Anecdotal: I have Chrohns and take 2000 UI Vitamin D everyday. I've been prescribed the lowest dosage anti-inflammatory (Mesalamine) for years and rarely had a flare up. My Vitamin D blood tests always come back in the normal level.
However, I can't get a good colonoscopy - my GI doc says the prep is always bad, even if I extend it for an additional day. He attributes that to a chronic simmering inflammatory state preventing things from cleaning out well. That puts me at a much higher risk of colon cancer, and so I'm also doing Entyvio infusions prophylactically.