Last year an international panel of professional societies changed the definition of gestational diabetes. The blood glucose threshold for diagnosis was substantially lowered, more than doubling the number of women with the diagnosis. It will now encompass almost one in five pregnancies.

In his feature investigation this week (doi:10.1136/bmj.d2548), Ray Moynihan highlights this as just the latest example of how the definitions of common conditions are being broadened, so much so that by some estimates, almost the entire adult population is now classified as having at least one chronic disease.

Mental illness is an area of particular concern, he says, where controversy already bubbles around the definitions of attention deficit disorder, autism, and bipolar disorder. …