Why Is Mental Health Important? Effects on Physical Health, Work, and Daily Life

Mental health is important because it determines how people think, feel, and function across every domain of life — from the ability to manage stress and maintain relationships to physical health outcomes, workplace productivity, and longevity. The World Health Organization (WHO) defines mental health not as the mere absence of a mental disorder, but as “a state of well-being in which the individual realizes their own abilities, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to their community” (WHO, 2022).

Mental health matters at a population level too. The WHO Mental Health Atlas 2024 — based on surveys of 144 countries and released in September 2025 — found that over one billion people worldwide are now living with a mental health condition, making mental illness the leading cause of disability globally. Depression and anxiety alone cost the global economy an estimated US$1 trillion each year in lost productivity, yet median government spending on mental health remains at just 2% of total health budgets — unchanged since 2017 (WHO, 2025).

KEY HIGHLIGHTS

• Mental health is not the absence of disorder: The WHO and CDC now define mental health as a positive state of well-being and functioning — not simply the absence of a diagnosed condition. A person can have a mental health condition and still experience positive well-being with the right support (CDC, 2024; WHO, 2022).
• Over one billion people are affected globally: The WHO Mental Health Atlas 2024 confirmed that more than 1 billion people worldwide are living with a mental health condition — a figure that has increased significantly since 2020. Mental disorders are the second biggest contributor to years lost to disability globally (WHO, 2025).
• Mental and physical health are bidirectionally linked: People with severe mental illness are 1.84 times more likely to experience physical multimorbidity (multiple co-occurring chronic physical conditions) than people without mental illness, based on a 2023 meta-analysis of 194,123 psychiatric patients (Pizzol et al., 2023).
• Untreated mental illness extracts severe economic costs: Depression and anxiety cost the global economy US$1 trillion annually in lost productivity, representing 12 billion lost working days per year. For every $1 invested in scaled-up treatment for depression and anxiety, there is a $4 return in improved health and productivity (WHO, 2022).
• The treatment gap remains enormous: A 2024 West Health/Gallup survey found that 75% of U.S. adults believe mental health conditions are identified and treated worse than physical health conditions. Despite being highly treatable, fewer than half of people with mental health conditions worldwide receive any care (AAMC, 2025).
• Mental health shapes physical health through measurable biological pathways: Chronic psychological stress dysregulates the HPA (hypothalamic-pituitary-adrenal) axis — the brain-body stress hormone system — producing sustained elevation of cortisol (the body’s primary stress hormone) that increases inflammation, weakens immune function, and accelerates cardiovascular disease risk (NIMH, 2024).
• Early support produces lasting gains: Mental health conditions most commonly emerge before age 25; approximately 50% of all lifetime mental health conditions begin by age 14. Early identification and support during these critical developmental windows significantly improve long-term health, educational, and occupational outcomes (WHO, 2025).

What Is Mental Health, and Why Is It More Than the Absence of Illness?

Mental health is a dynamic state of psychological well-being that encompasses emotional, psychological, and social functioning — and critically, it exists on a continuum rather than as a binary condition. The WHO definition frames it as the presence of positive functioning, not simply the absence of disorder: a person who has never been diagnosed with a mental illness is not automatically mentally healthy, just as a person with a diagnosed condition is not automatically without well-being (WHO, 2022).

This distinction has an important clinical grounding. The two-continua model of mental health, validated by Westerhof and Keyes (2010) using data from a representative survey of 3,032 American adults, demonstrates that mental health and mental illness are related but distinct dimensions. One continuum runs from mentally ill to not mentally ill. A separate and independent continuum runs from languishing (poor positive mental health despite no diagnosable disorder) to flourishing (high positive mental health even in the presence of a condition). Research confirmed that the predictors of flourishing — strong social relationships, sense of purpose, meaningful activity — are distinct from the predictors of mental illness, meaning they require separate attention and different interventions (Westerhof & Keyes, 2010).

Practically, this means that mental health is not just a clinical concern for people in crisis. It is a daily health resource — one that determines how well people concentrate, regulate emotions, maintain relationships, make decisions, and recover from adversity. The CDC frames this as “the ability to thrive,” and notes that improving positive mental health is achievable even for people living with diagnosed conditions when they have access to effective treatment and stable, supportive environments (CDC, 2024).

How Does Mental Health Affect Physical Health?

Mental health affects physical health through several direct and indirect biological pathways, and the relationship runs in both directions: poor mental health worsens physical health outcomes, and poor physical health is a significant risk factor for developing mental health conditions.

