The Link Between Stress and Depression

Understanding the connection could promote greater resilience.

• Stress is correlated with depression.

• Correlation does not equal causation.

• How can we really know whether stress makes us depressed?

Stress gets blamed for a lot of things. Did you gain a few pounds? Blame stress. Say something you regret. Blame stress. But what about something more serious like major depressive disorder? Stress often gets the blame for serious mental illness, but we know that our genetics play a role as well. Depression afflicts an estimated 280 million people worldwide, many of whom would point to stress as a contributing factor to their depression.

Is it possible to tease apart the complex causes of disorders like major depressive disorder? Researchers have tried to do so, with limited success. Let's highlight some research that has benefited our understanding of this.

Do stressful life events cause major depression? Answering this question comes with several challenges. One of them is the chicken-or-egg question: how do we know that stress causes depression? Or whether someone’s depressive mood and behavior caused them stress?

One way to address this is through a prospective, longitudinal study in which stress and depression are measured in the same people over the years. This allows us to determine which came first, the stress or the depression.

To address this, researchers asked over 2,000 female twins about their stressful life experiences and symptoms of depression at three different times over about five years. Stressful life events included divorce, the death of a loved one, and job loss, among other events. The researchers took note of the timing of both the stressful event and the onset of the depression symptoms.

Their findings should come as no surprise: Stressful events often lead to the onset of depressive symptoms. When those who reported depression were asked whether something stressful happened to cause the depression or whether it came out of the blue, 85 percent said that the stressful event came first. None of them reported that depression came before the stressful experience.

Next, the researchers looked at the characteristics of the stressful events. At the risk of blaming the victim, events such as divorce could be partly due to the depressive nature of the individual. By contrast, events such as the death of a loved one should be independent of the depressive nature of the individual. Researchers found that even these independent stressful events, in which the individual had no role, led to the onset of depressive symptoms.

The researchers next took advantage of the fact that their participants were twins. This allows for the assessment of the impact of genetics on the stress-depression relationship. Monozygotic (identical) twins share 100 percent of their genes. Examining the relationship between stress and depression in these twins effectively controlled for the effects of genetics on the development of depression.

Within these monozygotic twin pairs, researchers found that stressful life events predicted the onset of depressive symptoms. These findings provide strong support for the idea that stressful life events—even those we have no control over—can lead to the onset of major depression regardless of our genetic makeup.

It's not all doom and gloom, however. The good news is that of the over 2,000 women tested in the study over five years, only about 300 (7 percent) of them developed major depressive disorder. What are the characteristics of these 1,700 women who did not develop depression? The answer to this question may allow us to promote resilience to lessen the negative effects of depression.

Tony W. Buchanan, Ph.D. - Website -

References

Institute of Health Metrics and Evaluation. Global Health Data Exchange (GHDx).

Kendler, K. S., Karkowski, L. M., & Prescott, C. A. (1999). Causal relationship between stressful life events and the onset of major depression. American Journal of Psychiatry, 156(6), 837–841.