Take at a Different Time of Day
Two case reports suggest that calcium carbonate interferes with the body's absorption of thyroid hormone when both were taken at the same time.
A prospective cohort study has validated these case reports.
Twenty individuals with hypothyroidism stabilized on long-term levothyroxine therapy were included in the trial. Participants were given calcium carbonate (1,200 mg daily of elemental calcium) for 3 months. During the period the calcium supplement was taken, thyroid hormone blood levels declined. But after calcium supplementation was stopped, thyroid levels climbed back up, slightly surpassing the levels measured at the beginning of the study.
It is thought that calcium combines with thyroid hormone, thus reducing its absorption.
To prevent this interaction, take thyroid hormone and calcium supplements as far apart as possible.