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Depression: An Epidemiological Perspective

Mental health conditions are typical in contemporary social systems, like the US, which has the highest rate of depression among developed countries. Hundreds of millions suffer from mental health disorders annually, and it is the leading cause of disability that contributes to the overall disease burden.

Depression is a common yet complex disease affecting around 320 million people globally, and over 700,000 people lose their lives each year. On a global scale, depression is the 4th leading cause of death among 15-29 year olds. Women are also more likely to experience depression, individuals with PTSD, those suffering from chronic illness, the elderly, and the transgender community. The probability for women to experience major depression at some point in their life is 1 in 3, and for men, that is 1 in 5. Nearly 50% of these individuals also have a diagnosed anxiety disorder. Ironically, 75% of patients being treated for depression had also suffered at least one traumatic experience during their childhood.

Severe depression affects 4% of the general population, and more than half of those with major depression do not respond to antidepressants, and 75% remain untreated.

Symptoms of depression include feelings of hopelessness, sadness, emptiness, anger, irritability, or frustration. Other symptoms are loss of motivation to engage in activities once enjoyed, changes in sleep and food habits, tiredness, restlessness, anxiety, suicidal thoughts, difficulty concentrating, and low self-efficacy.

Alexander Kaltenboeck MD states, “Depressive disorders are characterized by the prolonged presence of specific somatic and cognitive abnormalities in combination with sad, empty or irritable mood, or anhedonia” (2018). Is this neuroplasticity resulting in negative neuroplastic outcomes? A side note- Anhedonia is the inability to experience pleasure of any kind.

Depression also causes structural changes in the brain. In a recent study conducted on women with depression, there was a 13% reduction in the size of their hippocampus. A study conducted in 2008 found correlations between dysfunctions within the amygdala/ prefrontal cortex and the development of anhedonia, as well as dysfunctional emotional perceptions and regulation.

Some of the areas of the brain affected by depression are listed below:

• The Hippocampus develops two types of memories: declarative memories (retaining facts) and spatial relationships (memorizing a route to work). Also responsible for the perception of space.

• The Thalamus relays information from the prefrontal cortex to other brain regions. Also, sleep, consciousness, wakefulness learning, and memory play a role.

• The Amygdala plays a central role in processing emotions and emotional reactions related to fear.

• The Prefrontal Cortex affects personality, ability to plan, and behavior. The PFC has two parts: Medial PFC (mPFC), which is involved in self-reflection, and Lateral PFC (lPFC), which is involved in sensory processing and motor control.

Causes of Depression

It is believed that depression is caused by the interaction of biological, behavioral, environmental, and genetic factors that involve several processes. Depression can affect how a person feels, thinks, and behaves, and it is not the fault of the person suffering from it.

Depressive episodes can generally be traced back to high stress levels, but the causes are unknown, as many factors influence its development, and each person’s biochemistry, and experiences are unique.

Below is a list of causes of depression, according to doctors, psychologists and neuroscientists:

Chemical Imbalance: This theory has been around since the sixties and was believed to cause depression based on the brain's inability to regulate neurotransmitters like serotonin. Current evidence suggests that this is likely not the cause of depression, and it’s development may be more complex than just an imbalance of feel-good chemicals in the brain. Interestingly, people who take SSRIs for longer periods have lower serotonin levels, suggesting the brain becomes dependent and stops producing it on its own. Antidepressants may act as more of a bandaid for some instead of a cure.

Inflammation: According to research, Major Depressive Disorder is associated with a 30% increase in inflammation in the brain which may drive depressive symptoms like low mood, loss of appetite, and insomnia. Inflammation is now considered a major link in the development of severe depression.

Medications: Certain medications can cause depression, such as corticosteroids, beta-blockers, Benzodiazepines, drugs that treat Parkinson's disease, and drugs that manipulate hormones, such as birth control and those used to treat menopause. The list continues with stimulant drugs, anticonvulsants, proton pump inhibitors, antibiotics, statins, and thyroid and allergy medications also increasing the risk.

Genetics: Depression is 50% determined by your genes, and having a grandparent or parent with depression doubles your chances of having depression.

Personality: According to research, some personality traits are associated with an increased risk and development of depression and other mood disorders. Some of these personality traits include:

• Learned Helplessness- another name for this is external locus of control, and people who adopt this behavior see themselves as helpless to circumstances that occur in their life and environment.

• Negative Thinking- 95% of our thoughts are repetitive, and depressed people tend to ruminate on the same negative thoughts that produce symptoms of depression.

• Emotionally and Physically Drained- Depression depletes the brain and body and leaves the individual in a state of malaise, lacking the energy to change their thoughts and lifestyle choices but staying motivated to make the same ones that increase depressive symptoms.

• Biased Memory- Depression is associated with a higher recall of negative events, leading to rumination and increased heightened responses to seeking negative experiences to confirm biases.

