Rather than define an objective measure of the problem, they (by definition) effectively define the percentage of the population affected.
In other words, osteopenia is defined in such a way that it is not curable, preventable, etc.
What is the point saying, “disease X affects 5% of the population by definition”.
It’s like throwing away half the resumes for a job position and saying we don’t hire unlucky people…
Between 1.0 and 2.5 standard deviation is something like 15% of the population. “1.0” and “2.5” are ridiculously round number. What is the medical significance of such?
Sure, at some point, it will be correlated with fragile bones.
Adult male height is roughly 5’9” with standard deviation of 2.8”.
We DON’T say adult males under 5’2” are diagnosed as having medical disease.
People are, on average, fucking shitty people.
If males under 5’2” were having clear difficulty functioning and outcomes were measurably worse for most of them and large numbers of them were seeking treatment and we actually had safe and effective treatments which measurably decreased or eliminated the problems caused by the fact that they are under 5’2” for most of them, then I'd expect that we would consider it a medical disease/disorder. Why shouldn't we?
As a heuristic for identifying when something deserves attention?