The primary biological mechanism linking mental and physical health is the HPA axis — the hypothalamic-pituitary-adrenal axis, which is the brain’s central stress-response system. Under chronic psychological stress, the HPA axis produces persistently elevated cortisol (the body’s main stress hormone). Sustained cortisol elevation suppresses immune system function, increases systemic inflammation (chronic low-level immune activation throughout the body), raises blood pressure, impairs metabolic regulation, and accelerates cardiovascular damage. These physiological effects — not lifestyle choices alone — explain why people with chronic depression, anxiety disorders, or serious mental illness have disproportionately high rates of heart disease, type 2 diabetes, and autoimmune conditions (NIMH, 2024).

The population-level evidence is stark. A 2023 meta-analysis published in BMJ Mental Health, drawing on data from 194,123 psychiatric patients across 19 studies and comparing them to 7.66 million control participants, found that people with severe mental illness were 1.84 times more likely to experience physical multimorbidity than those without mental illness. Conditions identified at elevated rates included metabolic diseases, hypertension, epilepsy, and respiratory disorders (Pizzol et al., 2023). Additionally, the Mental Health Foundation reports that nearly one in three people with a long-term physical health condition also has a co-occurring mental health problem, most commonly depression or anxiety — creating compounding effects that worsen outcomes for both conditions simultaneously.

NIMH research also confirms that depression specifically is both a consequence and a driver of chronic physical illness: people with chronic conditions such as diabetes, heart disease, and cancer develop depression at significantly higher rates than the general population, and the presence of depression in turn reduces treatment adherence, worsens prognosis, and increases mortality in those chronic disease populations (NIMH, 2024).

How Does Mental Health Affect Workplace Productivity and the Economy?

The economic importance of mental health is measurable and substantial. Mental health conditions are the second leading cause of long-term disability globally, and their impact on work performance represents a cost that far exceeds the direct costs of treatment.

WHO data shows that depression and anxiety account for an estimated 12 billion lost working days every year, costing the global economy approximately US$1 trillion annually — predominantly through lost productivity rather than direct healthcare expenditure. Approximately 15% of working-age adults worldwide are living with a mental disorder at any given time (WHO, 2022). This burden manifests in two forms: absenteeism (not attending work) and presenteeism (attending work while significantly impaired, producing reduced output without visibly missing time).

In the United States specifically, the scale is also significant. Survey data reported in 2024 found that approximately 75% of workers experienced some form of mental health challenge in the past year, with Gen Z workers disproportionately affected. The economic consequence is borne not only by individuals but by organizations and public health systems: untreated mental illness drives higher rates of staff turnover, greater use of disability leave, and increased healthcare utilization across all specialties — not just mental health services (WHO, 2022).

Critically, the economic case for investment in mental health is also positive. WHO analysis demonstrates that for every US$1 invested in scaled-up treatment for depression and anxiety, there is a US$4 return in improved health and productivity. This return on investment makes mental health support one of the most cost-effective interventions available to employers, health systems, and governments (WHO, 2022).

The table below summarizes the documented costs of untreated mental illness across key domains alongside the measurable benefits of treatment and support:

Domain	Cost of Untreated Mental Illness	Benefit of Treatment / Support
Global Economy	Depression and anxiety alone cost US$1 trillion annually in lost productivity (WHO, 2025)	$4 return in improved health and productivity for every $1 invested in scaled-up treatment (WHO, 2022)
Physical Health	People with severe mental illness are 1.84x more likely to have physical multimorbidity — multiple co-occurring chronic conditions (Pizzol et al., 2023)	Treating depression alongside chronic illness improves treatment adherence and reduces overall healthcare costs (NIMH, 2024)
Workplace	12 billion working days lost every year to depression and anxiety; 15% of working-age adults have a mental disorder at any point in time (WHO, 2022)	Workplace mental health programs reduce absenteeism, presenteeism (working while unwell), and staff turnover (WHO, 2022)
Life Expectancy	Serious mental illness is associated with a life expectancy 10–25 years shorter than the general population, driven by physical comorbidities and reduced healthcare access (NAMI, 2023)	Early identification and consistent treatment reduces mortality gap and improves functioning across the lifespan (WHO, 2025)
Healthcare System	Untreated mental illness drives higher emergency department use, longer hospital stays, and greater total health expenditure (OECD, 2024)	Integrated physical and mental healthcare models lower total system costs and produce better patient outcomes (AAMC, 2025)

How Does Mental Health Affect Relationships and Social Functioning?

Mental health affects relationships and social functioning because the psychological capacities underlying social connection — emotional regulation, empathy, communication, and the ability to tolerate uncertainty and conflict — are all dependent on well-functioning mental health.

