Thyroid Disorders and Type 1 Diabetes
Autoimmune problems with this small but important gland
“Common things occur commonly” is an old medical school adage used to remind future doctors that two common diseases will frequently overlap but aren’t necessarily related. The link between type 2 diabetes and thyroid disease is a perfect example of this, says Peter Arvan, MD, PhD, professor of internal medicine and chief of the Division of Metabolism, Endocrinology, and Diabetes at the University of Michigan.
In the United States, nearly 28 million people have type 2 diabetes and 20 million have some form of thyroid disease. This means that people with type 2 diabetes frequently have thyroid disease as well. But type 2 does not increase your risk for thyroid disease (for more on that, see “What About Thyroid and Type 2?” below).
People with type 1 are even more likely to have thyroid problems, even though type 1 doesn’t directly cause thyroid disease. According to the American Diabetes Assocation’s 2016 Standards of Medical Care in Diabetes, autoimmune thyroid disease occurs in 17 to 30 percent of people with type 1. The main issues? Hyperthyroidism, which happens when the body produces too much thyroid hormone, and hypothyroidism, which occurs when your body does not produce enough.
The thyroid is a butterfly-shaped gland in the neck that produces two hormones, triiodothyronine, also known as T3, and thyroxine, or T4, which regulate your metabolism. “[It’s] sort of like the body’s furnace,” Arvan says. In addition, the thyroid affects brain development, breathing, heart and nervous system function, body temperature, muscle strength, skin dryness, menstrual cycles, weight, and cholesterol levels.
While the thyroid produces the hormones, the brain’s pituitary gland is the mastermind behind thyroid hormone production and regulates hormone release with thyroid-stimulating hormone, or TSH. When blood levels of the thyroid hormones are low, the pituitary gland releases more TSH to spur the thyroid into action. When hormone levels are high, the pituitary gland decreases TSH production.
Many different things can cause hyperthyroidism and hypothyroidism, but in people with type 1 diabetes, the root cause is typically an autoimmune problem, says Arvan. People whose genes make them susceptible to autoimmune diseases will frequently develop more than one.
“The immune system doesn’t recognize the beta cell [in the pancreas] or the thyrocyte [in the thyroid] as belonging to self, and so they are attacked,” says R. Mack Harrell, MD, medical imaging director at the Memorial Center for Integrative Endocrine Surgery and past president of the American Association of Clinical Endrocrinologists, noting that occasionally there’s crossover—the immune system attacks several parts of the body.
- Hyperthyroidism—The most common cause of an overproduction of thyroid hormone in people with type 1 is Graves’ disease, says Peter Singer, MD, a professor of clinical medicine and director of the Thyroid Diagnostic Center at the University of Southern California’s Keck Hospital. Graves’ disease is an autoimmune disorder that causes the body to produce an antibody, called thyroid-stimulating immunoglobulin (TSI), that overrides the normal regulation of the thyroid. This causes too much thyroid hormone to be produced.
Symptoms—You may have an increased heart rate and heart palpitations. Because your metabolism speeds up, you may feel warm, lose weight, or have difficulty falling asleep. “You feel amped up,” says Singer. “Like if your car has six cylinders, you may feel like you’re on eight cylinders.”
- Hypothyroidism—Hashimoto’s disease is also an autoimmune disorder common in people with type 1 diabetes. In fact, Hashimoto’s disease is the most common cause of hypothyroidism in the United States. In this case, the immune system attacks the thyroid gland, which interferes with its ability to produce enough thyroid hormone for the body.
Symptoms—You may feel cold; have a slow heart rate; gain weight; experience fatigue, sluggishness, or an increased desire for sleep; become constipated; or notice your hair is thinning and dry. In the same car analogy, Singer says, “instead of six cylinders, you feel like you have four.”
