How do you know that in our environment today we get enough?

My expectation is that in times of such plenty as the present, anyone not in poverty or following some very restricted diet will find it difficult not to get enough of everything.

In my case, I'm well-off and eat whatever I want, which is much the same range of things in much the same quantities, year after year. Therefore if I have a deficiency, it must be a chronic one. But I have no chronic health problems beyond slowly decaying teeth and the aftereffects of an acute illness many years ago of unknown aetiology. Therefore, I conclude, I experience no chronic dietary deficiency. (I have not seen dietary supplements touted as a cure for tooth decay, and I have seen everything touted as preventatives for diseases with no known cause.) I am over 50, so I think that's long enough a trial.

(Digression: fun fact for bright young things! Nearly everyone over 50 has at least something that has gone wrong with their bodies and will never be fixed. I suspect that not many young people in good health realise this. Barring radical advances in medical science, this is what you have to look forward to.)

There are those who say that health is more than just the absence of illness, but I've never been able to make out what they mean. Perhaps by "health" they mean being possessed of great physical energy and joie de vivre, rather than merely being free of identifiable problems, but I've never seen anyone attribute that to supplements except the people selling them. I haven't particularly looked, though.

Those of you who do take dietary supplements: in what ways do you feel different, depending on whether you take them or not?

I read Seth Roberts' blog, and this sounds like something he might have addressed, but Googling ["Seth Roberts" vitamins] didn't turn up anything.