Many times over the years, I have heard in various contexts, in many different variations, basically the phrase/sentiment:
My secret to staying healthy is simply to never smoke, drink or use loose women!
The "loose women" part could also be "bad women" or a whole sleeve of other words. I assume that by "use", they refer to prostitutes, and perhaps specifically "low-class" such (as opposed to "gold diggers").
My guess is that this phrase origins from "back in the day" and that it was assumed that prostitutes ("fallen women") had all kinds of diseases, combined with nonexistent or rare use of protection?
So they basically mean that smoking and drinking are (quite obviously) bad for your health, but so is having sexual intercourse with disease-carrying females, as you run a high risk of also getting whatever illness they have, thus directly affecting your health?
However, it could also mean that the "loose women" cause problems with one's marriage, thus stress, thus also affects your health that way. In fact, it seems reasonable that this could be what is primarily/solely referred to with this phrase. Or maybe that simply having sexual intercourse with anyone will drain you from your energy? (Although I'd think it was the exact opposite...)
The bottom line is that it doesn't seem obvious why exactly these "loose women" are so "obviously" bad for one's health, and it bothers me that I still can't tell exactly what they are referring to.