• Amanda Metskas

Understanding the two most common mental health problems in the world


Chances are, your life has been impacted by anxiety disorders or depression, either through your direct experience or through the impact they have had on your loved ones. Anxiety and depression are the two most common mental health conditions in the world, but they are frequently misunderstood.


In this data-based essay, we aim to help you better understand anxiety and depression, as well as the hidden links between them. By improving your understanding of these disorders, you may find it easier to recognize anxiety and depression in yourself and be more effective at supporting people in your life who experience these conditions. This infographic summarizes some of our interesting findings about the differences and similarities between anxiety and depression (click here to see the infographic at full size).



The scale of both anxiety and depression is vast: the World Health Organization estimates that 301 million people worldwide suffer from an anxiety disorder, and 280 million people worldwide suffer from depression. Worldwide, depression ranks as the second largest cause of disability, and anxiety ranks eighth, according to analyses of the most recent Global Burden of Disease study. And yet, despite their prevalence and severe impacts, humanity’s scientific understanding has a substantial way to go to fully understand and highly reliably treat these conditions. Improved treatment and management techniques could make a huge difference in the quality of life of hundreds of millions of people around the world. These astounding statistics have motivated us to run our own studies investigating how these conditions work and how they relate to each other. This article will explain what we found!



Overlapping Disorders


A major obstacle to understanding anxiety and depression is that they often go together - many people who experience one also experience the other. Approximately 45% of people who experience a depressive disorder in their lifetime also experience an anxiety disorder, and these often occur during the same timeframe. Among people with Generalized Anxiety Disorder, about 43% of them will also experience depression in their lifetime. In one of our own studies, we found that commonly used measures of anxiety and depression (the GAD7 and PHQ9 scales) had shockingly high correlations (r=0.82). These strong links between anxiety and depression can make it more difficult to disentangle how each of these disorders works and make it more difficult for a person with anxiety and depression to effectively manage their conditions. Some people even think they have an anxiety disorder when it's more accurate to say they have a depressive disorder or the reverse.


The co-occurrence of anxiety and depression is a bit puzzling because they almost seem like opposites when experienced in the moment. A high level of anxiety often feels like being “wound up” – muscle tension, rapid heart rate, and chest tightness are among the most common physical symptoms. People experiencing anxiety may have a nervous energy that makes it difficult for them to relax, even if there is nothing they can practically do to address whatever is making them anxious. Depression, on the other hand, often feels like struggling to muster energy or motivation to care about things enough to take any action at all. Doing things, including things that a person ordinarily would find pleasurable, can feel pointless.


Yet, despite these contrasts, there are a number of overlapping symptoms that characterize both anxiety and depression - difficulty with sleep, gastrointestinal symptoms and/or struggles with eating, restlessness, inability to concentrate, irritability, and feeling tired all are symptoms connected to both anxiety and depression. These symptoms are also often used as part of the diagnostic criteria for the two disorders - each of them appears on the commonly used depression scale known as the PHQ-9 or the commonly used scale for Generalized Anxiety Disorder known as the GAD-7.


Mental health issues are diagnosed and defined in terms of constellations of symptoms, so the prevalence of these overlapping symptoms may be part of the explanation for the overlap in diagnoses of the two disorders. But that doesn’t seem to capture the whole story. In addition to the overlapping symptoms, many people simultaneously experience symptoms that are unique to anxiety and symptoms that are unique to depression.



