There’s a butterfly-shaped gland that nestles in your lower neck, straddling the windpipe. It’s called the thyroid, and its job is to ramp up or dial down the rate at which the body uses energy from food, as directed by the brain. Sometimes the thyroid malfunctions, leading to disease. People with diabetes, both type 1 and type 2, are more prone to thyroid disease than the general population. And that is of particular concern because thyroid disease complicates blood glucose control.

The Thyroid and Diabetes
The thyroid is the largest gland in the endocrine system, a network that regulates important biological processes like growth, development, and metabolism. The gland can produce hormones telling the body to burn energy quickly, boosting metabolism, or withhold these hormones, slowing the body’s activity down. Like diabetes, thyroid disease is caused by a hormone imbalance, although the hormones involved are different. Thyroid disorders are typically related to either an overproduction of thyroid hormones (hyperthyroidism) or, more commonly, an underproduction (hypothyroidism).

About 7 percent of the population has some type of thyroid disease; it’s more common in women than in men. Among people with type 2 diabetes, that proportion increases to about 12 percent, and people with type 1 have up to a 1-in-3 chance of developing a thyroid disorder.

Like type 1 diabetes, some forms of thyroid disease are autoimmune disorders, attacks against some part of the body by one’s own immune system. A person with one autoimmune disease is more likely to get another. In type 1, the immune system attacks the cells in the pancreas that make insulin. In some types of thyroid disease, the immune system attacks the cells of the thyroid.

The link with type 2 diabetes is less clear, but some experts think it may have to do with aging. Like type 2, thyroid disease is more common among older adults. Some doctors recommend that women over 50 be screened for the disease. Another possible association has to do with weight: Hypothyroidism can cause weight gain, which is in turn associated with type 2 diabetes.

Totally Hormonal
Because of the high risk of thyroid disease among people with type 1 diabetes, it’s especially important for them to get tested. The American Diabetes Association recommends that everyone with type 1 be tested for hypothyroidism at diagnosis and, if the initial exam is normal, every year or two afterward. Testing isn’t thought to be necessary for everyone with type 2 because the risk of thyroid disease is less. However, it’s wise to be familiar with its symptoms so you can detect hormone abnormalities early before blood glucose levels worsen. During pregnancy, hormone changes can trigger thyroid disease, which can endanger the fetus. Safe treatments are available. There is no consensus on whether all pregnant women should be screened for thyroid disease, but those at high risk, including women with type 1, should be tested. Women with thyroid disease who want to get pregnant should check with their doctors to make sure it’s safe and be monitored carefully during pregnancy.

A simple blood test can detect thyroid disease. The test measures levels of a hormone from a gland in the brain that signals the thyroid to produce hormones. Too much of the thyroid-stimulating hormone, or TSH, indicates hypothyroidism; the pituitary gland overproduces TSH to compensate for a thyroid that isn’t producing enough of its hormones. On the other hand, if TSH is scarce, it’s likely that the thyroid is making too much hormone and causing hyperthyroidism.

The symptoms of hypothyroidism and hyperthyroidism are about what one would expect from diseases that decrease and increase metabolism, respectively. Hypothyroidism is associated with fatigue, lethargy, depression, constipation, weight gain, low blood pressure, a slow pulse, and intolerance to cold. Conversely, hyperthyroidism may cause sweating, weight loss, diarrhea, distraction, menstrual changes in women, rapid heart rate, and thick skin on the knees, elbows, and shins. Both untreated hypothyroidism and hyperthyroidism may cause the thyroid gland to become abnormally large, a condition called goiter. Sometimes thyroid dysfunction is “subclinical,” meaning that TSH levels are only slightly out of range and thyroid hormones are at normal levels. However, these mild forms can still cause problems, and some doctors will treat subclinical cases with medication.

Double Duty
Thyroid disease can make blood glucose control more difficult in part because of its effects on medication in the body. A pumped-up metabolism from hyperthyroidism can cause diabetes and other medications to be eliminated from the body too quickly, reducing their effectiveness. So, people with diabetes and hyperthyroidism may need higher doses of insulin or oral medications. With hypothyroidism, the opposite is true: Medications tend to linger in the system, and there is a risk of overmedication. In diabetes, that could cause low blood glucose (hypoglycemia).

Hypothyroidism can be treated with a synthetic version of thyroid hormone. For people with hyperthyroidism, treatment options include antithyroid medications, radioactive iodine that destroys thyroid cells, and surgery to remove some or all of the thyroid gland.

Having two endocrine diseases may seem like double trouble, but diabetes and thyroid disease can be effectively controlled by adjusting treatments for both. A properly tuned thyroid can keep the body’s metabolism humming along at a steady clip, and that can greatly help people with diabetes stay healthy.