I wonder if this title isn't a bit backwards. We are creatures that emerged from nature; being in nature is baseline to us. A better way to phrase this might be "being constantly trapped in a world made of concrete and drywall causes enormous emotional and cognitive detriments to people".
Natural systems are effectively infinite fractals, most urban structures are flat and relatively featureless by comparison. Living in a city is sensory deprivation combined with overwhelming discordant stimuli (engines and sirens mostly.) And that's before you get to the incredible chemical burden of living in a city. In fact, until very recently, cities were populations sinks. People died in cities faster than they were born.