I find the concept of hormesis in general quite fascinating. We had a brief mention of it in one of my classes, and it refers to the possible phenomenon that exposure to low stress or harm can actually produce some benefit. My professor told us (according to my notes) that in Hiroshima's close vicinities, there was a high incidence of tumors and general all-cause mortality rates (if you weren't killed right away), but a little further out, the life expectancy of the population was actually higher than that of populations even further away from the site. One proposed mechanism is that the body's protective measures are being stimulated by short-term exposure. Now, my prof emphasized it's the ACUTE radiation exposure that has been linked, although the Wikipedia article on radiation hormesis specifies that it's the chronic exposure.
Exercise, as a kind of physiological stress, can be considered another example of hormesis. I don't know whether it deserves to be classified as acute or chronic, however. Daily exercise is what confers major benefits, not isolated strenuous workouts once every couple months, but it's not the same kind of stress as career-related ongoing stress from a job over decades, which is usually considered bad. I would lean towards classifying exercise as regularly scheduled acute stress.
Low daily intake of alcohol has been considered possibly beneficial for cardiovascular health, although we all know that alcohol in general is a toxic substance to the body and binge drinking is terrible for you!
Broccoli and related greens like brussels sprouts, kale, etc. contain a substance (is it sulforaphane, or indole-3-carbinol, I don't remember, or maybe it's both) that is actually a kind of plant toxin, but it's been posited as an anti-cancer/anti-tumorigenic substance because of perhaps how the body reacts.
Lots of other substances, like cigarette smoke or coffee, induce increased levels of liver enzymes which promote more efficient detoxification. I'm definitely not telling anyone to start smoking (or to intentionally expose themselves to higher levels of radiation), but it's kinda cool that it happens. In one observational study, regular coffee drinkers were associated with having lower rates of liver cancer.
Really neat stuff.