Anytime you overclock ANYTHING, you are decreasing the probable lifespan of it's components. There are no exceptions to that rule. The only question is whether the decrease is significant enough to be a concern, and that has to be judged on a case by case basis. Some minor to moderate overclocking of most CPUs or graphics cards is unlikely to cause any significant degradation to happen prematurely, but anything beyond that is purely "it might, it might not".
If you can reach an overclock on core or memory clock, that is stable, and remains within and preferably a comfortable distance below, the thermal specifications for that component, then it's probably fine. That does not change the fact that ALL overclocking that involves increasing voltage will shorten the lifespan of anything you do that to. Some cases you can actually increase the clocks on something, CPU or GPU, and REDUCE voltage, and remain stable, but doing extensive stability testing should be a priority and should never be skipped or shortcutted. Ever. If you are going to overclock, then do the work required to verify you are thermally compliant and that the configuration is as stable as can be verified for.