Depression 101: Prevalence, Burden, and the Role of Exercis Darragh O’Sullivan.

Health Disclaimer

This blog provides general information about depression and exercise which should not be used as a substitute for professional medical advice.  If you or any others are experiencing depression, you should seek treatment advice from your doctor or a trained mental health clinician.

What is Depression?

Unlike anxiety, depression can be difficult to define due to differences between the various depressive disorders and inter-individual differences in the experience of those disorders.  An individual’s experience of depression can vary depending on the type of depressive disorder they have developed, such as major depressive disorder (major depression), persistent depressive disorder (dysthymia), seasonal affective disorder (seasonal depression), or peripartum depression (postpartum depression); despite these differences, the hallmark symptoms of any depression remain consistent: 1) increased depressed mood and 2) a loss of interest or pleasure.  Major depressive disorder is one of the most common psychological disorders and is likely what you think of when you hear ‘depression’.  It is an episodic disorder, meaning that the depression occurs in episodes and then clears; recurring depressive episodes are common, with evidence suggesting that each depressive episode increases the risk of experiencing another by approximately 16%.  Along with the hallmark symptoms of depression, individuals with major depressive disorder can also suffer from sleep disturbances, excessive weight loss or gain, feelings of restlessness or lethargy, excessive tiredness, difficulty concentrating, excessive worry or guilt, and thoughts of suicide.  For a diagnosis of major depressive disorder, at least one hallmark symptom and five other symptoms must be present for most of the day, every day for at least two weeks; symptoms must cause significant distress or impairment; and symptoms should not be caused by a substance, another medical condition, a psychotic disorder (e.g., schizophrenia), or a manic episode (e.g., bipolar depression).

Prevalence of Depression

Like many other mental and physical illnesses, prevalence rates for depression vary depending on numerous factors including age, gender, socioeconomic background, health status, and country of residence.  Evidence suggests that 1) approximately 1-17% of people (varying based on country of residence) suffer from major depressive disorder at least once in their lifetime (e.g., 16.9% in the US; 8.3% in Canada; 1.0% in the Czech Republic), 2) approximately 280 million people worldwide are currently affected by depression, 3) women are twice as likely to suffer from any form of clinical depression compared to men, and 4) people with chronic health conditions (e.g., cancer, multiple sclerosis, Parkinson’s disease) are at greater risk for depression compared to those who are otherwise healthy.

Age-of-onset of Depression

Most mental health disorders (including anxiety disorders) typically first develop during adolescence; however, depressive disorders more commonly develop in adulthood.  The median age-of-onset of a first major depressive episode is usually between the ages of 22 and 30; this is relatively consistent, regardless of the population.  Although prevalence rates for depressive disorders are highest among elderly adults, the typical age-of-onset of the first major depressive episode suggests that young adulthood is a critical period for 1) reducing the risk of first developing depression, 2) providing early treatment to those who have already developed depression, and 3) providing long-term strategies to those who are receiving or have previously received treatment for depression to reduce the risk of recurrence of depression upon cessation of treatment and later in life.

The Burden of Depression

The burden of depression extends far further than its primary symptoms.  For example, having depression is associated with cardiovascular disease, Alzheimer’s disease, social dysfunction, and other mental illnesses including anxiety; in fact, people who suffer from generalized anxiety disorder more often than not also have major depressive disorder, intensifying the symptoms and increasing the difficulty of treating both the anxiety and depression.  Depression is also the main risk factor for attempted suicide (another major risk factor is substance abuse); consequently, reducing the risk of onset of depression and adequately treating those who have already developed depression would likely significantly reduce the prevalence of suicide attempts.  Depression is also a major economic burden, with treatment costing €118 billion per year in Europe, making depression Europe’s most expensive brain disorder.  The World Health Organisation have projected that depression will be the leading cause of death and disability by 2030.

Exercise and Depression: Does it Work?

In short, yes (with important caveats).  Systematic reviews and meta-analyses of randomized controlled trials suggest that both aerobic and resistance exercise training interventions can induce similar moderate reductions in depressive symptoms.  An important caveat to consider when interpreting these findings is that the participants in most (but not all) of these studies were 1) novice exercisers and 2) not clinically depressed.  Still, a recent review of exercise interventions for depression among clinically depressed samples found that, overall, exercise interventions had large antidepressant effects.  The few studies that have compared the antidepressant effects of exercise interventions to those of traditional treatments such as antidepressant medications and psychotherapies have found no statistically significant differences between exercise interventions and the traditional treatments.  The experimental evidence for the antidepressant effects of exercise is also supported by evidence from large-scale epidemiological studies which generally suggest that people who are more physically active also have lower depressive symptoms. 

Our research group in the Physical Education and Sport Sciences Department at the University of Limerick is currently largely focused on the effects of resistance exercise training on mental health outcomes.  We have recently found larger than usual reductions in depressive symptoms among young adults following an eight-week resistance exercise training intervention and even larger reductions among those with symptoms indicative of subclinical major depressive disorder.  We are currently planning on replicating and expanding on these findings with another randomized controlled trial of young adult women, a particularly at-risk group for elevated depressive symptoms.

Bottom-line Role of Exercise in Treating Depression

Exercise is a promising tool that may be used as an alternative or augmentative treatment for depression.  Given the complexity of mental illnesses, dichotomizing the treatment of depression is likely unhelpful.  Many who suffer from depression may benefit from combining the available treatments.



Darragh O’Sullivan is a PhD Research Student in the Physical Education and Sport Sciences Department at the University of Limerick.  Darragh graduated from his undergraduate degree in Sport and Exercise Sciences in 2021 and is now completing his PhD research under the supervision of Dr. Matthew Herring, Dr. Mark Lyons, and Dr. Brett Gordon.  Darragh has research interests in the influence of exercise, general physical activity, and sedentary behaviors on mental health outcomes; his PhD research focuses on the effects of resistance exercise training on anxiety and depressive symptoms among young adults.

Contact: Twitter: @Darragh_Sully  LinkedIn: darraghsully

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