A new, comprehensive definition of loneliness aims to provide a clear foundation for tackling what public health officials have called a global crisis. A researcher at the University of Dundee has developed a precise clinical and social description of the condition, intended to guide more effective policy, channel support to those in need, and standardize future research into a problem that affects hundreds of millions of people worldwide.
The lack of a shared, specific understanding of loneliness has long been a barrier to addressing the issue, according to the research. Without a consensus on what loneliness is, governments, health care professionals, and support organizations have struggled to know where to target funding and resources. This new definition seeks to resolve that ambiguity, creating a common language and framework for a condition whose health impacts are increasingly compared to those of smoking and obesity.
A Pervasive Public Health Issue
In recent years, awareness of loneliness has surged, particularly after the widespread social disruptions of the COVID-19 pandemic. The World Health Organization now recognizes social isolation and loneliness as a priority public health problem affecting all age groups. Statistics reveal the scale of the issue, with an estimated one in six people worldwide experiencing loneliness. In the United States, about one in three adults reports feeling lonely. This is not merely a fleeting emotional state but a chronic condition with severe consequences.
The U.S. Surgeon General has issued a formal advisory on the crisis, highlighting evidence that social disconnection significantly increases the risk for premature death, with a mortality impact similar to that caused by smoking up to 15 cigarettes a day. The health risks associated with loneliness are even greater than those linked to obesity and physical inactivity, making it one of the most significant public health challenges of the modern era. A 2024 government survey in England found that more than 3 million people identified as feeling lonely “often or always.”
Crafting a Foundational Definition
Dr. Kathryn Cunningham, from the University of Dundee’s School of Health Sciences, developed the new definition after more than a decade of study, examining texts across medicine, psychology, and philosophy. Published in the journal Health Psychology Review, the research defines loneliness as “the negative feeling(s) one experiences as a result of a (conscious or subconscious) personal perception that one’s interpersonal needs are not satisfied by (the quantity and/or quality of) one’s interpersonal (emotional, social, collective, professional and/or religious) relationships.”
Cunningham emphasized that a problem cannot be solved if it is not fully understood. By establishing a single, precise definition, the goal is to create a stable foundation for action. This allows policymakers to design better-informed strategies, enables health and social care professionals to identify and support individuals more effectively, and provides a consistent baseline for future scientific studies. The standardization is critical for ensuring that resources are channeled appropriately and that interventions are genuinely effective.
The Severe Impacts on Physical Health
A vast body of evidence demonstrates that loneliness and social isolation are profoundly damaging to physical health. The effects are systemic, impacting everything from cardiovascular function to the immune system. This new, clearer definition helps contextualize the urgency of addressing a condition with such far-reaching physiological consequences.
Cardiovascular and Metabolic Risks
Research summarized by the American Heart Association shows a strong link between loneliness and poor cardiovascular outcomes. Loneliness is associated with a 29% increased risk of heart attack and a 32% increased risk of stroke. Furthermore, for individuals who already have coronary heart disease, social isolation and loneliness are linked to a worse prognosis. The condition is also associated with high blood pressure, systemic inflammation, and an elevated risk for developing type 2 diabetes.
Immune Response and Cognitive Health
Beyond heart health, loneliness can weaken the body’s defenses. Studies show it is connected to reduced immunity against infections and poorer sleep quality, which is critical for physical and mental restoration. The Centers for Disease Control and Prevention also lists dementia as a potential long-term consequence of loneliness, highlighting its detrimental effect on brain health.
Clarifying Important Nuances
A key strength of the new definition is its precision, which helps untangle loneliness from other related, but distinct, concepts. This clarity is essential for accurate diagnosis and effective support, ensuring that interventions target the actual problem of loneliness rather than adjacent issues.
Loneliness vs. Social Isolation
It is critical to distinguish between being lonely and being socially isolated. Social isolation is an objective state characterized by a lack of social contact with others. Loneliness, however, is a subjective feeling. As Cunningham’s definition specifies, it is a personal perception that one’s interpersonal needs are not being met. An individual can be surrounded by many people and still feel intensely lonely if those relationships lack quality or meaning. Conversely, a person can lead a relatively isolated life with few social contacts and not feel lonely at all.
A Distinct Experience from Depression
While loneliness is closely linked to depression and can be a contributing factor, the two are not the same. Depression is a broader mood disorder with a wider range of symptoms. Loneliness is specifically rooted in the negative feelings that arise from dissatisfaction with one’s relationships. An individual experiencing these feelings may then develop depression, but the initial cause is the perceived deficit in social connection.
A New Framework for Society
The implications of this unified definition extend beyond the clinic and into the fabric of society. Dr. Cunningham noted that policy focused on loneliness should impact wider areas, including education and even town planning, to foster environments that encourage meaningful social connection. The personal experience of Margaret, a woman featured in the research, powerfully illustrates this complexity. After losing her husband and retiring, she felt a profound emptiness that could not be solved by simply joining a club. She explained that she could be in a room with a million people and still feel empty, emphasizing the need for meaningful relationships.
Her experience also touches on the loss of identity—as a wife and a worker—that contributed to her sense of loneliness, showing it is far more complex than the mere absence of people. This new, nuanced definition validates such experiences and provides a framework for developing more sophisticated advice and support options that address the quality, not just the quantity, of social interactions.
The Path Forward
With a clear and comprehensive definition now established, researchers and public health officials are better equipped to combat the global loneliness crisis. It provides the necessary underpinning for a new generation of research that can more accurately measure the condition and test the effectiveness of different interventions. For governments and organizations, it offers a shared understanding from which to build policies that promote social connection as a fundamental component of public well-being. By standardizing the concept, this work can help ensure that the millions suffering in silence receive more targeted and effective support.
