When an upper limit is given for the supplemental form of a nutrient, do naturally occurring forms count towards the total? e.g. The UL for supplemental Niacin is 35mg. If I intake 20mg from food and 25mg from a daily vitamin, is that considered over the limit?
Depends on the nutrient. Some only have adverse effects when taken as a supplement.
I like the Oregon State University’s Linus Pauling Institute for mcronutrient research website for learning about details like that, but the menu tab for this sub has resources recommendations also.
The RDI limit is usually given to supplement makers as the ‘upper limit’ they can include of a certain nutrient.
But this required/recommended daily intake limit usually infers as the MINIMUM amount of that certain nutrient required to stay healthy in the broadest spectrum of people.
This means you need AT LEAST what the RDI is. Not what your body can take advantage of.