I can say honestly that my wife is better on it than not, in the winter, as she suffers from SAD. I'm currently on 10,000 IU full time and I have her on 4000/8000 summer/winter. There's no mistaking the positive impact in my eyes after being with her for 12 years now and having tons of time in to recollect and go by.
Anyone that knows me knows I'm a huge fan/follower of Dr Rand and he is very vocal about 10k IU/day ful time, and especially if running gear. Thats good enough for me and given how cheap it is....
@BobTheOldLifter Out of curiosity what marker are you watching? Total?