For much of the last century, research into childhood mental and physical health focused heavily on mothers. Social scientists often linked long-term problems in children to difficult early relationships with their mothers, who were sometimes described as distant, overbearing or emotionally inconsistent. Fathers, by contrast, were frequently treated as secondary figures, if they were studied at all.
New research suggests that approach may have missed a crucial part of the picture.
A study by researchers at Pennsylvania State University has found that a father’s behaviour in a child’s first year of life may play a decisive role in shaping the child’s physical health years later. In some cases, the influence of fathers appeared stronger than that of mothers.
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The findings, published in the academic journal Health Psychology, are based on a long-term study of 292 families across the United States. The researchers observed interactions between parents and their infants at 10 months old, followed up when the children were aged two, and then again at seven.
Rather than looking at parents in isolation, the team focused on three-way interactions: how mothers, fathers and infants behaved together. These sessions were filmed during short periods of play and later analysed for parental sensitivity, emotional warmth and how well parents worked together as a team.
The patterns that emerged were striking.
Fathers who were less attentive to their babies at 10 months were more likely to struggle with co-parenting. Instead of supporting the mother-child relationship, some fathers withdrew from interactions or competed with mothers for the child’s attention. When the children reached the age of seven, those family dynamics appeared to show up in the children’s bodies.
Blood tests revealed that children whose fathers had been less engaged were more likely to have higher levels of inflammation and poorer markers of metabolic health, including raised blood sugar. These indicators, such as C-reactive protein and glycated haemoglobin, are associated with an increased risk of heart disease and diabetes later in life.
By contrast, the researchers found no comparable link between mothers’ early parenting behaviour and these physical health markers.
Alp Aytuglu, a postdoctoral scholar at Penn State and one of the study’s authors, said the result surprised the research team. “We expected that family dynamics as a whole would matter,” he said. “But in this case, it was fathers’ behaviour that stood out.”
The study builds on a large body of evidence showing that children raised in stressful environments face higher risks of obesity, diabetes and premature death as adults. Chronic stress can be traced through biological signals such as inflammation and blood glucose, which rise when the body is repeatedly placed on high alert.
What makes this research different is its focus on fathers. According to Greg Miller, a psychology professor at Northwestern University, fathers have often been overlooked simply because studies usually involve only one parent, typically the mother. That, he said, reflects a long-standing assumption in North American psychology about who matters most in child development.
The Penn State team offers two possible explanations for their findings. One is what they call the “father vulnerability hypothesis”: the idea that fathers may be particularly sensitive to relationship strain and that their negative reactions can ripple through the family. Another is that because mothers often spend more one-on-one time with young children, a father’s behaviour may have a stronger impact when the whole family is together.
The researchers also point to policy implications. More generous parental leave for fathers, they argue, could give men more time to build secure relationships with their children in the earliest months, reducing stress for the entire family.
Experts caution against overinterpreting the results. Sarah Schoppe-Sullivan of Ohio State University noted that the study shows correlation, not cause, and that genetics or unmeasured family factors could play a role. The families involved were also mostly white and middle class, limiting how widely the findings can be applied.
Even so, she described the results as impressive, given how difficult it is to track family behaviour and health outcomes over many years.
The message, researchers stress, is not that mothers matter less. Rather, it is that fathers matter more than previously recognised, not just emotionally or socially, but in ways that may shape their children’s health for decades to come.
