These factors are important to health in and of themselves for anybody, of course. However, I believe there is an additional reason why they assume added importance for a Hygienic lifestyle in particular. Stress and vegetarian diets. Again, I am not saying this is true of all, but it is a noticeable thread. And a number of Hygienic practitioners are noted for continually reminding the rest of us not to shirk these factors.
Stress creates less margin for error for nutrition's contribution to physiological maintenance.
This leaves less margin for error with regard to nutritional intake. And that would presumably also have the potential to affect any cellular rebuilding and repair necessitated by stresses. This expands the margin again to create a bigger cushion. Of course that's not the only thing to expand one's safety margin. The second thing is that there is more diversity in the way Hygienists in the real world actually approach the dietary aspect of the system than is publicly acknowledged in the pages of ANHS's Health Science magazine, for instance.