The connection between emotional stress and psychological illness remains fraught with uncertainty.
It is no secret that certain psychological illnesses, like depression for example, have physical symptoms.
According to the NHS, sufferers of clinical depression may exhibit changes in appetite and weight, unexplained aches and pains, disturbed sleep or, if you are a woman, changes to your menstrual cycle.
Multiple studies have investigated the extent to which your nervous system, which influences emotions, can predispose you to physical illnesses.
Dr Esther Sternberg, whose seminal work The Balance Within seeks to reconcile the central nervous system and the immune system, identifies a link – though not a causal one – between emotional state and inflammatory diseases:
The same parts of the brain that control the stress response … plays an important role in susceptibility and resistance to inflammatory diseases such as arthritis. And since it is these parts of the brain that also play a role in depression, we can begin to understand why it is that many patients with inflammatory diseases may also experience depression at different times in their lives.
Sternberg argues that, while feelings do not cause or cure disease, the biological makeup of both are similar enough as to affect the other.
Many of the nerve pathways and molecules underlying both psychological responses and inflammatory disease are the same, making predisposition to one set of illnesses likely to go along with predisposition to the other.
In another study by the American Psychological Association, 217 people were questioned about their work, and how stressed they were. Their saliva samples were also taken. Results found that those who exhibited low self-esteem or self-blame tended to have less immunoglobin-A, making them more susceptible to respiratory infections.
In a separate study, published in the Proceedings of the National Academy of Sciences, 270 participants were told to think of an event that made them feel either happy, or sad. Then, they were given a flu vaccine and monitored for six months.
Participants who exhibited better immunity – and more antibodies in their blood – were those with the strongest activity in their pre-frontal cortex, associated with positive thoughts.