There are two main theories about the biological cause of depression and anxiety. The Serotonin Hypothesis, an older theory, states that a reduction in serotonin leads to an increased risk of depression. Serotonin is a neurotransmitter that influences one’s emotions, arousal levels, sleep, and memory. Factors that influence serotonin levels in the brain can trigger depressive symptoms for an individual.

A specific variant of the Serotonin Transporter Gene, named 5-HTTLPR, has a direct relationship with depression. People who inherit two short versions of the gene from their parents are much more likely to have depression than people who inherit two long versions (Fratelli et al., 2020). Depressive disorders also result from a combination of different genes. Genome-wide association studies (GWAS) identified multiple genetic combinations that may contribute to depression. Adoption studies indicate genetic influence on depression and anxiety, with those having a family history of depression being two to three times more likely to be diagnosed (Shadrina et al., 2018; Lamblin et al., 2017).

For adolescents in Generation Z, significant developmental changes in the body also contributes to the increased risk of depression and anxiety. During adolescence, large quantities of estrogen in girls and testosterone in boys are released, leading to significant hormonal fluctuations, especially for girls during the menstrual cycle (Albert and Newhouse, 2019). These fluctuations likely cause emotional instability in teenagers, causing depression and anxiety. This association is further proven by the significant increase in the likelihood of teenage girls developing major depressive disorders compared to boys, attributed to the hormonal fluctuations experienced by girls (Albert and Newhouse, 2019).

The Neurogenesis Theory provides a different explanation for a biological cause. This theory proposes that depression results from a reduction in neuron birth or the overall number of neurons in the hippocampus and neural network.

During adolescence, cessation occurs when excessive neuronal synapses in the brain are eliminated in a process called neural pruning (Centre for Clinical Interventions, 2023). Neural pruning induces disruptions in different areas of the brain, worsening adolescents’ ability to regulate emotions and leading to a higher risk of depression and anxiety (Blakemore, 2019).

HPA-axis hyperactivity is another cause of cessation. The HPA-axis is a system that deals with the fight-or-flight response during stressful situations. During this response, the adrenal glands secrete the hormone cortisol. When the HPA-axis is constantly activated, excessive amounts of cortisol cause apoptosis, or cell death, in the hippocampus. This leads to an abnormally small hippocampus, consequently heightening the chance of developing depression and anxiety.

Biological Approach to Treatment

To address the biological causes of depression and anxiety, Selective Serotonin Re-uptake Inhibitors (SSRIs) are commonly used as treatment. They inhibit the re-uptake process in neurotransmission, which leads to high serotonin levels in the synaptic cleft addressing the biological cause in the Serotonin Hypothesis. Additionally, SSRIs can stimulate the growth of neurons, thus also targeting the Neurogenesis Theory.

Unfortunately, SSRIs are not as effective as desired. Trials on people suffering from moderate to severe depression find that 20 to 40% of people taking a placebo pill and 40 to 60% of people taking SSRIs report improvements in mood in six to eight weeks. (“How Effective Are Antidepressants?”, 2020) Although this is a significant increase in percentage, there is still a significant portion of people who do not respond effectively to SSRI. Moreover, side effects of SSRI include headaches, joint pain, muscle aches, nausea, skin rashes, or diarrhea, causing harmful effects on the patient’s body (What Are the Real Risks of Antidepressants? - Harvard Health, 2021). This creates significant health problems for patients, bringing more stressors into their lives.

Additionally, medication for depression and anxiety is influenced by the placebo effect. The placebo effect contributes up to 75% of the drugs' observed effect, indicating its greater significance than the drugs' pharmacological effects (Irving & Guy, 1998). These outcomes raise doubts about the true effectiveness of SSRIs.

Cognitive Causes

Cognitive causes of depression and anxiety are cognitive distortions. One major cause of these distortions are stressful life events (Shapero et al., 2013). As mentioned previously, stressful events causing HPA-axis hyperactivity can lead to apoptosis in the hippocampus. As the hippocampus is responsible for memory encoding and retention, these events impair adolescents’ cognitive functions, leading to higher possibilities of emotion dysregulation. For instance, childhood trauma can lead to other cognitive distortions such as learned helplessness, making children pessimistic about their situations and inducing depression and anxiety (Guerry and Hastings, 2011).

Another cognitive cause of depression and anxiety is rumination. Rumination is a process people use to treat depressive events through repetitively thinking about the event’s causes and consequences. It contributes to cognitive distortions like negative thoughts, poor problem solving, biased information processing, and learned helplessness. Rumination can help people directly predict the emergence of depressive symptoms, the maintenance of existing symptoms, and reduced response to treatment (Ehring, 2021).

