Can the risk of depression be measured using heart rate?

Major depressive disorder is a very common mental disorder, affecting approximately 265 million people of all ages worldwide (James et al. 2018). Several studies have found a high prevalence of cardiovascular disease in patients with major depressive disorder (Correll et al., 2017; Penninx et al., 2017). Cardiovascular disease poses a global public health challenge, with a significant impact on mortality, hospitalizations, reduced quality of life, work disability, decreased productivity, and increased healthcare costs. Currently, both depression and cardiovascular disease are recognized as the two most prevalent causes of disability in high-income countries, and this trend is expected to extend to other countries worldwide.

In particular, women appear to be the most affected . Women have relative protection against ischemic heart disease until menopause, which is reflected in a lower incidence of acute coronary events during their reproductive years. However, upon entering the postmenopausal stage, there is a greater association between depressive symptoms and the risk of cardiovascular outcomes, including a higher rate of cardiovascular mortality (Veloza et al., 2019).

Numerous studies have demonstrated that major depressive disorder and cardiovascular disease potentially share underlying pathophysiological alterations, such as systemic inflammation, autonomic dysfunction of the hypothalamic-pituitary-adrenal axis (Angermann and Ertl, 2018), and immune system dysregulation (Halaris, 2017). Therefore, it is essential to promote greater awareness of cardiac abnormalities in people with depression. Heart rate parameters can be useful for diagnosing and predicting the severity of depression.

Heart rate and variability in depression

Several studies have focused on heart rate and heart rate variability in major depressive disorder. Heart rate is typically higher during physical activity and lower during rest. Heart rate variability is defined as the fluctuations in time between consecutive heartbeats, known as beat intervals (Shaffer & Ginsberg, 2017). Heart rate and heart rate variability are inversely proportional ; the lower the heart rate, the higher the variability.

This variability results from the influence of the sympathetic and parasympathetic nervous systems on the heart. The sympathetic system activates the body to seek resources and intervene in stressful situations, while the parasympathetic system restores balance once the body has reacted to the emergency situation, following the activation of the sympathetic system.

People with depression tend to have high heart rate levels, even during rest phases, and low levels of heart rate variability.

In general terms, heart rate variability is considered a measure that reflects the body's ability to effectively utilize the cognitive and emotional resources needed to adapt to various environments and react to stressful events.

Specifically, higher heart rate variability has been more directly linked to good emotional regulation (Williams et al., 2015), stronger social skills, and a lower tendency toward rumination (Rottenberg et al., 2007). Meanwhile, different studies have observed that people with depression tend to have the opposite: high heart rate levels (Carney et al., 2008), even during rest, and low levels of heart rate variability (Harmann et al., 2019) due to reduced parasympathetic nervous system activity. This would imply a reduced capacity to cope with stressful events. Therefore, heart rate variability should be considered a potential factor in diagnosing and predicting relapses in depression (Carnevali et al., 2018).

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Measuring the severity of depression using smart devices

The European RADAR-MDD study, published in the journal Physiological Medicine (Siddi, S. et al.), and led by the Mental Health Area of CIBER (CIBERSAM), reveals a connection between the severity of depression and changes in heart rate in people with a history of recurrent major depressive disorder.

The project studied heart rate variability in 510 people with major depression over a period of up to two years. These individuals wore a smart bracelet day and night and completed a mood questionnaire every two weeks. The bracelet allowed researchers to study heart rate during periods of physical activity, measured by steps, and during periods of rest. The key finding of this study is that more severe depression is associated with less heart rate variability during rest periods throughout the day and a higher heart rate during rest periods at night. In other words, people with higher levels of depression tend to have a higher heart rate at night and less heart rate variability at rest throughout the day.

The European RADAR-MDD study reveals a connection between the   severity of depression and changes in heart rate.

When analyzing this data, several factors that can influence heart rate were taken into account, such as gender, age, body mass index, and alcohol or tobacco consumption, as well as the presence of other medical conditions associated with depression and the use of antidepressant medications. However, other factors that were not considered could have played a significant role in altering heart rate, such as some of the symptoms of depression itself, like sleep difficulties (insomnia and hypersomnia) or high levels of anxiety and sedentary behavior. For this reason, future research should explore the impact of these factors, among others, on the association between heart rate and the severity of depression, while also considering the limitations of these technologies.

The findings of this study, combined with other factors, will allow for early detection of possible depressive episodes in the future and will trigger an alert to receive preventive and personalized professional care.

People with higher levels of depression tend to have a high heart rate at night and less variation in resting heart rate throughout the day.

The RADAR-MDD study is part of the international project Remote Assessment of Disease and Relapse in Central Nervous System Disorders (RADAR-CNS) , which This project investigates new ways to measure major depressive disorder, epilepsy, and multiple sclerosis using wearable devices and smartphone technology. It aims to improve the quality of life for people with these conditions and change how they are managed and treated. Data collected through mobile devices can provide a comprehensive picture of a person's condition with a level of detail previously impossible. This offers the possibility of detecting changes in behavior, sleep, or mood before the individual is even aware of them. This could help predict or even prevent a relapse .

RADAR-CNS has brought together clinicians, researchers, engineers, computer scientists and bioinformaticians from around the world and 22 organizations from Europe and the United States.

We thank all participants in this study for their valuable collaboration, which has been fundamental to the advancement of knowledge in this area.