Is depression genetic or environmentally influenced? This question has been challenging to answer for many years, with researchers only managing to scratch the surface. However, advances in research have opened the door to learning how a wide array of environmental factors influence depression. With each new discovery, many questions arise about the nature of depression and environmental factors.
Read on to understand the role of environmental risk factors, and then learn about several specific factors and their effects in more detail.
When examining the potential causes for depression, the following question is often raised: Which is the more substantial influence on depression, genetic or environmental factors? Studies estimate that between 37-48% of vulnerability for depression stems from genetics, leaving the environment to account for potentially more than half of the remaining influence.
Much of the current understanding of this interaction derives from epigenetic research, the study of how external factors impact genetic expression without changing the DNA sequence itself. Epigenetic studies have revealed that the dynamic interaction between environmental factors and genetic sensitivity is significant enough to predict major depressive disorders risk and onset. Evidence suggests these interactions reflect causal mechanisms, each involving the combined impact of multiple and overlapping gene effects.
Timing appears to be an essential aspect of environmental influence, indicating that some combinations of age-specific environmental and genetic factors may have somewhat identifiable risk potential. Some evidence suggests that environmental impacts have more effect in younger years, with genetics playing a stronger role in adulthood. This effect can be seen when examining the influence of early life stress. Early life stress is known to harm the brain, impacting its plasticity during a critical period of development when it is susceptible to adverse experiences.
For individuals with early stress exposure, the harmful effect of a stressful environment can be two-fold.
Environmental factors significantly affect the timing, duration, and long-term outcomes of depressive disorders. Researchers are looking more deeply at the multitude of environmental factors with meaningful ties to depression.
Preterm birth and poor fetal growth have been associated with depression, highlighting the potential long-term effects of prenatal distress or challenging pregnancy conditions. These factors also impact depression risk independently of each other. One study revealed a 2.75-fold increase in risk with preterm birth, and another found the risk only affected girls. Poor fetal growth was less impactful but had a stronger association as the gestational age increased.
Other prenatal impacts have been linked with an increased risk of depression. One animal study showed that conditions mimicking infection during gestation resulted in the offspring displaying depression-like behaviors. Human studies have reported connections between second trimester maternal infection and increased reports of adolescent depression in the affected offspring.
Parental depression interferes with the engaging and supportive environment needed for healthy child development, with maternal depression showing the strongest impact. This connection is so robust that it is observed worldwide, deemed a global threat to children’s health. Maternal depression can produce other environmental effects such as a disorganized home, disrupted parent-child relationships, and economic hardship. More research may be required to clarify the multifaceted impact of maternal depression.
Research studies affirm that childhood bullying is one of the most potent risk factors for depression across the lifespan. Research findings suggest that the impact of bullying may be time-sensitive due to its connections with both short-term and persistent courses of childhood depression. Weaker links have been observed with adolescent and adult depression, suggesting these impacts may result from genetic vulnerabilities rather than the immediate reactions to bullying incidents.
The time children are most vulnerable to depression following the death of a parent is during the first two years of bereavement. Children ages twelve and younger had the highest incidence of depression, revealing a greater sensitivity to interpersonal loss during this age span.
While not always readily considered as a potential cause, many physical environmental factors can increase the risk of depression.
Airborne Pollution: Exposure to airborne pollutants may negatively influence neural plasticity, the ability of the nervous system to adapt when faced with positive and negative stimuli. This capability is often altered in mental conditions such as depression.
Noise Pollution: Noise pollution has been linked with sleep disruption, a significant symptom of depression. Depression has also been associated with noise sensitivity as well as exposure to traffic, aircraft, or railway noise.
Natural Disasters: Economic losses, psychological trauma, and other negative impacts from natural disasters contribute to an understandably distressing environment. Depressive symptoms may appear in the short term for some, but long-term depression and increased suicide risk have also been linked with these events. The prevalence of depression among adults and children exposed to natural disasters ranges widely, with the most common risk factors being prior trauma, fear, and bereavement during the disaster.
Researchers have learned much about the importance of environmental factors in the development of depression. They represent the majority of potential risk factors for depression across all age groups. While the associations themselves are not all well-understood, exploring these factors helps to clarify the complex picture of depression.