I am 17 years old, was diagnosed with type one diabetes nine years ago, and at that time. it was also noted that I had an enlarged thyroid gland so I began to take Synthroid. I was told that I would most likely be able to stop taking this medication at age 17 or 18, but at my last endocrinologist visit, I was told that I will most likely need to continue taking this medication until I finish college. I have read that, in people with type 1 diabetes, the immune system often attacks the thyroid gland and do not understand how, if my thyroid glad has indeed been destroyed by my immune system I will be able to stop taking Synthroid. Can you tell me which thyroid hormone “Synthroid” is? Is there any reason that this hormone would be needed after growth has been completed? Is there any reason not to stop taking it? I intend to also ask my endocrinologist about this but would like to have some information already so that I may ask good questions.

This combination of type 1 and hypothyroidism is almost certainly part of a condition that is now called the Autoimmune Polyglandular Syndrome Type II. It would be worth discussing this with your endocrinologist because, although diabetes and hypothyroidism are by far the most common autoimmune components, there are others less common like the celiac syndrome that nowadays are often routinely looked for just to be forewarned.

As to the time that you might discontinue using Synthroid, this really depends on how much residual thyroid hormone is preserved after growth is completed; some hormone is certainly needed for normal metabolism throughout your life. The TSH test is a simple way to determine your thyroid status. Synthroid is the synthetic version of the normal thyroid hormone T4.

DOB
Additional comments from Dr. Stuart Brink:

Nobody would ever be able to tell you that you would not need thyroid hormone after growth is completed. However, if you only had mild hypothyroidism caused by Hashimoto’s thyroiditis, there is some possibility this could be the case. Anyone with Hashimoto’s thyroiditis who is hypothyroid or even just with a goiter would likely need thyroid hormone replacement sometime in their life. The more abnormal the antibody titers, and/or the more abnormal the main thyroid function results, the greater would be the likelihood. It has nothing at all to do with your having diabetes only that both are autoimmune endocrine disorders. We and others have found about 20-40% of people with type 1 diabetes will have Hashimoto’s thyroiditis and about one quarter to one half of that subgroup would eventually need thyroid hormones. Synthroid is pure, synthetic thyroid hormone, T4 or levothyroxine. There are several similar preparations on the US market and others around the world. They are not always equivalent so we and many others do not believe that changing one to another brand is wise. There is some controversy about this, however.

The real answer to your questions, whether you still need Synthroid replacement could be determined by your endocrinologist based upon the thyroid blood work over the years, what pattern exits, if any. And, then what happens as you slowly taper down your dose and how your body responds.

SB
Additional comments from Dr. David Schwartz:

There are two primary thyroid hormones: one is called “thyroxine” and is abbreviated T4 (because it has 4 attached iodine molecules); the other is called triiodothyronine and is abbreviated T3 (because it has 3 iodine molecules attached). T4 is more abundant in the body; T3 is more potent.”Synthroid” is T4. The body will convert T4 into T3.

I fear that either you were given false information or there has been misunderstanding. It is actually rather uncommon for someone to be able to come off of T4 therapy when there is autoimmune inflammation of the thyroid gland. The thyroid hormones are required for normal day-to-day metabolism and are required in adults as well as during childhood growth.

DS
Additional comments from Dr. Tessa Lebinger:

Synthroid is a synthetic version of levothyroxine (T4). The thyroid gland makes mainly T4, much of which is converted to tri-iodothyronine(T3) in different organs of the body. The thyroid gland makes a small amount of T3. Until recently, we used to think it was best to give everyone only T4 and let the body convert what it needs to T3. Now there is some evidence that we should be giving back a little bit of T3 also, but this is somewhat controversial.

In any case, most likely you will need the thyroid hormone even after you stop growing. Every organ in the body needs thyroid hormone to stay healthy, and often pregnancy can retrigger a thyroid problem. An untreated underactive thyroid during pregnancy increases the risk of miscarriage and possibility normal brain development in the developing baby. As long as you don’t take more than your body would make, your body should be able to just make less and not have any problems (unless your body starts making too much thyroid hormone on its own, in which case it can’t make less). In most cases, it is just best to continue the thyroid hormone indefinitely unless there is a problem and be careful not to give too much.

TGL