My sister has been taking Vitamin D capsules for a few months and has noticed that her stools are darker, sometimes even black. She’s heard that black stools can be linked to iron supplements but isn’t sure if this applies to Vitamin D. This is concerning for her because black stools previously led to the removal of two colon polyps, and she isn’t due for another colonoscopy for two more years. Has anyone else experienced black stools while taking Vitamin D? She’s taking 2000 IUs a day.