Important news for the millions of people with hypothyroidism was released at ENDO 2017, the Endocrine Society's 99th annual meeting in Orlando, Florida.
Deborah Chon, M.D., reported on results of a preliminary study that showed that cow's milk can significantly reduce absorption of the most commonly prescribed thyroid hormone replacement drug, levothyroxine, when taken at the same time. (Levothyroxine is the generic for brand names that include Synthroid, Levoxyl, and Tirosint.) Levothyroxine is one of the most frequently prescribed medications in the United States.
Calcium supplements and calcium-fortified juice have been scientifically demonstrated to affect the absorption of levothyroxine, a drug used to treat hypothyroidism, an underactive thyroid. Given this known interaction, practitioners typically recommend taking levothyroxine and calcium at least three to four hours apart. Milk, however, had not been studied in depth until this research. According to the research abstract, cow’s milk contains approximately 450 mg of calcium per 12 oz. serving.
According to Dr. Chon, who is associated with the UCLA David Geffen School of Medicine and the Veterans Affairs Healthcare System in Los Angeles, California, "Decreased absorption means that patients may not get the full dose of thyroid hormone that they are prescribed."
In the study, Dr. Chon and her research team evaluated a group of subjects and measured their total T4 levels after taking levothyroxine alone, compared to two percent milk. Their total T4 was measured one, two, four, and six hours after taking the levothyroxine. They found that those who consumed milk at the same time as the levothyroxine showed significantly lower absorption of the drug, and lower total T4 levels.
"The main message of this study is that patients managed with thyroid hormone replacement therapy should be advised to avoid taking levothyroxine simultaneously with cow's milk, given its interference," Dr. Chon said.
How to take your thyroid medication
These new findings add to the guidance on how to take your levothyroxine for optimal absorption. These recommendations include:
- Take your levothyroxine first thing in the morning, and wait an hour before eating. Taking food at the same time can slow or impair absorption of levothyroxine.
- Wait an hour after taking your levothyroxine before drinking coffee, including decaffeinated coffee. Coffee has the ability to impair absorption of levothyroxine.
- Wait at least three to four hours before taking calcium supplements, calcium-fortified orange juice, or iron supplements, given their ability to impair absorption of levothyroxine.
- Consider taking levothyroxine at bedtime. Research has shown that levothyroxine absorption may be improved by taking the medication in the evening. Nighttime dosing also allows you to eat, drink milk and coffee, and take calcium or iron supplements in the morning after waking.
Benvenga S., Bartolone L, Pappalardo MA, et. al. Altered intestinal absorption of L-Thyroxine caused by coffee. Thyroid. 2008.18(3):293-301.
Mazokopakis E. Interaction between levothyroxine and calcium carbonate. Canadian Family Physician. 2008;54(1):39.