Physical Health: Suffering from a chronic and debilitating illness can increase the chances of developing depression. This is due to the often debilitating discomfort and diminished quality of life that accompanies chronic illnesses like MS, cancer, IBD, and diabetes. Certain types of illnesses can also cause depression, such as liver disease and thyroid disorders.

Sex: Females are almost twice as likely to develop depression than men, and several factors contribute to this statistic. Fluctuations in sex hormones increase the chances of women experiencing depressive symptoms during certain stages in their monthly menstrual cycle, and interestingly, the risk of depression decreases after menopause.

Some factors that influence female depression are listed below:

• Sexual objectification of women

• Discrimination

• The menstrual cycle due to fluctuations in sex hormones

• Patriarchal restrictions on autonomy

• Physical and sexual violence

Environment: Our environments shape our lifestyle choices, habits, moods, attitudes, and behaviors, and for individuals at higher risk, certain locations and times of the year can increase the chances of developing Seasonal Affective Disorder (SAD). An example is the high rates of depression among Alaskans who experience “Alaska Darkness” during the winter months, where some areas do not see the sun for 67 days out of the year. 43.1% of Alaskans struggle with depression, as opposed to 23% of people in Colorado and 25% in New Zealand.

Nutrition: Nutrient deficiencies are thought to play a role in depression. Some nutrients studied and found to reduce depressive symptoms include zinc, omega 3’s, folate, olive oil, tea, fruit, vegetables, whole grains, and low-fat dairy. However, diets high in red meat/ processed meats, refined grains, sugar, and butter were associated with depression.

The gut microbiome is believed to influence depression, and individuals with dysbiosis or an imbalance in bad vs good gut bacteria have higher levels of systemic inflammation, which increases the risk of developing depression. Some gut bacteria strains are currently being researched and utilized for their effects on reducing depressive symptoms in some patients with depression.

Trauma: According to Gabor Mate, MD, trauma can be defined as a “psychic wound that imprints on your nervous system, psyche, and physiology”.

Most people on a global scale have experienced trauma at some point in their life. Trauma can lead to depression as well as PTSD. 1 in 4 girls and 1 in 3 women experience sexual abuse; for boys, that is 1 in 13, and for men, 1 in 4.

A study showed that childhood trauma before the age of 7- that includes sexual, physical, or emotional abuse — had less success with antidepressant treatments.

Trauma during childhood can result in the development of negative schemas (opinions) about one’s self, as well as automatic negative thinking.

Addiction: Around 1/3 of people with clinical depression also have a substance use disorder (SUD). Adults who suffered sexual abuse as children are 1.5 times more likely to use illicit drugs.

There is a strong connection between addiction, trauma, and depression, which creates a vicious trifecta and perpetuating cycle reinforced through negative self-thinking. This is due to neuroplasticity and how the brain changes when we learn something new, and the more a person engages in negative thoughts, such as those that drive addiction or depression, the stronger the neural pathways in the brain become, reinforcing the craving and seeking the stimulus.

Risk Factors

There are many risk factors for depression, including a person’s-

Sex: Women are twice as likely as men to have depression. This is due to hormonal changes from the menstrual cycle and the high prevalence of sexual and physical abuse against women and girls, leading to trauma and, ultimately, depression. Post partum depression is type of depression that affects women who have just given birth and is believed to be influenced by hormones and genetic factors.

Genetics: An individual with a family member, such as a sibling or parent who has a mental health disorder, like Bipolar disorder has a 50% chance of developing one, too.

Socioeconomic status: Lower socioeconomic status has been associated with higher rates of depression among adults.

Vitamin D deficiency: Many people suffering from depression also have a vitamin D deficiency, although research findings are mixed.

Gender identity: Gender-diverse people have a fourfold increased risk of developing depression. Based on a US Transgender survey, 40% of participants said they had attempted suicide at some point in their life. Another study concluded that over 2 in 3 transgender youth suffered from Major Depressive Disorder.

Addictions: Addictive behaviors are vast and can range from being addicted to heroin or healthy food, exercise, sex, food, marijuana, alcohol, and other substances. Substance use and childhood abuse is strongly linked. Abuse can lead to PTSD that leads to addiction, and 28% of those diagnosed with PTSD also have an addiction, and another 35% have a serious addiction to a behavior or substance. Roughly 50% of individuals seeking mental health services are affected directly or indirectly by addiction.

Support systems: Poor social connections and relationships are linked to depression. A study conducted in 2023 on the effects of isolation during the pandemic found that 4 in 10 adults experienced loneliness and isolation. Low social support is also linked to addictions like alcoholism, cardiovascular disease, and suicide.

Health status: illnesses increase the chance of developing depression and anxiety. Chronic Illness adds an additional 25-30% increased risk of developing depression. People with mental conditions such as Bipolar Disorder also suffer from depressive episodes called “lows.”

Age: Older adults are at an increased risk for depression, and in the US, 15% of adults aged 60 and over suffer from a chronic mental health disorder.

