What causes depression? It's a simple question – but the truth is that we don't really know the answer. Treatment tends to be of the hit-and-hope variety. You may get medication to chemically tweak your serotonin, but in some cases this can make things worse rather than better. You may be offered psychotherapy – but what if talking is not what you need?

According to a leading professor of psychiatry, there could be a simple, physical cause that plays a major role in mental health issues and can transform the way we treat depression: inflammation.

Edward Bullmore from the University of Cambridge told my podcast that if we abandoned the one-size-fits-all approach to depression and did blood tests on patients, we would have a better idea of the cause and the ability to target treatments. Because the fact is that at the moment we are not getting much of a grip on the illness. Global levels of depression continue to rise, to the point that depression is the biggest single cause of disability worldwide, according to the World Health Organisation.

“Depression is incredibly common,” Prof Bullmore said. “Is it plausible that something that affects so many has the same cause in each of us? I don’t think that’s particularly likely. There may be some people with depression where inflammation is an important cause, driving their symptoms, and that could open the door to a rather different treatment, rather than the current one-size-fits-all approach where you go to see your doctor and they prescribe SSRIs or psychotherapy.