Smaller newborns more likely to develop ADHD, mental health problems

DUBLIN, Ireland — Researchers have discovered a new way to identify people at risk for future mental health conditions: birth weight. In their latest study, scientists from Ireland found that babies born with normal birth weights have fewer mental health and behavioral problems during childhood and adolescence than those who are underweight.

“We have known for many years that low birth weight and premature birth is linked with higher risk of mental illness in the child,” explains senior author Mary Cannon, a professor of psychiatric epidemiology and youth mental health at RCSI, in a university release. “What this study shows is that even small deviations from the typical birth weight might also be relevant.”

The findings come from birth weight data on thousands of children in Ireland. Researchers followed up with these children through childhood and early adolescence. The Growing Up in Ireland study made this possible, as it is an ongoing review of children born between 1997 and 1998.

For every 2.2 pounds (one kilogram) below the average birth weight of 7 pounds-11 ounces babies were, there were more instances of mental health problems throughout childhood and adolescence. Moreover, those with low birth weights continued to have this problem after childhood, from ages nine to 17. The most commonly reported problems included inattention, impulsivity and hyperactivity, and behaviors associated with ADHD.

For every 2.2-pound drop below the average birth weight, there was a two-percent increase in ADHD-like behaviors. The team notes, however, that this increased risk was not enough to give children a formal ADHD diagnosis. Lower birth weight also displayed a connection to emotional and social problems, especially in teens. These issues were more likely to bring people closer to a diagnosis of depression or anxiety.

“This relationship between birth weight and child mental health persists even after accounting for factors that could influence both birth weight and mental health, like gender, socioeconomic factors and parental history of mental illness,” notes lead author Niamh Dooley, a PhD student at RCSI University of Medicine and Health Sciences. “The effect of birth weight on later mental health is likely small, but it might interact with other risks like genetics and childhood stress, and have implications for understanding the origins of mental health and ill-health.”

The results suggest expecting mothers should follow good perinatal care and closely monitor their health during pregnancy to increase the chances of a healthy birth weight. For example, a separate study from the group found that birth weight and showing signs of ADHD have a connection to drug behavior during pregnancy — whether it’s smoking, alcohol, or non-prescription drug use.

For children already born with low birth weights, the study authors say they would benefit from early interventions focusing on managing mental health symptoms and potentially preventing more severe illness in the future.

The study is published in the journal European Child & Adolescent Psychiatry.

About the Author

Jocelyn Solis-Moreira

Jocelyn is a New York-based science journalist whose work has appeared in Discover Magazine, Health, and Live Science, among other publications. She holds a Master’s of Science in Psychology with a concentration in behavioral neuroscience and a Bachelor’s of Science in integrative neuroscience from Binghamton University. Jocelyn has reported on several medical and science topics ranging from coronavirus news to the latest findings in women’s health.

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