I never exactly planned to become an “attachment parent,” co-sleeping with my babies, holding them and wearing them 24/7 like an extra appendage, and nursing on demand even after they started walking and talking. It’s just what happened. It feels right to me, and it works for my family.

Research shows that this kind of closeness has positive implications for small humans, decreasing their stress levels and promoting healthy brain development. A new study from the University of British Columbia and BC Children’s Hospital Research Institute reveals that physical contact between infants and their caregivers can even affect children at the molecular level – an impact that’s detectable four years later.

By studying DNA methylation patterns, scientists from UBC and BC Children’s Hospital found that children who had received less physical contact from their caregivers and had been more distressed as infants had a molecular profile that was underdeveloped for their age, suggesting that these children were behind, biologically.

What this means for their later development and health has yet to be determined, as this study was the first of its kind to show how touch in infancy could have such far-reaching implications for our DNA. But experts like Michael Kobor, a Professor in the UBC Department of Medical Genetics and leader of “Healthy Starts” at BC Children’s Hospital Research Institute, suspect that this lag may indicate an “inability to thrive.”

The findings published last month in the journal Development and Psychopathology expand upon similar research conducted on rodents. The study involved 94 healthy children in British Columbia and relied on detailed reporting from their caregivers.

Parents of five-week-old babies were asked to document their infants’ behavior in a journal, noting how they slept, fussed, cried, and fed. They were also asked to record the duration of daily parenting that involved physical contact. Then, when the children were about four-and-a-half years old, researchers sampled their DNA by swabbing the inside of their cheeks.

This is where things get complicated, unless Biology is your jam. Otherwise, you can skip ahead. According to UBC:

“The team examined a biochemical modification called DNA methylation, in which some parts of the chromosome are tagged with small molecules made of carbon and hydrogen. These molecules act as ‘dimmer switches’ that help to control how active each gene is, and thus affect how cells function. The extent of methylation, and where on the DNA it specifically happens, can be influenced by external conditions, especially in childhood. These epigenetic patterns also change in predictable ways as we age.”

Researchers discovered consistent methylation differences at five different DNA sites between children who’d had much physical contact as infants and those who hadn’t. Two of the sites fall within genes that play a part in the immune system and in metabolic functioning. But the consequences of those differences on child development and health are not yet known.

What these results tell us is that children who experienced little physical contact and high levels of distress as infants had a lower than expected “epigenetic age” relative to their actual age. The children who experienced higher distress and received comparatively little contact had an epigenetic age that was lower than would be expected, given their actual age. This kind of incongruity can be associated with poor health, according to recent research.

Lead author and postdoctoral fellow Sarah Moore explains that she and her colleagues plan to follow up to find out whether the “biological immaturity” observed in the children could mean wide-ranging consequences for their health, particularly their psychological development. “If further research confirms this initial finding,” she says, “it will underscore the importance of providing physical contact, especially for distressed infants.”

We should all stay tuned. In the meantime, what Moore and her team did uncover is that bodily contact in infancy can literally leave traces on our genes, suggesting that touch plays an even more significant and complex role in human development than we thought.

“This is the first study to show in humans that the simple act of touching, early in life, has deeply-rooted and potentially lifelong consequences on genetic expression,” the authors explain.

If I had a dollar for every time I’ve been given side-eye for my decisions to bed-share with my babies or pick them up every time they cry, I could go on a serious shopping spree. I know the time I spend snuggled up with them is priceless. According to this new research, it’s also leaving a lasting imprint on their DNA.