many yrs ago i started taking large doses of vit D.............i think i did hear it was good for ibs-d, but it does so many other things, too........not too long ago, my dr decided to check a bunch of levels & he said my vit D levels were really good & whatever i was doing, keep doing it...........i never told him that i was taking about 5,000I.U. a day, cause in the past when the drs i've been seeing hear what i do take, i get a lot of grief from them, so i just pay attention to how i feel & my skin, those tell me what i need to know.........i've been taking this amount for at least 5yrs...........now, i don't know if u know this, but u have to have enough vit A, calcium, magnesium, zinc, manganese & copper, to b able to use the vit D u r taking............& it's an individual thing..........as we age, it's also harder for us to make the cholesterol into vitamin D, as our skin loses some of it abilities to convert it...........i know that we r told how bad cholesterol is for us, but it does so many things & gets converted too..........it's considered a bad thing..........without enough of it, we don't make our hormones well or at least they get reduced..........one of those hormones is serotonin..........& about 70% of our serotonin is made in the intestines........this helps to relax our intestines, which will help with D..........there r so many things that help other things, not just what it is best known for...........