A great many things are labelled diseases nowadays. "Caffeine withdrawal" is a formal diagnosis, for example. But there are also examples of existing diagnoses getting expanded, such that more people are classified as unwell. Pre-diabetes and "mild cognitive impairment" (basically pre-dementia) would be examples.
This all creates higher risk of overdiagnosis and overtreatment. And it's worrisome that many of the doctors adjusting these definitions of disease have ties to drug companies.
Overdiagnosis is receiving a diagnosis that describes something that never would have hurt you, or caused you any discomfort. Overdiagnosis leads to treatment that, at least in retrospect, you didn't need. It's hard to tell if an individual has been overdiagnosed, but you can see it in statistics. One cause of overdiagnosis is this expanding of the definitions of disease.
How much is this happening? A study looked at guideline updates created by specialty societies and found that most of them expanded disease definitions. Few of them addressed the risk of overdiagnosis, and most members of the expert panels disclosed financial relationships with drug companies.
From one perspective, and a rational perspective at that, we have developed a self-perpetuating "medical-industrial complex" that seeks to do more and more good, at greater and greater expense, by identifying more diseases and treating them earlier. The blind spot of this system is not looking at trade-offs. One big trade-off is overdiagnosis.
Let's look at it from another perspective. During my primary care days, I would routinely see 80-year-olds with 15 chronic conditions. Apart from the fact it's hard to treat 15 diseases in 20 minutes, many of these diseases bordered on insignificant, in the greater picture. These weren't things that were going to kill the patient or cause significant discomfort. They represented risks.
For example, "chronic kidney disease stage 3" is important mostly because sometimes, in a small proportion of people, it progresses to stage 4 and stage 5 disease, and to dialysis. But I had several conversations with patients who, after looking at their records, needed to know what was wrong with their kidneys. Is the anxiety worth tracking that problem and putting a label on it? That's part of the trade-off.
Expanding technology has changed disease definitions. Years ago, you would have a heart attack, and that was that. Then we developed the EKG, and the definition became electrical. Now we have sensitive bio-markers in the blood, and they eclipse the previous definitions.
But then you use the test on healthier people, finding subtle abnormalities. So when you look at someone with severe pneumonia, those heart biomarkers (e.g. troponin) go up a bit. Has this person had a heart attack now? Some would say, "Yes, they had a non-Q wave MI."
That's how one branch of overdiagnosis works: using technology to see what it can do, without considering the trade-offs.