I crave more salt than sugar, but I definitely think sugar has some role to play in this, or at least influences POIS symptoms.
In the last two weeks I've given up all sugar completely - including, controversially, fruit - and I feel a lot better for it. When I took niacin before, coupled with a normal diet, ie one with sugar in it, I still got quite heavy symptoms; but cutting out the sugar completely has made a big difference. It's a big sacrifice, of course.