A New Study Has Revealed A Serious Downside To Being A Firstborn Or Only Child

We know that birth order can have a big effect on a person’s experience growing up within their family. It’s not unusual for people to assume that a youngest child will be “babied” and lavished with attention, a middle child forgotten amid the fray or a firstborn bossing around their siblings.

At the intersection between the plight of the firstborn and our gendered expectations of who should take on caregiving duties lies “eldest daughter syndrome,” a non-clinical name for the way these pressures tend to shape the lives and personalities of oldest daughters.

Lisette Schuitemaker, author of The Eldest Daughter Effect: How Firstborn Women Harness Their Strengths, told HuffPost in a previous interview: “Our particular life path makes us into responsible, dutiful, hands-on, thoughtful and caring women.”

Having “been trained to take the lead from a young age,” Schuitemaker continued, it’s not surprising that oldest daughters are overrepresented in positions of leadership. Hillary Clinton, Oprah Winfrey and Beyoncé are some of the oldest daughters Schuitemaker mentions in her book.

There are other effects of being the eldest daughter, however, that are less positive. Girls may be unfairly burdened with caregiving responsibilities because of their gender, becoming “parentified,” or feeling responsible at an early age for duties that would usually fall to a parent.

A new study has identified another way firstborn and only children may be affected by birth order — and this doesn’t apply only to girls. A team at Epic Research analyzed the medical records of over 180,000 children and found that firstborn children with siblings were 48% more likely to have anxiety and 35% more likely to have depression by the age of 8 when compared with children born second or later in their families.

The finding held for only children as well, who were found 42% more likely to have anxiety and 38% more likely to have depression by age 8 when compared with children born second or later. Researchers controlled for other factors, including the child’s and the mother’s mental health histories.

While the study does not examine why firstborns and only children are more likely to receive these diagnoses, it does identify birth order as a potential marker of risk (among many) for anxiety and depression. The finding “adds to our understanding of kids’ risk factors,” Caleb Cox, head of research and data science at Epic Research, told HuffPost.

“Anxiety and depression don’t have a single cause, so understanding what factors are likely to impact a child can help both parents and clinicians to make sure that they are helping the child with their specific needs,” Cox continued. He noted that there are plenty of second- or later-born children who struggle with anxiety and depression as well, “so it’s important for parents to make sure their kids are getting the help that they need, regardless of the child’s birth order.”

There are a couple of possible explanations for how oldest and only children become more likely to have these mental health concerns, and they fall into the familiar categories of nature and nurture.

First, the experiences of children within their families differ based on birth order. Oldest and only children receive their parents’ first attempt at child-rearing, and it can differ substantially from the way they parent subsequent children.

Molly Fox, a biological anthropologist at UCLA, explained that the degree of difference this entails is likely even greater in today’s world than in the past.

“In the pre-Industrial context, the context present for the majority of human history, you would be exposed to parenting and kids your whole life. You would be more involved in caring for your younger siblings,” Fox said. Whereas, lacking this experience, today’s first-time parents, often ridden with anxiety, face a steep learning curve.

These differences in the way they are parented could have an impact on firstborn and only children’s mental health.

Second, we know that the uterine environment has an impact on children’s health and development, and each pregnancy constitutes a unique uterine environment.

“The biological milieu is so different between first and later pregnancies,” Fox said. Cells and fragments of cells from each pregnancy remain in a person’s body long after the baby is born, and each pregnancy essentially rewires a person’s immune system, she noted.

Fox’s research found that a mother’s stress levels during pregnancy predicted an earlier adrenal puberty for eldest daughters, but not for sons. We usually think first of the physical changes that puberty brings, such as hair growth and menstruation, but puberty also involves cognitive and behavioral changes. Maturing earlier in this way could assist eldest daughters with the task of caring for siblings.

It’s possible, Fox said, that “moms who are more depressed, anxious or stressed out during pregnancy could potentially be emitting some biochemical signals in the pregnancy that sets that first daughter up for accelerated maturation.” Here, the eldest daughter is primed for her typical duties before she is even born.

If these biochemical signals of a first pregnancy make eldest daughters enter adrenal puberty at an earlier age, they might also explain firstborn and only children’s increased risk of anxiety and depression.

Fox also noted that a pregnant person’s risk of postpartum depression increases in subsequent pregnancies if they experienced it during their first pregnancy, so it makes sense that there would be a longer-term impact on the mental health of the baby, too.

In terms of the work that firstborns often do in caring for their siblings, Fox explained that, while it may cause stress in our modern culture, such caregiving has been standard practice for most of human history.

Far from being “burdensome and problematic for older children,” she said, “caring for your younger siblings has very deep evolutionary use.” It is one of the ways our species has survived.

“Participating in caring for each other is not an inherently bad thing,” Fox continued, yet “we have set up American society in such a way that’s not compatible with most of our evolutionary family structural elements.”

Rather than being one caregiver in a circle of many, today’s eldest siblings (and their parents) are more isolated from extended family. Having to care for their siblings, in addition to their other responsibilities, can compound stress and affect their mental health.

After a full day of school and chores, caregiving “is something that could end up being quite burdensome” for today’s eldest siblings, not because it is bad on its own but because it may be “incompatible with other expectations,” Fox said.

In other words, parents shouldn’t feel guilty about asking their oldest kids to pitch in, as this is how human families have almost always functioned. There is also evidence that household labor, or doing chores (not specifically related to sibling care) has a positive impact on kids’ mental health, leading to higher self-esteem and more skills for coping with frustration and adversity.

“Being part of the family ecosystem,” Fox said, “is not an unhealthy thing.”This article originally appeared on HuffPost.