1.3 Early life events and stress
One of the most potent factors associated with mental disorders such as depression and anxiety later in life is mistreatment and abuse in childhood (Browne and Finkelhor, 1986; Turner and Lloyd, 1995). This includes sexual abuse as well as physical, mental and emotional neglect or mistreatment.
Child sexual abuse affects at least twice as many females as males and appears to be a particularly powerful risk factor for adult-onset depression (Weiss et al., 1999). It is also a strong predictor of post-traumatic stress disorder (Browne and Finkelhor, 1986). It may therefore be a factor that contributes to the well-established epidemiological finding that women are much more likely to be diagnosed with depression and other emotional disorders than men, not only in England – see Figure 3 – but around the world (Weissman et al., 1996).
Childhood abuse may have psychosocial consequences that increase the risk of depression, as it can lead to shame, humiliation, isolation and an inability to trust others.
Another possibility is that, especially if severe and repeated, childhood abuse biologically sensitises the stress response systems of children so that stress is triggered much more easily later on, and for longer periods (Perry et al, 1995).
An important study by Christine Heim and her associates (Heim et al., 2000) showed that the stress response of women who had suffered childhood abuse (sexual or physical) did indeed show evidence of having been ‘sensitised’. The women in Heim’s study fell into four groups:
- ELS/MD: those who experienced early life stress (ELS) – that is, were sexually or physically abused as children, and were also diagnosed with major depression in adulthood
- ELS/no MD: those who were abused in childhood but did not get depression
- No ELS/MD: those who did not suffer child abuse but had major depression
- Controls: those with no history of childhood abuse or depression, who acted as a control group.
All the women underwent the Trier social stress test, which involves public speaking and solving arithmetical problems in front of a critical audience. The levels of the stress hormones ACTH (adrenocorticotropic hormone) and cortisol in the women’s blood were measured before, during and after the test, as were their heart rates (Figure 4). When individuals feel threatened the SNS (sympathetic nervous system) is activated and this leads to the release of adrenalin, which elevates heart rate. Stressors also trigger a parallel stress response involving the hypothalamus, which triggers release of ACTH (adrenocorticotrophic hormone) from the pituitary gland, which in turn triggers the release of cortisol from the adrenal cortex.
Figure 4 shows that before the Trier test, the four groups of women did not differ significantly on any of the three measures of stress, but some clear differences emerged during the test.
Was there a clear difference in any of the stress response measures between women who had and had not experienced childhood abuse?
Yes, Figure 4a shows that ACTH levels were markedly higher in women who had been abused as children (ELS/MD and ELS/no-MD) than in women who had not been abused (no-ELS/MD and the controls, no-ELS/no-MD).
Women whose stress systems were most reactive in the test were those who had been abused in childhood and were also currently depressed (ELS/MD). They showed the most extreme responses in all three measures – a rise in levels of ACTH and cortisol and an increased heart rate. Thus there is evidence for a marked sensitisation of the stress response system, and a link with depression, in at least some women who experience childhood abuse.
However, note that not all women who experience childhood abuse develop depression (ELS/no-MD group), and not all women who are depressed as adults have experienced childhood abuse (the no-ELS-MD group). This suggests that other risk factors must be operating for depression to develop. There are many possibilities. For those who were abused, the level and kind of abuse may matter. Social and psychological support networks available during childhood and adulthood, or genes that make some women more vulnerable to stress or affect other personality factors, could also play a part.
Having considered the role of stressful life experiences we next look at how cognitive factors can also play a part in emotional disorders.