Three common blood tests can measure blood levels of either the thyroid hormones (T3 and T4) or thyroid stimulating hormone (TSH). Several other tests can be done if Graves’ disease is suspected, such as a radioactive iodine uptake test, a thyroid scan, or a TSI antibody test. If Hashimoto’s disease is a possibility, another antibody test, called an antithyroid antibody test, is available.
Such tests can determine if you have antibodies—molecules produced by your own body that attack the thyroid—present in your blood. These antibodies are typically found in people who have autoimmune forms of hyperthyroidism and hypothyroidism, but not always.
- TSH test—Typically the first test used to see how the thyroid is working, this is considered the most accurate test for diagnosing thyroid dysfunction. Because TSH is released by the pituitary gland to stimulate the production of thyroid hormones, low test results (under 0.4 mIU/L) indicate hyperthyroidism. When test results are high (over 4.0 mIU/L), hypothyroidism is suspected.
- T4 test—To add information to TSH test results, T4 tests are often performed. The T4 test measures the level of thyroxine hormone in your blood. Thyroxine is the main hormone produced by the thyroid. The normal range for test results is 4.5 to 11.2 mcg/dl. A higher-than-normal level can mean hyperthyroidism and a lower-than-normal level can indicate hypothyroidism.
- T3 test—In some cases of hyperthyroidism, T3 is produced in excess and T4 results can appear normal despite an overactive thyroid. That’s why the T3 test is helpful in confirming hyperthyroidism. This test measures triiodothyronine in the blood. Normal test results will fall between 100 and 200 mg/dl. Higher-than-normal results indicate hyperthyroidism while lower-than-normal results can point to hypothyroidism.
As in type 1 diabetes, the body also produces thyroid antibodies that can be detected in the blood when an autoimmune reaction is occurring in the body, says Arvan. The two most common antibodies associated with hypothyroidism, anti-TPO and anti-TG, can increase the likelihood that someone will develop the disease. They each attack a different protein in the thyroid and can be useful in diagnosing Hashimoto’s disease.
The antibody associated with hyperthyroidism—thyroid-stimulating immunoglobulin—and thyroid receptor antibodies can also be detected in the blood and can help diagnose Graves’ disease.
While antibodies can indicate a higher risk for certain autoimmune diseases, they don’t guarantee that you have the disease or that you’ll definitely get it at some point in your life. But, Arvan says, while having more than one antibody does increase the possibility, “we can make predictions about your risk,” he says, but can’t yet prevent the disease from developing.
If you have more than one autoimmune disease, such as type 1 diabetes and Hashimoto’s disease, you’re more likely to develop even more autoimmune problems, says Arvan. These can include alopecia (hair loss), lupus, pernicious anemia (a decrease in red blood cells from the inability to absorb vitamin B12), premature ovarian failure, celiac disease, and vitiligo (a disorder that causes white spots on the skin).
When it comes to hypothyroidism, treatment is pretty easy—one simple pill. “If you don’t make enough thyroid hormone, we’re lucky we have a tablet that replaces it, called thyroxine,” says Singer. Thyroxine is a synthetic form of T4 and is usually taken once a day.
Hyperthyroidism is a bit trickier, but there are anti-thyroid medications available to help lower the levels of thyroid hormone in the blood. “You may try to achieve a remission [with medication],” says Singer. “But in the United States, only about a third of people will be cured with medication.”
For those people who don’t respond to medication, radioactive iodine is used instead. That obliterates the thyroid, and then they end up having to take thyroxine, says Singer.
While radioactive iodine sounds scary, it’s generally safe and has few side effects, which can last from a couple of days to a few weeks. Women who are or want to become pregnant in the near future cannot take it because the treatment may affect the fetus. Surgery to remove the thyroid is recommended instead. “Once they [have] surgery, they can get pregnant right away,” Singer says.
Food and medication interactions can also become an issue when you have to take synthetic thyroid hormone. “Patients with diabetes have enough issues with managing calories and food, but when they have thyroid disease thrown in, they have new issues,” says Harrell. Case in point: Thyroid hormone does not mix well with calcium, soy, and iron.