Distinct Disorders


In order to better understand anxiety, depression, and the relationship between them, we asked over 500 people about their beliefs, experiences, personality, and behaviors. We analyzed the relationships between their answers to those questions and scales for measuring depression and anxiety levels (from which we carefully removed any overlapping symptoms). Our measure of anxiety only asked about anxiety-specific symptoms, and our measure of depression asked only about depression-specific symptoms. The questions we used are listed in the appendix to this article. By running a regression that predicted people's answers to each question (using each person's anxiety level and depression level simultaneously to make the predictions), we were able to divide all the questions we asked into four groups:


  1. those whose answers are predicted by both depression and anxiety

  2. those whose answers are only predicted by depression (i.e., anxiety is not a useful predictor when you know someone's depression level)

  3. those whose answers are only predicted by anxiety (i.e., depression is not a useful predictor when you know someone's anxiety level)

  4. those whose answers are predicted by neither depression nor anxiety


Examining the pattern of overlap between depression and anxiety provides some insights into how these extremely common disorders are related to each other and also how they are distinct. The infographic above summarizes some of our interesting findings about the differences and similarities between anxiety and depression (click here to see the infographic at full size).


Anxiety is focused on anticipating potential bad events, chronic worrying, and disliking uncertainty. The anxious person tends to have a sense that something could go wrong at any moment, and they are on alert for it.


Depression is focused on a sense of meaninglessness or hopelessness and a low opinion of oneself. The depressed person has a sense that something is wrong with them or with the world, and they feel that whatever is wrong is not going to change.


Here’s one way of summarizing this distinction: anxiety is about anticipating the possibility of bad things occurring, whereas depression is about the feeling that one will not experience (or create) good, meaningful, or valuable things.



Common Signatures with Subtle Distinctions

Some of the signature symptoms of these two disorders are similar, despite being generated by different processes. This similarity can make it difficult for individuals to identify what is causing their psychological distress. Here are a few key examples:


  • Repetitive negative thoughts - Both anxiety and depression involve repetitive thought patterns. In anxiety, that thought pattern is worry, often in the form of “what if” scenarios about possible bad things that could happen. In depression, that thought pattern is rumination, characterized by negative self-talk about one’s failings and past mistakes or despairing thoughts about the hopelessness or meaninglessness of the future or past. In both cases, those thought processes make it difficult for a person to focus on other things, and people get stuck in those thoughts and have trouble turning them off.


  • Fatigue - Both anxiety and depression commonly have fatigue as a symptom, but that symptom may have different causes in the two disorders. Both anxious and depressed people tend to feel tired and like their sleep isn’t restful, but only anxiety is associated with not sleeping enough hours. For anxious people, fatigue seems related to being unable to sleep and also possibly to the anxious state of being “on alert,” taxing the body and mind. We previously conducted a more in-depth analysis of fatigue and the relationship between anxiety and fatigue that shows that reducing anxiety in the moment reduces fatigue in the moment. For depressed people, fatigue isn’t typically caused by not sleeping enough hours - it seems more related to the lack of energy and motivation that characterizes the experience of depression itself. Sometimes depressed people even oversleep.


  • Avoidance behavior - Both anxiety and depression are associated with avoidance behaviors like canceling plans and having a hard time getting things done. Anxiety-driven avoidance behavior is typically an unhealthy coping mechanism that reduces the experience of anxiety in the moment by avoiding the situation that provokes the anxious feelings (e.g., avoiding a party because socializing makes you feel stressed out). Depression-driven avoidance behavior is typically due to feeling like whatever is being avoided isn’t worth doing or is pointless, or simply not having the energy or motivation to do things (e.g., avoiding a party because you feel exhausted and assume that nobody cares if you go anyway).


  • Pessimistic beliefs - Both anxiety and depression are associated with certain pessimistic beliefs, such as beliefs about the world being unsafe or that when one thing goes wrong, other things will go wrong too. For anxious people, pessimistic beliefs tend to focus more specifically on potential risks and threats. Depressed people tend to have a broader range of pessimistic beliefs that are part of an overall negative outlook.


  • Beliefs about the self - Both anxiety and depression are associated with some negative beliefs about the self, such as lacking confidence about accomplishing goals and thinking you look ugly or stupid. In anxiety, these beliefs tend to be related to fears, especially social fears about performing poorly, letting others down, or being judged by other people. Depressed people tend to have a broader set of low self-image beliefs and negative self-talk - in addition to anticipating the judgments of others, depressed people judge themselves very harshly.


