Women taking thyroid hormone medications should not take them with their calcium supplements. Studies suggest that calcium interferes with the absorption of thyroid hormones in the body, making the hormone treatment ineffective. Simply taking the two medications at different times of the day solves this problem.
It is thought that calcium may bind to thyroid hormone, reducing its absorption in the body. Studies have shown that thyroid hormone blood levels drop when patients take calcium supplements along with their thyroid medication. If they stop taking calcium or take it at a different time of the day than when they take thyroid pills, the thyroid hormone level climb back up.
The authors of the original 2000 report in JAMA remind patients about these types of drug interactions in a WebMD Heath News article, “It is critical for thyroid patients to tell their physicians about all the medications they take”. Other studies have shown that widely used medications like antacids, iron supplements and ulcer treatments can also interfere with thyroid hormone activity.
Boyles, S., 2000. “Calcium Supplements May Interfere With Thyroid Treatment,” WebMD Health News. http://www.webmd.com/news/20000606/calcium-supplements-interfere-thyroid
Singh, N. et al, 2000. “Effect of Calcium Carbonate on The Absorption of Levothyroxine,” JAMA http://jama.ama-assn.org/cgi/reprint/283/21/2822?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=1&andorexacttitle=and&andorexacttitleabs=and&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&sortspec=relevance&volume=283&firstpage=2822&resourcetype=HWCIT
Greenspan, F., no date. AllThyroid website information about the risk and treatment of osteoporosis: “Osteoporosis,” Thyroid Foundation of America.
Nippoldt, T., no date. Q&A from Mayo Clinic website regarding calcium’s interference of thyroid treatments: “Hyperthyroidism: Can Calcium Supplements Interfere with Treatment?” http://www.mayoclinic.com/health/hypothyroidism/AN01181
Shomon, M., 2003.