How Our Internal Clock Affects Our Mood

Research Spotlight Blog No. 10

Valentina Paz holds a BSc in Psychology from the Universidad de la República (Uruguay), and both an MSc and a PhD in Biological Sciences (Neurosciences) from the Program for the Development of Basic Sciences in Uruguay. She is a lecturer at Universidad de la República and an honorary research fellow at the University of Liverpool.

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When I think about how I ended up studying circadian rhythms and mental health, it always feels both unexpected and, somehow, perfectly timed. Mental health conditions affect hundreds of millions of people worldwide, but in Uruguay—the place where I was born and trained—they represent an especially urgent public concern. The country faces an alarming reality: suicide rates are among the highest in Latin America. Against this backdrop, depression naturally became the focus of my research—a condition that affects millions, stands as the leading cause of disability, and can, tragically, be fatal. Growing evidence suggests that disruptions in our circadian rhythms play a crucial role in the onset, persistence, and severity of depression, highlighting the internal clock as a key to understanding—and hopefully preventing—this disorder.

My doctoral journey started in 2019 when I had my first meeting with Dr. Ana Silva and Dr. Bettina Tassino, who lead the Chronobiology Group at Universidad de la República, Uruguay. They welcomed me into their team and invited me to the XV Latin American Symposium on Chronobiology, held that same year in Colonia, Uruguay. I went there knowing almost nothing about chronobiology. At that symposium, I met Dr Victoria Garfield—a Uruguayan-British researcher then based at University College London—who, despite not knowing me, kindly offered to share her papers and opened the door to collaboration. The doors of all three of these inspiring women scientists remain open to this day, and for that, I will always be deeply grateful.

In my doctoral research, I explored the relationship between the circadian system and depression from multiple angles. I examined whether disturbances in circadian rhythms play a causal role in depression using a genetic epidemiology approach known as Mendelian randomisation, and I also investigated the nature of these disruptions in Uruguayan youth—an advantageous model given their pronounced eveningness. Using a combination of self-report questionnaires, sleep diaries, actigraphy, and physiological measures, including melatonin, cortisol, and body temperature rhythms, I found that depression is linked to alterations in circadian rhythms, particularly a tendency toward eveningness, poor sleep quality and duration, and the presence of insomnia symptoms. A bidirectional causal relationship emerged between depression and insomnia, indicating a bidirectional association. There was also modest evidence for a causal link between morningness and a lower likelihood of depression, as well as an effect of depression on shorter sleep duration. It was demanding work—spanning Uruguay and the UK, bridging multiple methods, and navigating two languages—but it was also deeply fulfilling.

Light and dark

Over time, this work expanded into other populations and questions. I’ve studied how disturbances in circadian rhythms and mood manifest among dance students in Uruguay—a group exposed to demanding schedules and intense physical training. I also integrated polygenic and lifestyle information to understand how sleep influences multiple health outcomes at the population level. In addition, I wrote a review on selecting genetic instruments for Mendelian Randomisation studies of sleep traits, and I have participated in research exploring links between circadian rhythms and anorexia nervosa, as well as in a genome-wide association study of composite sleep. I’ve also examined the connection between daytime napping, cognitive function, and brain volume—a study that unexpectedly reached an international audience. It was featured in more than 680 news stories across media outlets such as the BBC, CNN, The Guardian, The Times, and CBS News, spanning North and South America, Europe, Asia, and Africa. It was a reminder of how deeply sleep resonates with people everywhere.

Throughout my PhD, I had the privilege of training abroad. In 2021, I spent three months in London during an internship at the MRC Unit for Lifelong Health and Ageing (University College London), where Dr Garfield introduced me to a vibrant, collaborative research environment. Later, in 2023, I visited the Center for Genomic Medicine at Harvard Medical School under the guidance of Dr Hassan Dashti, who generously included me in his projects. Most recently, in 2024 and 2025, I spent time at the Department of Pharmacology and Therapeutics at the University of Liverpool, where I was welcomed into an inspiring and diverse research group. Alongside my scientific work, I also trained in Cognitive Behavioural Therapy—an experience that allows me to see the people behind the data.

Today, I work at the intersection of chronobiology and psychology, trying to understand how disruptions in the circadian system shape vulnerability to mental disorders. Across all these projects, my goal remains the same: to deepen our understanding of mental illness so we can develop more effective strategies for prevention, diagnosis, and treatment. Working in this field has allowed me to collaborate with researchers from diverse disciplines and to travel to fascinating places, such as Scotland, where I attended the Circadian Mental Health Network Conference in 2025, supported by the network. Moving forward, I hope my work keeps building bridges—between basic science and clinical practice, and between light and shadow, where the rhythms that define us take shape.

Blog by Valentina Paz