Study: "Combined Influences of Genes, Prenatal Environment, Cortisol, and Parenting on the Development of Children’s Internalizing Versus Externalizing Problems"

The study "Combined Influences of Genes, Prenatal Environment, Cortisol, and Parenting on the Development of Children’s Internalizing Versus Externalizing Problems" (authors: Kristin Marceau, Heidemarie Laurent et al.) examined how various factors — genes, the prenatal environment, the hormone cortisol, and parenting style — together influence the development of internalizing (inward — anxiety, depression) and externalizing (outward — aggression, hyperactivity) problems in children.

The Study — Simple and Step-by-Step

1. Unique Design:

– Included 361 adopted children; both biological and adoptive parents participated.
– Allowed researchers to separate the influence of genes/prenatal environment from parenting style.

2. Genetic Risk:
– Assessed by the history of mental problems in biomama (hereditary risk).

3. Prenatal Factors:
– Monitoring maternal drug use and depression/anxiety levels during pregnancy.

4. Cortisol Levels:
– Measured morning cortisol in children at 4.5 years old — a hormone linked to stress.

5. Parenting Style:
– The "heightened reactivity" of adoptive parents throughout childhood (e.g., angry outbursts, strictness) was studied.

6. Outcome at Age 6:
– Determined by the behavior scale: internal (anxiety, sadness) and external (aggression, oppositional behavior).

Main Findings

1. Externalizing problems (outward behavior):

— The most significant influence was only the parenting style (overreactive parental responses), regardless of genetics or cortisol levels.

2. Internalizing problems (inward issues):
— These were linked to a cascade of influences:

Genetics → worsening of prenatal factors → elevated morning cortisol → internalizing problems.

Parenting style affected outcomes in two ways: directly, and indirectly through elevated morning cortisol.

Conclusions

Different mechanisms underlie different types of problems:

• External behavioral difficulties are primarily formed due to inconsistent and overreactive parenting.
• Internal emotional disorders result from a combination of genetic predisposition, adverse prenatal environment, and high cortisol levels.

Cortisol as a key mediator:
— It reflects both genetic and parental stress load, especially in relation to anxiety and depression.

What this means in practice

When a child shows signs of internal anxiety, it is important to consider:

• their hereditary predisposition,
• healthy prenatal conditions, and
• current stress levels (cortisol).

To address external behavioral manifestations, it is helpful to train parents in controlled, clear, and consistent responses.

Translation of Key Terms

• Internalizing problems – inward issues (anxiety, depression)
• Externalizing problems – outward issues (aggressive, hyperactive behavior)
• Morning cortisol – child’s cortisol level in the morning, a stress marker
• Overreactive parenting – intense, often exaggerated parental responses

Why this matters

This is the first major study using an adoption-based research design to analyze the effects of:

• biological predisposition,
• prenatal factors (e.g., maternal substance use),
• hormonal mechanisms (cortisol),
• parenting style.

The authors demonstrated that a combination of factors (genes, hormones, environment) contributes to a child’s vulnerability to internalizing problems, while parental behavior is the key factor in shaping external behavioral issues.

Link to the Original Study

Kristin Marceau, Heidemarie K. Laurent, Jenae M. Neiderhiser, David Reiss, Daniel S. Shaw, Misaki Natsuaki, Philip A. Fisher, and Leslie D. Leve (2015). Combined effects of genes, prenatal environment, cortisol, and parenting on the development of children’s internalizing and externalizing problems. Behavior Genetics, 45(3), 268–282.