Yes and no. It depends on the over clock. If you get to a higher frequency like say 4.6 or 4.8 then yes life span is going to be affected, but it also depends on if you're running the over clock at a 24/7 thing, as in you forced the clocks to run at 4.6 or 4.8 at all times, rather than when under load. You can make it to where it will only run that way when under load. Also, depends on if you're running adaptive mode or not. Without adaptive mode, an application can make it use more volts than it is actually at. So say you put the voltages at 1.2 at a 4.6 over clock, and and application makes it draw more than 1.2.. Well, that could be bad, really bad. But, that is where adaptive mode comes in(This is all in your bios).
But to sum it all up, it depends on your chip, your quality of cooling, and really... You're pushing it to run out of spec, so you're getting more performance than what you would normally get, thus you're going to affect the life in most cases. However, if you buy the intel plan if you fuck your CPU, you can get a free replacement(Haswell only, as far as I am aware).