Smoking Raises Risk of ADHD in Children by Changing Sperm, Mice Study Suggests

Fathers who smoke may increase the risk that their children and grandchildren will develop mental disorders, scientists found after a study on mice.

Using nicotine could change the genes in a man's sperm and affect how his children develop, researchers at Florida State University in Tallahassee concluded.

To test their hypothesis that nicotine could negatively affect a man's offspring, the team fed male mice water containing the addictive substance. They then bred the males with females who had not taken any nicotine.

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Mice who were exposed to nicotine had "significant" changes in the DNA of their sperm. And their offspring were born with abnormalities in the neurotransmitters dopamine and noradrenaline, and their receptors, which are believed to play a key role in the development of behavioral disorders.

The offspring of mice who were given nicotine were more likely to be hyperactive, have attention deficits and struggle with cognitive flexibility, the researchers found. In humans, these symptoms are often associated with attention deficit hyperactivity disorder (ADHD) and autism. What's more, struggling with cognitive flexibility was passed on to the rodents' grandchildren.

The study was published in the journal Plos Biology. It offers a new perspective on how the consequences of using nicotine could be inherited, the authors wrote. The discussion often focuses on a mother's smoking habits—even though more men than women smoke, they said.

In the past, studies have linked smoking during pregnancy with a heightened risk of disorders such as ADHD, oppositional defiant disorder and conduct disorder—but the mechanisms that underlie these associations are unclear, according to the Centers for Disease Control and Prevention.

While mice and humans are both mammals and so share a similar physiology, results from research using rodents does not necessarily translate to humans. But the study's authors said it was difficult to isolate the effects of smoking on humans as so many environmental and genetic factors muddy the results. Using rodents in a laboratory setting therefore provides a clean slate for scientists to investigate nicotine use.

The authors of the study did not immediately respond to requests for comment. Study author Pradeep Bhide, a professor of neuroscience and director of the Center for Brain Repair at Florida State University College of Medicine, explained in a statement that past research had linked nicotine and cigarette smoking to epigenetic changes in sperm, or the mechanism by which genes are switched on and off.

"The fact that men smoke more than women makes the effects in males especially important from a public health perspective," he said.

"Our findings underscore the need for more research on the effects of smoking by the father, rather than just the mother, on the health of their children."

Professor Peter Hajek, director of the Tobacco Dependence Research Unit, Queen Mary University of London, was skeptical about whether smoking would have the same effect in humans as seen in mice.

"Twelve eight- to 10-week old mice were forced to absorb what for them are huge doses of nicotine for the next 12 weeks and this seems to have severely damaged their sperm and their offspring," he said. "Such studies rarely translate to human smokers."

Susanna Roberts, a postdoctoral research associate at the Institute of Psychiatry Psychology and Neuroscience, King's College London, pointed out that studies suggesting that inherited epigenetic marks, particularly those those linked to environmental exposures such as nicotine use, have sparked skepticism in recent years.

She said that although this paper focused on a small set of genes, she praised the authors for using mutliple forms of biological and behavioral data to corroborate their findings.

"Despite the interesting results, it is difficult to extrapolate the importance of these effects in humans, where the causal pathways to behavior and influences on biology are immeasurably more complex," she said.

Further research needs to be conducted using human subjects to replicate the findings "before the implications are fully understood," she added.