Certain medications, such as Carafate for the treatment of gastritis, can impair the absorption of thyroid hormone because they coat the stomach. If you are taking Warfarin or anticoagulants, you may need to adjust your dose because the medications can alter your thyroid hormone levels. It’s best to have a thorough conversation with your doctor and pharmacist about any possible interactions to figure out how to best manage both diabetes and thyroid disease.
Type 1 diabetes is a risk factor for thyroid disease, so screening for thyroid problems is recommended in people with the disease. According to the 2016 American Diabetes Association Standards of Care, a TSH test is recommended for people with type 1 diabetes at diagnosis and after if symptoms are present, in those with high cholesterol and/or triglycerides, and in women over 50. Children should be tested for thyroid-related antibodies soon after being diagnosed with type 1 diabetes. A TSH test should also be performed. With normal test results, children should be re-checked every one to two years—or sooner if they develop symptoms of thyroid dysfunction. To prevent inaccuracies, thyroid levels must be measured when blood glucose is stable.
Women with type 1 should get special attention, says Harrell, because women in general are three to four times more likely to develop thyroid issues than men. It’s also important to screen for and treat thyroid disease before a woman with type 1 attempts to become pregnant.
- Increased heart rate
- Fluttering or pounding heart
- Unexplained weight loss
- Sensitivity to heat/sweating
- Difficulty sleeping
- Swelling at the base of the neck
- Unexplained weight gain
- Sensitivity to cold
- Slow heart rate
- Thinning hair
What About Thyroid and Type 2?
For the most part, type 2 diabetes and thyroid disease overlap because they are two of the most common endocrine diseases in the United States, says R. Mack Harrell, MD, medical imaging director at the Memorial Center for Integrative Endocrine Surgery and past president of the American Association of Clinical Endocrinologists.
One exception is that hypothyroidism causes weight gain, which can possibly lead to insulin resistance and eventually type 2 diabetes, says Peter Arvan, MD, PhD, professor of internal medicine and chief of the Division of Metabolism, Endocrinology, and Diabetes at the University of Michigan. “People with hypothyroidism can definitely secondarily have either worsening preexisting diabetes or even development of new type 2 diabetes.”
- Weight Expectations
If you’re hoping to be prescribed a large dose of artificial thyroid hormone to treat hypothyroidism and stimulate major weight loss, you may want to pump those brakes. “The usual person who comes in with hypothyroidism and gets put on a thyroid hormone preparation does not lose that much weight—maybe 5 to 10 pounds at most,” Harrell says. While this may be frustrating, he says increasing the thyroid hormone dose is not a good idea. Too much thyroid hormone in the body can lead to an irregular heartbeat and bone loss—“both of which end up being worse in the long run than being a few pounds overweight,” he says.
- Metformin Concern
Some research has shown that metformin, often the first drug used to treat type 2 diabetes, may interrupt thyroid function and have some effect on TSH levels in the blood. But the effect is minimal and would likely not make a difference, says Peter Singer, MD, professor of clinical medicine and director of the Thyroid Diagnostic Center at the University of Southern California’s Keck Hospital. “In my view, it’s trivial, insignificant, and would not affect control.”
Because certain foods interfere with its absorption, thyroid hormone should be taken first thing in the morning on an empty stomach, about 45 minutes to an hour before eating. It’s best to avoid taking other medications at the same time—some can affect thyroid hormone absorption, including:
- Aluminum hydroxide
- Calcium carbonate
- Iron sulfate
- Lanthanum carbonate
Omeprazole and lansoprazole, both used to treat gastroesophageal reflux disease (GERD), may affect gastric acid production, which can change how thyroid hormone is absorbed. You can still take those drugs with thyroid hormone, but if you start or stop the meds during thyroid hormone therapy, you may need to change your dose. Other medications that impair acid secretion may also interfere with T4 absorption, as can syndromes that impair absorption, such as celiac disease.