From my experience, the religion seems to attract people with mental issues mainly because of a promise of paradise with no problems where life is perfect. For those raised in the religion I do think they become out of touch with reality and once you have awakened, frankly, everyone seems a little weird. For some that have aged in the religion, it leads to depression due to failed promises. Most of the female witness I know over 30 are on some type of medication for depression and some even share their medication with others blaming it on Satan and this system trying to wear Jehovah's people down.
I don't know if its higher in the JW organization, but its definitely noticeable.
The current wave of illness to recycle through the witnesses is fibromyalgia. Not mental but I'm sure it gives them something to talk about between RVs.