Smoking may not just be bad for men. It may be bad for their children and grandchildren. Matt Cardy/Getty Images

New research suggests that smoking by fathers may cause changes in their sperm that lead to cognitive deficits in their children — and even their grandchildren.

The study, which looked at male mice fed nicotine in their drinking water, was published Tuesday in the journal PLOS Biology by Pradeep Bhide of Florida State University in Tallahassee and colleagues.

“Nicotine can have direct harmful effects on the male who is using it, and as our study now suggests, also have adverse effects on his offspring’s cognitive function,” Bhide said in an e-mail.

The researchers said that when the male mice were bred with female mice that had never been exposed to nicotine, their offpsring displayed hyperactivity, attention deficit, and cognitive inflexibility.

The effect even extended to a second generation: when the female children (but not the male children) were bred with males that had not been exposed to nicotine, their offspring still displayed significant deficits in cognitive flexibility, researchers said.

Studies have already shown that mothers shouldn’t smoke, exposing themselves to nicotine and other smoke components, because it is a signficant risk factor for behavioral disorders, including attention deficit hyperactivity disorder in multiple generations of descendants, researchers said.

“Until now, much attention had been focused on the effects of maternal nicotine exposure on their children. Not much had been known about the effects of paternal smoking on their children and grandchildren. Our study shows that paternal nicotine exposure can be deleterious for the offspring in multiple generations,” he said.

The researchers suggested that the effect could be due to epigenetic changes in key genes in the father’s sperm. They said they found that multiple genes in the nicotine-exposed males’ spermatozoa had been epigenetically modified, including one that is critical for brain development.

Bhide said it’s not clear how long the nicotine effect would persist in a male’s sperm.

“It is possible that some of the epigenetic changes caused by nicotine in the sperm DNA are temporary, and go away with time, which would mean that children conceived after a certain period of abstinence from nicotine use might not be affected,” Bhide said in an e-mail.

“Other epigenetic changes may be permanent, and may result in deleterious effects on the offspring. More studies are needed” to know the answer, he said.

Bhide said the study raised questions not only about what current smokers are doing to future generations, but what past generations of smokers have done to people alive today.