What is the thyroid and what does it do?
The thyroid is a butterfly-shaped organ in the front of the neck. It makes and releases stuff called thyroid hormone. (Actually, the thyroid makes two closely-related hormones, called T3 and T4 -- or if you prefer long-winded medical jargon, triiodothyronine and thyroxine. T4 is converted to T3 after release from the gland, but the conversion is rarely a problem.) The production of thyroid hormone is dependent on the health of the thyroid gland, and on the stimulation of production by another hormone, TSH (AKA thyroid stimulating hormone).
Sometimes the thyroid gland is enlarged, in which case it may be called a goiter. Enlargement of the the size of the gland may occur from lots of reasons, but that's not usually the big issue of what can go wrong in folks who have diabetes: their main problem usually is either making too much or too little thyroid hormone. When the gland produces too much thyroid hormone, it causes a medical disorder called hyperthyroidism; when it produces too little, it's called hypothyroidism. Having either too much or too little thyroid hormone can really mess up one's diabetes control, as well as provoking annoying symptoms, and increasing the risk of medical complications.
Typical symptoms of an overactive thyroid gland include
- hand tremor
- rapid and irregular heartbeat
- weight loss
- nervousness, jitteriness, or irritability
- increased sweating
- heat intolerance: I recall one patient who could sleep with the windows open in winter in Alaska (which is when he realized he had a problem)
Hyperthyroidism is more likely to occur in people with type 1 diabetes, as they both frequently have an autoimmune cause. Women are more likely to develop hyperthyroidism than are men, and it runs in families. Testing for hyperthyroidism is usually straight-forward: measurements of T4 and T3 show elevated values, and the TSH level is usually well
below normal. Treatment depends on the cause the severity of the hyperthyroidism, and includes three options: medications, treatment with radioactive iodine, and surgery. In my opinion (and that of most endocrinologists, I suspect), folks with both diabetes and hyperthyroidism should be referred to an endocrinologist to evaluate which therapy would be
best for each patient.
There's also a special situation where folks with hyperthyroidism but without known diabetes are found to have elevated BG levels. This form of diabetes will improve dramatically and may even resolve when the overactivity of the thyroid gland is successfully treated.
Typical symptoms of an underactive thyroid gland include
- weight gain
- puffy face
- cold intolerance: the opposite of hyperthyroidism -- folks with hypothyroidism turn up the thermostat, and sleep with more blankets
- dry, thinning hair
- decreased sweating
- heavy or irregular menstrual periods
- slow heart rate
Hypothyroidism is far more common that hyperthyroidism. It may occur in people with either type 1 or type 2 diabetes. As with overactive thyroid gland, women are more likely to develop hypothyroidism than are men; it's more common as you age; and it runs in families. Testing for hyperthyroidism is usually straight-forward, but different than for hyperthyroidism: the first test that is usually performed is the TSH test. If the TSH level is elevated, it's almost certain that the patient has hypothyroidism; a low level of T4 would be about all that's needed to confirm the diagnosis in most cases.
Hypothyroidism is frequently associated with elevated lipid levels, and hence with elevated risk of cardiovascular disorders such as myocardial infarction or stroke -- which is also a problem for people with diabetes. Treatment of the hypothyroidism usually causes the lipid levels to improve.
Hypothyroidism is easily treated with thyroid hormone replacement therapy, usually with synthetic T4 hormone (which is called levothyroxine; one common brand name is Synthroid). Unlike insulin therapy for diabetes, the dose that's needed is stable from day to day, and once the dose is established, it's unlikely to change. And thyroid hormone works fine when given by mouth, and only needs a once-daily dose. Rechecking the TSH level once every few months initially, then annually, is all that's usually needed to keep track of how things are
What about Graves' and Hashimoto's?
There are two autoimmune thyroid conditions that have someone's name attached to them, and that are more common in people with diabetes:
Graves' Disease is a disorder that frequently results in hyperthyroidism, bulging eyes, and goiter.
Hashimoto's Disease is a disorder that frequently results in hypothyroidism, and may have a goiter.
Both of these thyroid disorders run in families, and both may be associated with other autoimmune disorders, including (amongst others) rheumatoid arthritis, pernicious anemia, systemic lupus erythematosus, Addison's disease, celiac disease, and vitiligo.
What Should Someone with Diabetes Do?
First of all, if there's someone in your family with any kind of thyroid disorder, have your physician poke on your neck to check for goiter or thyroid nodules (this is called "palpation of the thyroid") and get your TSH level measured with the version of the test that's called the "ultra-sensitive TSH." And get it rechecked regularly.
And even if you have no symptoms, and no family history of thyroid disorders, plan to get your gland examined, and get a blood test for ultra-sensitive TSH every few years. It's not clear how often to do so, but the ADA suggests every year or two.