How often you hold your baby actually affects their DNA, study finds

A loving mother’s caress is more than simple comfort to an infant. Scientists have known for decades that touch is critically important for a child’s healthy development, according to an article in the journal Pediatric Child Health.

But now a new study shows that the amount a baby is touched can leave lasting, measurable effects — not just on behavior or growth, but all the way down to the molecular level of the DNA. Those changes, the scientists speculate, could have negative effects on the way the child grows and develops.

For the study, scientists at the University of British Columbia and BC Children’s Hospital Research Institute followed about 100 infants over four years. They asked parents of five-week-old babies to keep a journal of their child’s behavior — things like crying, sleeping, and feeding. They also asked parents to keep track of how long and how often they gave care to their child that involved physical contact, according to a press release.

When the children were about four and a half years old, the scientists swabbed the inside of their cheeks to take a DNA sample, and then checked to see if there were any differences between children who were touched often as infants and those who were touched less often.

The researchers looked at a process called DNA methylation, the scientists explained in the release. In a body cell, there are structures called chromosomes that contain the genetic code of a person. They determine things like sex, physical appearance, and how the body operates and grows.

In DNA methylation, some parts of the chromosome are “tagged” with molecules that can control how active that portion is, the scientists explained in the release. Scientists can generally predict how this should go as we age.

When they compared the methylation between the children, they found that there were consistent differences between the low-physical-contact and high-physical-contact children. In effect, the cells of the low-contact children were less mature than they should have been given the child’s actual age.

That could result in the child experiencing delays in development and growth, said Michael Kobor, a professor in the Department of Medical Genetics, in the release.

“We plan to follow up on whether the ‘biological immaturity’ we saw in these children carries broad implications for their health, especially their psychological development,” said lead author Sarah Moore in a press release. “If further research confirms this initial finding, it will underscore the importance of providing physical contact, especially for distressed infants.”

In the release, the researchers said the findings are the first that show that touch “has deeply-rooted and potentially lifelong consequences on the epigenome — biochemical changes that affect gene expression.”

But the concept of touch being vital for healthy development is far from new.

One of the most well-known studies on the subject was performed by American psychologist Harry Harlow on rhesus monkeys in the 1950s. Harlow separated monkeys from their real mothers and had them drink milk from either a cold, wire lookalike mother or a different lookalike mother covered in soft cloth. The monkeys spent much more time with the comforting cloth mother, and when Harlow gave them no choice, the monkeys who only had the choice of the cold, wire mother had severe behavioral abnormalities - and they stayed that way even if being introduced to more nurturing environments later, according to a summary from the University of Oregon.

Other studies have found similar results in humans. One found that children who grew up in orphanages away from traditional nurturing had much higher levels of the stress hormone cortisol, and another found that touch-deprived infants have abnormal levels of hormones that regulate social behavior.

The takeaway from the science? Infants need to be held, touched and engaged with to thrive.

“(Engaging with infants) teaches babies basic lessons that they have some agency in the world, so that allows them to explore the world and feel like they can affect their environment as opposed to just being helpless to whatever happens to them,” Ann Bigelow, a professor and researcher of developmental psychology, told Scientific American. “We’re basically a social species, and we learn those things through interacting with others.”