Your thyroid produces hormones that control the rate your body uses energy -- known as your metabolism. If you have an underactive thyroid gland, called hypothyroidism, your doctor may prescribe a synthetic thyroid hormone replacement medication called levothyroxine. You'll need to take levothyroxine every day, most likely as a lifelong treatment. Certain foods, vitamins and chemical compounds can interfere with the absorption of levothyroxine, especially vitamin supplements high in iron and calcium.
Hypothyroidism and Levothyroxine
Levothyroxine is sold under a variety of brand names, including Synthroid, Levoxyl and Unithroid. Levothyroxine replaces T4 hormone, one of two important hormones -- T3 and T4 -- that control metabolism. Your body can synthesize T3 hormones from levothyroxine even if you are hypothyroid, so there is rarely a need to supplement both T3 and T4 hormones. In addition to a slower metabolism and weight gain, common symptoms of a sluggish thyroid include fatigue, headaches, a sensitivity to cold, depression and a goiter -- a physical swelling of the thyroid gland at the base of your throat.
Levothyroxine is designed to be absorbed in your intestines during digestion. Any drugs that interfere with digestion can block the absorption of your hormone replacement. The Mayo Clinic notes that iron supplements and vitamins that contain iron, calcium supplements, antacids containing magnesium and aluminum and certain cholesterol and ulcer medications can stop your body from assimilating levothyroxine. You do not have to stop taking your supplements or other medications, but you must wait four hours after taking levothyroxine to avoid any potential interactions.
Vitamins and Levothyroxine
While there are no vitamin supplements designed to be taken with levothyroxine, the University of Maryland Medical Center notes that some vitamins may help relieve the symptoms of your hypothyroidism. UMMC recommends eating whole foods, rather than taking supplements to increase your consumption of foods high in B vitamins, such as whole grains and fresh vegetables and fruits and vegetables high in antioxidants, such as blueberries, cherries, bell pepper, squash and tomatoes. Omega-3 supplements may decrease inflammation and strengthen your immune system. You can also increase omega-3 intake by eating fatty cold-water fish, walnuts and flaxseeds.
Any vitamin supplement that you and your doctor agree should be added to your diet can be taken with levothyroxine, provided that you don't take your vitamin or supplement within four hours of taking your thyroid replacement hormone. Fiber supplements and high fiber foods should also be taken well after the levothyroxine has been absorbed by your body. Certain foods, including walnuts, cottonseed meal and soybean flour may also interfere with levothyroxine and should be eaten later.