Nurture may trump nature when it comes to depression risks

Nature versus nurture is an age-old debate, but a recent study attempts to settle the argument—at least in terms of depression risks.

The study, published in the American Journal of Psychiatry, followed more than 3200 pairs of siblings from a Swedish health registry to find out whether depression risk was linked more closely to a child’s genes or their environment.¹

The research team analyzed data from nearly 700 full siblings and 2600 half-sibling pairs who had at least 1 birth parent diagnosed with depression. These sibling pairs were unique, though, in that each pair had 1 child who was raised at home with biological parents and another who was raised in an adoptive home that was “supportive and generally advantaged,” and found by the team to have a protective effect against depression.

The goal of the study was to more closely examine this idea of nature versus nurture, says Kenneth Kendler, MD, professor of psychiatry at Virginia Commonwealth University in Richmond, and co-author of the study. Kendler says that Sweden was an ideal place to study sibling pairs because there are more adoptive parents than children to adopt. This provided a large study sample of an adoptive population that is subject to strict adoption standards.

He says this is the first study to examine matched siblings in different home environments. The way the study was designed provides unique insight on the causal effects of depression and possibly other psychiatric disorders, he says.

There has been intense study on the origins of depression, and whether DNA variants may be responsible for underlying genetic risks and familial trends. However, there has been little research that has been able to look as closely as this one at environmental impacts.

In this study, the research team found that full siblings raised in the adoptive homes were 23% less likely to be treated for major depression. Half-siblings raised in adoptive homes were 19% less likely to be treated for depression.

Not all adoptive environments are equal, though, the research team observed.

“Although major depression has important biological and genetic components, the study shows evidence that rearing children in a nurturing environment also matters,” Kendler says. “This is strong evidence that shows that rearing factors are important.”

According to the report, the reduced depression risk didn’t apply in adoptive households where 1 of the members of the household developed depression, or in cases of death or divorce within the adoptive family.

Kendler says he hopes the study emphasizes the need to pay close attention and devote efforts toward improving home environments for high-risk families in terms of depression prevention.

“We know from other studies that people who perceive their parents as being warm and loving as children have a reduced risk for depression,” Kendler adds. “A warm and loving environment can give us reserves for the rest of our adult lives. It gives us a certain amount of resilience that helps us do a better job when struggling with adversity along with experiences in our adult life.”

Reference

1. Kendler K, Ohlsson H, Sundquist J, Sundquist K. The rearing environment and risk for major depression: a Swedish national high-risk home-reared and adopted-away co-sibling control study. American Journal of Psychiatry. 2020:177(5):447-453. doi:10.1176/appi.ajp.2019.19090911