When mental health is poor, the social consequences are pervasive. Depression reduces motivation for social engagement, produces emotional flatness that makes connection feel impossible, and generates negative self-evaluation that distorts how a person interprets others’ behavior. Anxiety disorders drive avoidance of social situations and hypervigilance to signs of threat or rejection within relationships. PTSD (post-traumatic stress disorder) fundamentally disrupts trust and the ability to feel safe with other people. These effects are not failures of personality or character — they reflect how mental health conditions alter the brain circuits responsible for social cognition (the mental processes underlying how we understand other people and navigate social situations).

Conversely, strong social relationships are one of the most consistently identified protective factors for mental health. The same WHO Mental Health Atlas 2024 framework that documents the burden of mental illness also highlights that social connectedness, belonging, and access to stable, supportive relationships are primary determinants of whether individuals maintain positive mental health across the lifespan. Loneliness and social isolation — now increasingly recognized as public health concerns of their own — significantly elevate the risk of depression, anxiety, cognitive decline, and cardiovascular disease, reinforcing the bidirectional relationship between social functioning and mental well-being (WHO, 2025).

Why Does Mental Health Matter at Every Stage of Life?

Mental health matters at every stage of life because the developmental windows during which mental health is established are also the windows during which foundational capacities — emotional regulation, academic achievement, attachment security, identity formation, and occupational functioning — are built. Disruptions during these critical periods produce effects that compound across the lifespan.

In childhood and adolescence (ages 5–17), mental health underpins learning, social development, and the formation of behavioral habits that carry into adulthood. WHO data confirms that 50% of all lifetime mental health conditions begin by age 14, and 75% by age 24. Mental ill-health is the leading cause of disability in young people aged 10–24, contributing up to 45% of the overall burden of disease in this age group. Conditions that go undetected and unsupported in school settings — including depression, anxiety, ADHD, and trauma responses — produce downstream consequences in educational attainment, employment, and long-term health (WHO, 2025).

In working adulthood (ages 25–64), mental health determines occupational performance, relationship stability, and the ability to manage the financial, social, and caregiving demands that characterize these years. Approximately 15% of working-age adults have a mental disorder at any point in time, and many more experience subsyndromal symptoms (symptoms that are real and impairing but do not meet full diagnostic criteria) that affect their functioning without generating a formal diagnosis or treatment (WHO, 2022).

In older adulthood (ages 65+), mental health is critically linked to cognitive functioning, physical health management, and the ability to maintain independence. Depression in older adults is associated with accelerated cognitive decline, poor management of chronic conditions, and significantly elevated mortality. Despite this, mental health conditions in older adults are systematically under-identified: many are attributed to “normal aging” rather than recognized as treatable conditions (CDC, 2024).

How Does Mental Health Affect Daily Functioning and Quality of Life?

Mental health affects daily functioning through its influence on cognition, motivation, emotional regulation, and the capacity to engage meaningfully with work, relationships, and personal goals. These effects are not abstract — they translate into measurable differences in how well people perform routine tasks, manage stress, sustain attention, make decisions, and experience satisfaction from everyday activities.

The CDC identifies three domains that mental health shapes directly: emotional well-being (the ability to experience and process a range of emotions adaptively), psychological well-being (having a sense of purpose, mastery, personal growth, and self-acceptance), and social well-being (the ability to connect with and contribute to a broader community) (CDC, 2024). Deficits in any of these domains — even without a diagnosable mental illness — produce measurable reductions in quality of life and in the ability to function effectively. This is why positive mental health is not a luxury or an ideal but a functional health resource with direct consequences for daily living.

Sleep is one of the most sensitive indicators of mental health status. Anxiety and depression are the two leading causes of insomnia — the inability to fall or stay asleep — and sleep disruption in turn worsens both conditions, creating a self-reinforcing cycle. Poor sleep quality impairs memory consolidation, emotional regulation, immune function, and metabolic health; its effects on cognition are measurable after as little as one or two nights of insufficient sleep, and chronic sleep deprivation produces cognitive impairment comparable to elevated blood alcohol concentration (CDC, 2024).

When Does Mental Health Become a Medical Concern That Warrants Professional Attention?

