We all know people who are able to roll with life's punches, while for others, every misfortune is a jab straight to the gut. Research examining this issue has found that although most people require significant adversity to become depressed - the death of a loved one, say, or getting fired - roughly 30% of people with first-time depression and 60% of people with a history of depression develop the disorder following relatively minor misfortunes. But no one knew why.
Now, a new study led by UCLA researchers suggests that people become depressed more easily following minor life stress, in part because they have experienced early life adversity or prior depressive episodes, both of which may make people more sensitive to later life stress.
George Slavich, an assistant professor at the UCLA Cousins Centre for Psychoneuroimmunology, and colleagues assessed individuals' experiences with early adversity, clinical depression and recent life stress. Slavich found that individuals who experienced an early parental loss or separation and people who had more lifetime episodes of depression became depressed, following lower levels of life stress than those who didn't have these predisposing factors.
The study appears in the Journal of Psychiatric Research.
"We have known for a long time that some people are more likely to experience mental and physical health problems than others," Slavich said. "For example, while some people get depressed following a relationship breakup, others do not. In this study, we aimed to identify factors that are associated with this phenomenon and to examine whether increased sensitivity to stress might be playing a role."
The researchers recruited 100 individuals with depression, 26 men and 74 women, and interviewed them extensively to determine what types of adversity they were exposed to when they were young, how many episodes of depression they had experienced and what types of life stress they had encountered recently.
The results showed that people who had lost a parent or had been separated from a parent for at least one year before the age of 18 and individuals who had experienced more episodes of depression over their lifetime became depressed following significantly lower levels of recent life stress.
Additional analysis revealed that these effects were unique to stressors involving interpersonal loss.
"Researchers at UCLA and elsewhere have previously demonstrated that early adversity and depression history are associated with heightened sensitivity to stress," Slavich said.
"The present study replicates this effect but suggests for the first time that these associations may be unique to stressors involving interpersonal loss. In other words, individuals who are exposed to early parental loss or separation and persons with greater lifetime histories of depression may be selectively sensitised to stressors involving interpersonal loss."
An important question raised by these findings is how adversity early in life and prior experiences with depression promote increased sensitivity to stress. One possibility, the researchers say, is that people who experience early adversity or depression develop negative beliefs about themselves or the world — beliefs that are activated in the face of subsequent life stress.
Another possibility, which is not mutually exclusive, is that early adversity and depression influence biological systems that are involved in depression, perhaps by lowering the threshold at which depression-relevant processes like inflammation are triggered.
"Although many factors impact stress sensitivity," Slavich said, "thoughts almost always play a role. For example, when your best friend doesn't call back, do you think she is angry at you or do you think it just slipped her mind? Our thoughts affect how we react emotionally and biologically to situations, and these reactions in turn greatly influence our health.
"Regardless of your prior experiences, then, it is always important to take a step back and make sure you are interpreting situations in an unbiased way, based on the information available." - (EurekAlert!, June 2011)
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