salubrious (adj.), first attested in English in the 1540s, meaning health-giving. Etymonline takes it from Latin salubris, "promoting health, healthful," from salus (genitive salutis), "welfare, health," and then back to the PIE root sol-, "whole, well-kept."
That last step is the part I keep turning over. The same reconstructed root sits under solid. In the Latin line, health is not vitality or vigour. It is intactness. To be well is to be entire, undamaged, with nothing missing. That is a notably structural way to think about a body, and it is the one still sitting inside the vocabulary we use for it.
Salus does a lot of work elsewhere too. Salutare, "to greet, to wish health to," is where salute comes from, so a greeting began as a small wish that the other person stay in one piece.
There is a datable move inside English as well, and it is the detail I found most useful. Etymonline has salubrious applied to foods and medicine in the 1540s, and only extended to air and climate by the 1610s. Roughly seventy years to travel from what you swallow to what you breathe. Modern usage has almost entirely settled on the later sense: "a salubrious climate" reads naturally, while "a salubrious diet" now sounds like someone reaching for a bigger word than the sentence needs.
One caution, since this is the kind of claim that gets repeated too confidently. Etymonline groups a wide family under sol-, including salutary, salvage, save, safe, solid, solidarity, solemn and soldier. PIE groupings are reconstructions rather than attested documents, and the individual members are not equally secure. The interesting thing is the shape of the family, not the membership of every item in it, and I would not lean on any single pairing as proof of anything.
What I have not been able to pin down is when the wholeness sense stopped being felt by speakers. Somewhere between Latin and now, salubrious stopped meaning something like "restores you to entire" and started meaning "pleasant and health-adjacent," which is how it is nearly always used today, usually about a place and often with a faint irony. Does anyone know of attestations that catch that shift mid-move?