Thinking about the problems which the natives of the Americas suffered when they met the Europeans, I wondered how a man of the past could survive in the modern age. Problems could be caused by pollution, different viruses/bacteria, different food (I wouldn't consider social/mental problems, only physical ones).
Of course we can't know it for sure, due to obvious lack of specimens, what I'm asking if there has been any well-thought theory about that, educated guesses, anything based of facts we know and what we can safely assume.
The "past" is left vague on purpose: as long as it's at least 100-200 years old it would be fine — though I can safely guess people from before the Industrial age would suffer much more than those who came after.