously affect their sons’ fertility, a study has found, but the good news is: quitting before conception can help avoid the problem.

What’s the discovery exactly? Researchers have found that men whose fathers smoked during conception had around 51% less total sperm count and 41% less sperm concentration than men with non-smoking fathers.

I know about smoking and pregnancy, so what’s new here? Previous studies predominantly linked pregnant mothers’ smoking to decreased sperm counts in sons. This Swedish study revealed that smoking fathers can also directly affect their son’s fertility to a dramatic extent, independently of the mothers.

OK, and how exactly do fathers affect their sons? Tobacco smoke contains substances that cause mutations and damage in DNA. These mutations can be passed onto the offspring, resulting in reduced sperm quality in male children. Researchers found that the number of mutations in smoking fathers’ children was much higher than in the sons of non-smoking dads. One thing to keep in mind: the study sample was small, 104 men, so further research with larger cohorts is needed to reproduce the findings.

The total sperm count in men of mothers that did not smoke (cotinine < 15ng/mL), divided in 17 men of whom the father smoked at the time of the pregnancy, and 57 men of whom the father did not. Dark lines in the middle of the boxes are median values.Source: Axelsson, Sabra, Rylander, et al, 2018.
The total sperm count in men of mothers that did not smoke (cotinine < 15ng/mL), divided in 17 men of whom the father smoked at the time of the pregnancy, and 57 men of whom the father did not. Dark lines in the middle of the boxes are median values.Source: Axelsson, Sabra, Rylander, et al, 2018.

What else is passed on with damaged DNA? Good question! According to new research, nicotine-affected, altered DNA can cause behavioral changes down the generations. Researchers have discovered this by feeding male mice with nicotine and detecting learning difficulties in their 3rd generation offspring.

How did they discover the father’s role? Researchers used a combination of surveys for the fathers and blood tests for the mothers to isolate the effects caused by dads. Using blood samples taken from the mothers during pregnancy, they could measure the level of cotinine, an ‘end product’ of the breakdown of nicotine. This helped verify if the mother smoked herself, or was exposed to secondhand smoke from the father.

Gosh, have I damaged my future son if I smoked before? Not necessarily. Avoiding tobacco during pregnancy is certainly a good way to protect our children from the effects of smoking. Additionally, the damage caused by tobacco to the dad’s DNA can be reversed. In other words, if the future father stops smoking, his sperm will gradually become healthier, so he won’t ‘gift’ reduced fertility to his son.

Hang on, is it only the sons of dads who are affected? Good question! The short answer is no. Researchers have found that smoking is behind 1.3 million 'aneuploid' pregnancies per generation (i.e. pregnancies with an abnormal chromosomal count - read more on why is this bad in this Digest). In other words, the evidence says that the harmful effects of smoking on fertility are not just limited to the parents but their children can inherit them too.


'Behave, Dad!' Smoking fathers cause mutations

Most newly occurring mutations come from the father. Children of fathers who smoke can have up to four times as many mutations in a certain region of their genome than children of non-smoking fathers.

These mutations can be linked to several diseases, such as autism, birth defects, diabetes, and obesity. Additionally, the new study established that the father's smoking was also linked to a shorter reproductive lifespan in daughters.

But here are some good news: it takes about three months for sperm to mature, which means that men who stop smoking at least three months before conception will have much healthier sperm with a greater chance of fertilizing an egg, and creating a healthy baby.

Samantha has distilled 8 research papers to save you 28 hours of reading time. This is an updated version of an earlier Digest.



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