Race: Depression rates have risen across all races, but those with the highest rates are among populations identifying as more than one race. People of color face disparities that often lead to a lack of diagnosis and treatment. In fact, one study showed that for patients seeking medical care, among the white community, 87% received care whereas 80% of the Asian population did not. That noted, even the lower rates of depression among Black people might indicate more disparities within the US healthcare system and inaccurate stats.

Environment: A person’s environment plays a role in the risk factors associated with depression. This can be examined using the social determinants of health model, which lists influencing factors that explain behaviors, beliefs, and attitudes within communities and regions. Environmental causes of depression can also include a person’s socioeconomic status, zip code, neighborhood, interpersonal relationships, employment status, natural disasters & outbreaks, education, marital status, food availability, etc.


Anti-Depressants- Antidepressants aim to increase and alter the distribution of neurotransmitters, which are chemical messengers in the brain. By doing so, they increase positive emotions and decrease negative ones. Based on a study conducted to determine the efficacy of antidepressants, the results revealed that between 20-40% of people prescribed a placebo saw an improvement in their mood within 8 weeks, and the rate was 40-60% for those prescribed an antidepressant. This means antidepressants are 20% more effective than not taking an antidepressant. Antidepressants can be life-saving for some, and for others, can increase symptoms of depression like suicidal ideation. Antidepressants also seem to result in plateaus in which the patient requires a stronger dosage due to tolerance build-up. According to health professionals, antidepressants may be more effective for short-term relief than for long-term treatment.

Mantrum Repetition Therapy- MRP is the repetition of a mantra that helps calm the mind by eliminating thoughts and the negative feedback loops that accompany them in individuals with depression and other mental disorders. MRP therapy has proven beneficial in treating veterans with PTSD, depression, anxiety, and general mood disorders. “MRP appears efficacious in reducing hyperarousal, and thereby impacting other PTSD symptom clusters, as one pathway to facilitating recovery” (Crawford, 2019). You can do MRP anywhere at any time by repeating a mantra that works for you.

Psychological Interventions- These interventions require the aid of a professional with specified credentials and are usually most effective when used in tandem with antidepressants. Some examples of these interventions include CBT, DBT, psychodynamic therapy, and interpersonal therapy. These therapies are proven to reduce symptoms associated with anxiety and depression.

Psychedelic Therapy- The recent increase in studies on the efficacy of using psychedelics to treat depression is showing promising results. Compounds such as psilocybin have been shown to reduce symptoms of depression up to one year post-treatment. Other psychedelic compounds being researched to treat depression include ketamine, MDMA, LSD, DMT, and mescaline.

Meditation- Study results confirm that a person’s ability to regulate their emotional responses plays a substantial role in mediating responses relating to mindfulness vs rumination. This suggests that meditation helps rewire thoughts via neural circuits or pathways in some areas of the brain associated with depression, such as the prefrontal cortex and limbic system. Meditation can help us get to where we notice our thoughts and the emotions connected to them so we can process them in healthy ways.

Other Tips To Support Mental Health

Exercise, nutrition, and possible supplementation with the right herbs or nutraceuticals can support mental health and recovery from depression. Acupuncture has been considered a supportive practice for depression, as well as yoga, and reflexology. Light therapy can help individuals suffering from Seasonal Affective Disorder (SAD). A community support group can also be of benefit in the treatment of depression due to the sense of connection and community it can instill, sharing with others similar stories, experiences, and histories that led to the development of their depression.


Depression is a complex disease that can affect anyone and is never the fault of the individual. Many factors can increase a person’s risk of developing symptoms of depression, like chronic stress, PTSD, genetics, environment, sex, race, and health status.

People can recover from depression, which is often spontaneous, requiring no treatment at all. However, the more depressive episodes one has, the more likely one is to relapse.

There are many therapies and treatments for depression, although we still don’t fully understand its causes and how best to treat it at the individual level. Each person is unique in their biochemical makeup, and with that, the most critical consideration is finding the best support and therapy that works for the person who is struggling to get better but lacking the proper resources and support.





  4. Kaltenboeck, A., & Harmer, C. (2018). The neuroscience of depressive disorders: A brief review of the past and some considerations about the future. Brain and Neuroscience Advances.















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  20. Bailey, R. K., Mokonogho, J., & Kumar, A. (2019). Racial and ethnic differences in depression: current perspectives. Neuropsychiatric disease and treatment, 15, 603–609.






  26. Crawford, J. N., Talkovsky, A. M., Bormann, J. E., & Lang, A. J. (2019). Targeting hyperarousal: Mantram Repetition Program for PTSD in US veterans. European journal of psychotraumatology, 10(1), 1665768.


  28. Parmentier, F. B. R., García-Toro, M., García-Campayo, J., Yañez, A. M., Andrés, P., & Gili, M. (2019). Mindfulness and Symptoms of Depression and Anxiety in the General Population: The Mediating Roles of Worry, Rumination, Reappraisal and Suppression. Frontiers in psychology, 10, 506.



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