Substance abuse not only causes hazardous health issues to users, but can also affect the health of future generations. A new study suggests that alcohol and drug abuse in parents can cause intellectual disability in children, even if only one of the parent had the issue.

"Maternal alcohol use is a known risk factor for intellectual disability, but less is known about the importance of maternal and paternal substance use disorder and risk of intellectual disability in offspring," researchers from Karolinska Institutet explained. The findings of the study were published in the journal eClinicalMedicine.

For the study, the team used Swedish registries that had records of two million babies born between 1978 and 2002 and their parents.

Around 1.2% of babies born to parents without any alcohol/substance abuse disorder showed intellectual disability, while 3% of babies who had at least one parent with the issue showed symptoms.

The offspring had higher intellectual disability when the parents had alcohol-related problems during pregnancy. The risk was five times when the mother used alcohol during pregnancy, while it was three times when the father had alcohol use disorder.

The risk of intellectual disability in children was more than two times higher when the parent was diagnosed before or during pregnancy, irrespective of which parent had the diagnosis.

"Preventative measures, such as educating healthcare professionals and public health recommendations, have focused for decades on mothers with alcohol-related problems. Our findings highlight the importance of also directing such measures towards fathers with different types of substance use disorder," Lotfi Khemiri, a lead author of the study, said in a news release.

Although it is not known how substance abuse affects kids' brains, researchers believe it has to do something with genetic and environmental factors.

"Since it was an observational study, we can draw no conclusions about the underlying mechanism, but we suspect that both genetic and environmental factors, including harmful effects of substance abuse on fetal development, may play a part," Khemiri said. "We hope that the results will contribute to the preventative efforts, as well as to the improved diagnosis of children with an intellectual disability and to timely intervention directed both to the child as well as parents in need of substance use disorder treatment."