Tired toddler mums may finally be able to take some comfort in their exhaustion. It turns out they may have been through a rejuvenation cure by having a baby. At least this is what several Norwegian and international researchers have found in a recent study.

The brains of mothers appeared to be on average between five and six months younger than the brains of their peers with no children.

Advanced brain image analyses enable researchers to calculate brain age with high precision. This technology can provide information about the brain's condition and health.

The brain differences emerged when the researchers examined the brain structure of more than 12 000 British women between the ages of 40 and 70, based on images in a biobank.

More births increase effect

Mothers' brains appeared to be less prone to ageing compared to those of women who had not given birth.

“The positive effect increases with the number of children,” says Ann-Marie G. de Lange, one of the researchers behind the study. She is a postdoctoral fellow at Oxford University and in the Department of Psychology at the University of Oslo (UiO).

However, the effect drops a little for women who have given birth to more than four children. This could be because the sample of women who have more than four children is smaller, or because some of these women belong to a particular demographic.

Wide variation

Pregnancy thus appears to give the brain a boost. And the effect is probably not just short-lived.

“We’re seeing these effects up to 30 years after women have had children. This indicates that they’re long-lasting effects,” says associate professor Lars Tjelta Westlye.

He is part of the Clinical Neuroscience Research Group in UiO’s Department of Psychology and was also involved in the study.

“But,” he adds, “in order to determine this, we have to follow women over time. We did see a lot of variation within the groups, both in women with and without children.”

The researchers are especially interested in investigating the biological and environmental factors that could explain such individual differences in brain aging.

Exciting study

Professor of neurology Erik Taubøll finds the study very exciting. He works at UiO’s Department of Clinical Medicine.

“The study indicates just how plastic the brain is and how it can be affected throughout life. The new thing here is that changes caused by earlier pregnancies bring about permanent changes later in life,” Taubøll writes in an email to forskning.no.

Neuroplasticity, or brain plasticity refers to the brains ability to learn, change and reorganize itself throughout life.

"We know that sex hormones are crucial to the brain's early development", Taubøll adds.

It is also well known that hormonal fluctuations, such as happen with the menstrual cycle, dynamically affect the brain.

The professor thinks the study raises a number of new important questions for understanding the brain's continuous processes of adapting to new conditions throughout its life cycle.

Lots of children, older brain age

Numerous factors in a person's life are influential, and many disruptive factors can affect the results.

“Why, for example, are the results worse for women with lots of children? Other groups have reported an association between lots of children and dementia. What is the reason for that? These factors should now be studied systematically,” according to Taubøll.

The new results provide exciting new knowledge about the brain's constant adaptations and changes even in adulthood.

“As humans, we’re affected by so many factors that we have to be careful about drawing conclusions for everyday life from this. There is still a big difference between statistical significance and practical consequences. But this is exciting research worth following,” Taubøll writes.

Immune system changes

According to Westlye, the childbearing effect was moderate, but that is what researchers expected.

"Childbirth is just one of many factors that can affect brain aging," he says.

A number of biological and psychological changes occur in the mother during pregnancy and childbirth. Both hormonal and immune changes appear to be involved in brain changes that occur during pregnancy and after childbirth.

Several animal studies suggest positive effects from pregnancy. A 2016 study, published in the journal Nature Neuroscience, showed brain changes in women, measured from the time before pregnancy to postpartum.

“These brain changes were related to the mother’s attachment to the child. Greater degrees of brain changes were associated with stronger attachment. The changes lasted up to two years,” de Lange says.

Weaker changes in dads

The researchers have not investigated whether similar changes occur in adoptive mothers in this study.

De Lange believes this would be an interesting question to do follow-up research on.

Some studies show that there may also be changes in the brains of fathers.

“But these changes usually have a slightly different character, and are not as strong as those seen in women who’ve given birth,” de Lange says.

Who has children is no coincidence

This study was not a randomized trial, meaning that researchers cannot necessarily determine the cause and effect of any changes.

“It is important to recognize the limitations of the study design. We controlled for physical and mental illnesses as much as possible, as well as ethnic background, educational level and genetics,” Westlye says.

However, other factors cannot be ruled out.

“It is not random to have or not to have children. However, randomized and controlled trials are very difficult to conduct in such contexts,” he says.

This is one of the reasons why the research group plans to start a study in Oslo, where they will follow women before and throughout pregnancy, and for a period after birth.

Plasticity can also cause vulnerability

Westlye points out that although increased plasticity can be positive in many contexts, it’s not always the case.

“Increased plasticity can also cause vulnerability to environmental pressures, such as changing the amount and quality of sleep and social relationships,” he says.

In some mothers, these stresses combined with the biological changes can increase the risk of mental health problems.

These problems may arise as postpartum depression, for example, which probably affects at least 10 to 15 per cent of mothers, and in rare cases can present as postpartum psychosis.

"It’s important to understand the causes of birth-related mental health problems in order to prevent them and to be able to offer effective treatment both during and after pregnancy," says Westlye.

Want to find cause of postpartum depression

The researchers are now embarking on a study of pregnant women, where they will conduct MRI exams before conception and throughout pregnancy. They will take new pictures of the brain shortly after birth and a couple of years later.

“This will allow us to study the short-term and long-term effects of pregnancy on the mother’s brain and mental health. The study will likely provide new information about risk factors and causes of mental health issues related to birth,” Westlye says.

References:

A. G. de Lange et al.: Population-based neuroimaging reveals traces of childbirth in the maternal brain. Summary. PNAS. 15. October 2019. https://doi.org/10.1073/pnas.1910666116

E. Hoekzema et al.: Pregnancy leads to long-lasting changes in human brain structure. Summary. Nature Neuroscience. 16 December 2016.

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Read the Norwegian version of this article on forskning.no