Depression is an extremely debilitating psychological disorder. It is characterized by periods of low mood, but is also associated with a number of other symptoms, such as disturbed sleep and appetite, low self-esteem, and an inability of the brain to function properly. Moreover, depression is the 4th leading cause of disability worldwide; each year 6% of adults will experience an episode of depression, and over the course of a lifetime 15-20% of the population will experience at least one depressive episode.
To put it into context, each year 3.69 million people in the UK will suffer from depression. That’s a huge number. In fact, that’s much larger than the population of Wales. Yet surprisingly we, as scientists, know very little about the disease. For example, we don’t really know what causes depression; we don’t know why some people develop depression while others don’t; and we don’t have brilliant treatments, as a proportion of the population are
unresponsive to antidepressant medication and psychological therapies.
So what do we know about the disease? Well one thing that we are sure of is that there are certain risk factors associated with getting depression. For example, psychosocial factors such as unemployment or poverty increase the risk depression, as do stressful life events, such as the death of a loved one or being fired from a job. Recently it has become increasingly clear that stressful life events during early life, such as childhood maltreatment or abuse, also increases the risk of that person developing depression later on in life.
So this got us thinking – what if even earlier insults from the environment, such as those a fetus might experience in the womb, could increase risk for depression?
We got this idea from a big body of research, which supports the ‘fetal programming hypothesis’. This theory was developed by the late David Barker, to explain why those babies born with a low birth weights were more likely to develop diabetes and heart disease in adulthood. The theory suggests that if the womb environment is not perfect to support fetal growth, then the fetus adapts in such a way that makes it more likely to survive. For example, if a mother is malnourished while pregnant, energy available for fetal growth is directed away from the heart and to the brain, to ensure adequate brain development, and also the fetal metabolism is changed to support survival in a low-energy environment. However, in this case short-term gain equates to long-term pain, because in adulthood this person will be more likely to suffer from heart disease and diabetes.
We wondered if the same might apply to depression in adulthood, and thought that perhaps something could be disrupted during fetal development, which may increase risk for later depression. We carried out a review of the literature, focusing on studies that had investigated certain fetal exposures, such as maternal smoking, taking drugs, malnourishment and distress, and which also measured depression as an outcome later in life. As this is a relatively new idea, very few studies met our criteria, and we only managed to find 16 papers.
Interestingly, we found that those people who had been exposed to maternal psychological distress, alcohol and under nutrition in the womb were more likely to develop depression later in life than those people who were not.
Of course this is a very interesting finding, but it is important to remember that there are still relatively few studies and those that exist have some limitations.
Nonetheless, our review article highlights that environmental insults during fetal development potentially increase risk for depression in later life, addressing the intriguing possibility that susceptibility to depression may begin before birth.
If you would like to read more about these findings, and our discussion of the potential mechanisms that may mediate
these associations, our review is available to download here.