Cognitive Approach to Treatment

Cognitive Behavioral Therapy (CBT) is a treatment aimed to change an individual’s  thinking and behavioral patterns. A common form includes talk therapy where the therapist engages with the patient to address mental health issues. Cognitive therapies first identify negative thoughts and employ strategies to transform these thoughts into more positive and constructive ones. Behavioral therapies encourage patients to engage in healthy and rewarding activities to counteract depression. For anxiety disorders towards specific objects, exposure therapy is used to slowly expose patients to the object, gradually mitigating their fear of it.

CBT is widely used today for two major benefits. Cognitive distortions are often the root cause of mood disorders such as depression and anxiety. By decreasing the impact of various stressors on the patients, the therapy brings long term benefits to the patient. Another advantage of this therapy is its adaptability to different circumstances. CBT can be conducted both online and in-person, in individual, self-service, or group settings (Gotlib & Joormann, 2010). Thus, CBT is highly accessible to the public.

While CBT is proven highly effective, limitations exist. For online treatments, it is difficult for a therapist to precisely detect a patient’s minor reactions, potentially limiting the therapy’s effectiveness. This difficulty significantly increases the attrition rate in CBT programs, with an average of 32% aggregated from 16 studies. Reasons for participant withdrawal include time constrictions, family problems, and illnesses which increase pressure on these patients and make them more vulnerable to persistent depression (Schmidt et al., 2018)

Sociocultural Causes

With a continuously increasing population and limited opportunities, Generation Z faces intense competition. Most Generation Z are currently either in college or have entered the workforce. In the US, as of February 2024, 4.7% of recent college graduates are unemployed, and 40.8% of them are underemployed (The Labor Market, 2024). Due to a lack of experience in the workplace and financial crisis from low wages and student loans, Generation Z faces immense pressure during this transition, possibly contributing to their depression.

Additionally, Generation Z are more susceptible to pressures from social media platforms. While this could bring benefits such as an increase in social interactions and access to peer support, increased access to social media is linked to higher risks of depression, anxiety, and suicidal thoughts (Naslund et al., 2020). A range of factors including social comparison with peers, cyberbullying, online harassment, lack of in-person interactions, and privacy issues contribute to this phenomenon (Jinasena, 2014; Naslund et al., 2020). A meta-analysis of 13 studies shows that increased time, activity, engagement, and addiction to social media are positively correlated with symptoms of depression and anxiety (Keles, 2019).

Under a globalized society, Generation Z are becoming more politically and socially aware. Global issues, such as global warming and war conflict, make people less optimistic about the future, adding another layer of anxiety and worsening mental state. Additionally, during the earlier years of the COVID-19 pandemic, Generation Z suddenly lost the opportunity to physically go to school. With the absence of in-person classroom instruction, peer groups, academic support, exercise, and ability to access nature, people’s mental health severely declined during this period (Houghton et al., 2022; Schwartz et al., 2021).

Sociocultural Approach to Treatment

Internet-based interventions serve as a promising solution by sharing knowledge and raising awareness to prevent depression and anxiety in Generation Z. A meta-analysis of online interventions for adolescents after COVID-19 demonstrated a significant decrease in the risk of developing anxiety and depression, supporting its effectiveness (Fischer-Grote et al., 2024). This method can effectively spread knowledge about depression and anxiety prevention to a vast audience at a low cost (Iglhaut et al., 2024). It is especially suitable in the post COVID-19 world where transportation and offline meetings are limited. Moreover, as intervention programs are sometimes long-term projects, online programs make it significantly easier to monitor the conditions of participants regularly without commuting repetitively (Ye et al., 2014; Andersson and Titov, 2014). It also decreases the input required from participants, contributing to a further widespread impact.

On the other hand, it is important to note that only 22% of the global Generation Z population reported using digital mental health programs (Coe et al., 2023). This statistic suggests that this solution is still not widely accessible to all young people.

Internet-based interventions’ functions are supportive but not therapeutic. Depression and anxiety can be diagnosed without direct contact with the patient (Andersson and Titov, 2014). Thus, it remains difficult using Internet intervention programs as the main course of patient treatment for a patient.

Conclusion

This essay identifies major causes of depression and anxiety and evaluates the effectiveness and availability of different treatments. The variability in effectiveness of SSRIs coupled with its side effects complicates its application to every individual. The Cognitive Behavioral Therapy approach has been proven successful by multiple research studies and is highly flexible. Although the sociocultural approach of Internet-intervention programs yields promising results for awareness and symptom prevention, it cannot target people who have already developed symptoms, and a limited percentage of Generation Z uses these digital programs.

These methods can only solve a part of this issue individually. Providing comprehensive treatment and cure for Generation Z with depression and anxiety requires a combination of all three aspects.

For Generation Z from low-income families, many may not be able to receive the seemingly accessible treatments due to financial burden. Treating depression and anxiety among Generation Z remains a challenging task. Consequently, it is important for future research to focus on addressing the risk factors collectively so that more young people can be treated.

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