Is stress a potentially contributing factor to the development of psychosis?

Professor Robin Murray: We have done a lot of research in the last ten years that does indeed indicate that social factors are important. These may be things that happen near to the illness, so for example, having some adverse event, particularly threatening or victimisation events, may make people more prone to paranoia.

For example, if you get an event where you lose somebody, like a spouse or a brother or sister, it’s more likely to predispose you to depression, but if you get an event where you’re attacked in the street or some threat involved, this is more likely to, if you have a susceptibility, to bring on paranoia or psychosis. We know that these adverse events, the stress, probably increases your cortisol levels, and this in turn can precipitate the psychosis.

We know that when any normal individual is stressed, this has an effect on the pituitary gland in the brain, and this in turn causes the production of cortisol, which is really the ‘fight or flight’ response, and so this is an entirely healthy thing when the stress just occurs for half an hour, or for a day.

But if you have continually high cortisol levels, then this can begin to impair the health of the nerve cells in a particular bit of the brain called the hippocampus. And we know also that the hippocampus can be damaged by birth complications, and we know that the hippocampus is involved in the control of the levels of dopamine.

So if you start off, for example, with a slightly more vulnerable hippocampus because of something that’s happened in your brain development, and then you’re stressed, this puts up the cortisol level, and if that persists over a long period of time, it can cause what’s called a ‘second hit’ to the hippocampus, and this in turn can cause some dis-control of the dopamine. So we regard the cortisol as a precipitant, which in somebody who is vulnerable, can bring on the illness. Now in the rest of us, who have not had any of these developmental problems, we would just be stressed and we might get anxious or depressed, but we wouldn’t go on to develop hallucinations or delusions.

There is a lot of evidence that migration increases the risk of psychosis. Migrants everywhere have an increased risk of psychosis, to a greater or a lesser extent.

Why should migrants be at increased risk? Well, you just have to think of yourself in a foreign country. Would you buy a second-hand car in Greece? It’s difficult enough buying a second-hand car – you wonder if the garage man is fiddling you, but if you are in a foreign country, Greece or Finland or Spain, then you don’t know how to read his facial expressions, you don’t know really what the right price is, you are more prone to paranoia.

Another example is you go on your holiday, you get off at the airport, you take a taxi, how long is it before you begin to think the taxi driver is driving round in circles in order to increase the amount he can charge you, so you’re a bit more wary when you’re in a foreign country or somewhere you don’t quite understand the social norms.

So this probably provokes increased liability to paranoid psychosis in migrants. What we do know, that this seems to be a problem particularly for black migrants into the UK.

So, for example, if you are born in Jamaica you are no more at risk of developing schizophrenia if you stay in Jamaica than any white person, But if you then migrate from Jamaica to the UK, your risk goes up significantly. And we think this is probably related to the stress of migration and being a migrant in an unfamiliar situation.

So we know that migrant populations tend to have a poorer education, they tend to have poorer housing, particularly black populations, may have more difficulty getting a job, they may be subject to discrimination, or they may have difficulties with the police, now maybe, you can actually, by causing repeated discriminatory events to happen to someone, you may actually begin to make them think that the society is against them, well it may be in part, but even when it’s not, this may provoke a paranoid way of thinking.