Yes, many things will impair the absorption of T3. I forget the complete list of known culprits, but iron is a major one in addition to calcium, aluminum, magnesium, and some other Rx meds. When patients come into clinic with increased thyroid requirements, 90% of the time it is because they started taking multivitamins and absorption is impaired. They obviously haven't studied every component of a multivit to determine which of them are responsible because that would be unreasonable, so the American Association of Clinical Endocrinologists recommend taking thyroid meds alone on an empty stomach since food will impair absorption as well.