Like with salt, there is definitely such a thing as too little of it though.
How do you know that it's not like alcohol, where there all levels of consumption increase cancer risk?
There's a similar controversy about radiation hormesis[1]. Personally my suspicion is that low doses are at least harmless if not therapeutic, because of the evolutionary benefits of the stress response[2]. However I do freely admit that it's possible that there is no therapeutic or even safe level of alcohol consumption. Similarly there may be no safe level of BPA exposure or any number of other stressors.
Ah yes the classic some’s good more’s better fallacy. Some salt is good on food, but keep adding more and it’s inedible. Just because there isn’t a discrete point where you can say it’s too much (that one grain made it too salty) doesn’t mean that there’s no such thing as too much.
There are many other such cases, for example drug titration springs to mind.