While research has repeatedly linked maternal smoking during pregnancy with reduced sperm count in male children, a new research has shown that men whose fathers smoked at the time of pregnancy also had a 50 percent lower count of sperm than those with non-smoking fathers.
The findings showed that, independently of nicotine exposure from the mother, socio-economic factors and their own smoking, men with fathers who smoked had a 41 percent lower sperm concentration and 51 percent fewer sperm counts than those with non-smoking fathers.
"I was very surprised that, regardless of the mother's level of exposure to nicotine, the sperm count of men whose fathers were smoked was so much lower," said Jonatan Axelsson, specialist physician at Lund University in Sweden.
"We know there is a link between sperm counts and chances of pregnancy, so it could affect the possibility for these men to have children in the future.
"The father's smoking is also associated with a shorter reproductive lifespan in daughters, so the notion that everything depends on whether the mother smokes or does not seems convincing," he added.
However, the research has not determined the underlying mechanisms behind this. But, similar studies have shown links between smoking fathers and various health outcomes in children, such as malformations, Axelsson noted.
It could be because most new occurring mutations come through the father and there are also links between father's age and a number of complex diseases, researchers said in a paper published in the journal PLOS ONE.
In addition, researchers have observed that smoking is linked to DNA damage in sperm and that smokers have more breaks in the DNA strand.
Children of fathers who smoke have been reported to have up to four times as many mutations in a certain repetitive part of DNA as children of non-smoking fathers.
"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 thus pass on genes that result in reduced sperm quality in male offspring," Axelsson said.
The study was conducted on 104 Swedish men aged between 17 and 20 years.