  • Cognitive distortions - In one of our studies, we investigated the link between mental health and common distortions in thinking, finding that (based on self-report of how often people engage in these patterns of thinking) some such distortions are associated with both anxiety and depression, such as overgeneralizing, filtering, and labeling. Other distortions, such as catastrophizing and jumping to conclusions, were associated with anxiety but not depression (when controlling for anxiety). Still, others, such as emotional reasoning and blaming, were associated with depression but not anxiety (when controlling for depression). These results are summarized in the diagram below!



By comparing the overlapping and non-overlapping sets of symptoms, we can get a clearer picture of how the two distinct underlying processes of anxiety and depression produce symptoms that can be difficult to distinguish, especially when some people experience both conditions.



Intertwined Effects


In addition to difficulty distinguishing causes when anxiety and depression co-occur, the two disorders can create feedback effects that amplify each other. When anxiety and depression team up and generate the symptoms described above, those symptoms can feel all the more overwhelming and difficult to escape. For example, someone struggling with motivation and energy during a depressive episode may then start to experience anxiety about potential negative consequences that could occur due to their difficulty accomplishing tasks while depressed. For instance, they might fear that their depression will impact their job and financial security or their important relationships. This anxiety could then further encourage avoidance behavior on tasks that feel high stakes, which reinforces the same avoidance behavior that being in a depressed state encourages. Similarly, someone who experiences a high degree of anxiety may start avoiding many of the things in their life that they enjoy (in an attempt to avoid anxious feelings). This could lead to social isolation and a lack of joy and meaning in life, leading to subsequent depression.



A final reason that anxiety and depression are linked is that they can both be consequences of other factors. For instance, someone who grows up in poverty may be at increased risk for depression (due to having difficulty pursuing meaningful goals) and anxiety (due to elevated risk levels in their environment). It may also be possible that some genes code for an increased likelihood of getting both depression and anxiety. Factors like these can link anxiety and depression together, making them even more correlated than they would otherwise be.


If you are dealing with both depression and anxiety, being able to identify the differences between the repetitive thoughts or negative self-beliefs generated by depression and anxiety may help you more effectively challenge these beliefs or disengage from these thought patterns. For example, if you struggle with avoidance, being able to identify whether your avoidance behavior is motivated by anxiety about the particular thing you are avoiding or motivated by a generally depressed state may help you develop more effective strategies for overcoming avoidance when you need to.


Our long-term goal for this research is to identify more targeted interventions to help people dealing with depression, an anxiety disorder, or both. Particularly, if anxiety and depression are both present, identifying whether one of the two conditions is more primary would help target treatment towards the primary issue. Additionally, helping people dealing with both anxiety and depression understand the feedback effects between their two conditions may help people to begin breaking those cycles.


Look out for future findings from this research in our newsletter!




Appendix: Questions we used to measure anxiety and depression


In this research, to measure anxiety and depression, we used the following questions taken from two commonly used scales for diagnosing depression and anxiety. Each of these scales has other questions that we did not include in this analysis because they relate to symptoms that are highly overlapping between depression and anxiety.


The answer options for both of these scales are four-point scales with the options labeled: Not at all, Several days, More than half the days, Nearly every day.

Questions that we used from the PHQ-9 for diagnosing Depression:


Over the last two weeks, how often have you been bothered by the following:

  • Little interest or pleasure in doing things?

  • Feeling down, depressed, or hopeless?

  • Feeling bad about yourself — or that you are a failure or have let yourself or your family down?

  • Thoughts that you would be better off dead, or thoughts of hurting yourself in some way?

Questions that we used from the GAD-7 for diagnosing Generalized Anxiety Disorder:


Over the last two weeks, how often have you been bothered by the following:

  • Feeling nervous, anxious, or on edge?

  • Not being able to stop or control worrying?

  • Worrying too much about different things?

  • Trouble relaxing?

  • Feeling afraid, as if something awful might happen?