PhD defence I.K. (Isabel) Schuurmans

Brief summary of the doctoral thesis:

Maintaining brain health is crucial for our physical and mental well-being throughout our whole lives. Beyond well-known lifestyle factors such as not smoking, exercising, and maintaining a healthy weight, there are additional factors that could contribute to brain health. In this dissertation, we investigated the effects of early life stress and mental health on the brain from fetal to old life in the general population. We also explored the underlying molecular mechanisms using data from the Generation R Study and the Rotterdam Study.

Early and middle-life stress was indeed associated with poorer brain health. More specifically, in children, early stress was often linked to lower academic performance than expected based on IQ. In adult women, life stress was associated with lower cognitive and brain reserve, indicating increased vulnerability to neurodegenerative diseases. Additionally, we found that mental health problems, particularly attention issues at six years old, were linked to academic performance at twelve years old. The relationship between prolonged depressive symptoms in adults and brain health was less convincing, though individuals with increasing depressive symptoms had a thicker cortex in a small part of the right lateral occipital cortex. In later life, older adults with more brain damage were also more likely to have depressive symptoms.

The dissertation concluded with an in-depth investigation into the possible mechanisms underlying brain health. We examined the role of the gut-brain axis but found no convincing relationship between gut microbiome and mental health in children. We also studied DNA methylation, a biological layer that forms around DNA and can ‘turn on and off’ genes in response to the environment. We discovered that genetic vulnerability to mental health issues is already evident in changes in DNA methylation immediately after birth.

In summary, this dissertation highlights the complex interactions between early life stress, mental health, and brain health throughout the lifespan, shedding light on the underlying molecular mechanisms. This research paves the way for future studies and call for fostering optimal brain function from early life onwards, as this might enable individuals to realize their full potential throughout their lives.