Mental health becomes a medical concern warranting professional evaluation when changes in emotional, cognitive, behavioral, or physical functioning persist beyond what is expected following a stressful event, cause meaningful disruption to daily life, or involve any of the following indicators:

• Persistent low mood or anxiety: Feelings of sadness, emptiness, hopelessness, or excessive worry that last for two weeks or more and are present most of the day are among the most reliable indicators that professional evaluation is warranted — these match the minimum duration criteria for major depressive disorder and generalized anxiety disorder in the DSM-5 (American Psychiatric Association, 2022).
• Functional impairment: Difficulty meeting responsibilities at work, school, or home — not driven by external circumstances but by persistent internal distress, low motivation, concentration difficulties, or emotional dysregulation — signals that mental health is interfering with functioning at a clinically significant level.
• Physical symptoms without medical explanation: Chronic headaches, gastrointestinal disturbance, persistent fatigue, or cardiovascular symptoms that a physician cannot attribute to a physical cause are common somatic (body-based) expressions of anxiety and depression, and should prompt evaluation that includes mental health screening.
• Changes in sleep or appetite: Significant and sustained disruption to normal sleep patterns or appetite — particularly if accompanied by mood changes, withdrawal from previously enjoyed activities, or increasing social isolation — should not be attributed to stress alone without professional assessment.
• Thoughts of self-harm or suicide: Any thoughts of ending one’s life or harming oneself warrant immediate evaluation. Call or text 988 (the Suicide and Crisis Lifeline) 24 hours a day, 7 days a week, free and confidential, or go to the nearest emergency department.

The most important first step is speaking with a primary care physician or licensed mental health professional — such as a psychologist, licensed clinical social worker (LCSW), or psychiatrist — who can conduct a structured assessment. Free, validated online screening tools such as Mental Health America’s anonymous screening platform (MHAscreening.org) can help individuals gauge whether their experiences suggest a condition worth discussing with a clinician.

WHAT TO DO NEXT

Mental health is not a peripheral concern — it is a core dimension of human health with direct, measurable consequences for physical health, relationships, work, and lifespan. The WHO definition frames it as a positive state of well-being essential for realizing one’s abilities and contributing to society. The evidence base supporting its importance spans neuroscience, economics, epidemiology, and developmental psychology, and is growing more robust every year.

If you or someone you care about is experiencing symptoms that are interfering with daily functioning, speak with a primary care provider or licensed mental health professional. If you are in crisis, call or text 988 — the Suicide and Crisis Lifeline — available 24 hours a day, 7 days a week, free and confidential.

REFERENCES

American Psychiatric Association. (2022). Diagnostic and statistical manual of mental disorders (5th ed., text rev.). American Psychiatric Association Publishing. https://doi.org/10.1176/appi.books.9780890425787

Association of American Medical Colleges. (2025, February 6). Mental health is part of physical health. Why isn’t it treated as such? https://www.aamc.org/news/mental-health-part-physical-health-why-isn-t-it-treated-such

Centers for Disease Control and Prevention. (2024). About mental health. https://www.cdc.gov/mental-health/about/index.html

National Alliance on Mental Illness. (2023). Mental health by the numbers. https://www.nami.org/about-mental-illness/mental-health-by-the-numbers/

National Institute of Mental Health. (2024). Understanding the link between chronic disease and depression. U.S. Department of Health and Human Services. https://www.nimh.nih.gov/health/publications/chronic-illness-mental-health

Organisation for Economic Co-operation and Development. (2024). The emergence of mental ill-health and its societal and economic impacts. In Mental Health Promotion and Prevention. OECD Publishing. https://doi.org/10.1787/88bbe914-en

Pizzol, D., Trott, M., Butler, L., Barnett, Y., Ford, T., Neufeld, S. A. S., Ragnhildstveit, A., Parris, C. N., Underwood, B. R., Lopez Sanchez, G. F., Fossey, M., Brayne, C., Fernandez-Egea, E., Fond, G., Boyer, L., Shin, J. I., Pardhan, S., & Smith, L. (2023). Relationship between severe mental illness and physical multimorbidity: A meta-analysis and call for action. BMJ Mental Health, 26(1), e300870. https://doi.org/10.1136/bmjment-2023-300870

Westerhof, G. J., & Keyes, C. L. M. (2010). Mental illness and mental health: The two continua model across the lifespan. Journal of Adult Development, 17(2), 110–119. https://doi.org/10.1007/s10804-009-9082-y

World Health Organization. (2022). Mental health at work. https://www.who.int/news-room/fact-sheets/detail/mental-health-at-work

World Health Organization. (2022). Mental health: Strengthening our response. https://www.who.int/news-room/fact-sheets/detail/mental-health-strengthening-our-response

World Health Organization. (2025, September 2). Over a billion people living with mental health conditions — services require urgent scale-up [Press release and Mental Health Atlas 2024 data]. https://www.who.int/news/item/02-09-2025-over-a-billion-people-living-with-mental-health-conditions-services-require-urgent-scale-up