The thyroid gland is a small butterfly-shaped organ that exists in the front of the neck in humans. The center of this organ is located down the midline of the throat, and the two “wings” of this butterfly wrap around the windpipe. This organ is vital within the endocrine system, as it releases thyroid hormones into the blood.
These hormones are key in keeping the body healthy and functioning, as they are involved in metabolism, development and growth of the body, heat regulation, and energy, among other things. Levels of thyroid hormone released by the thyroid gland can be affected by several lifestyle factors like smoking and body mass index (BMI), diet, pollutants, and genetics.
Too much or too little thyroid hormone production can indicate thyroid dysfunction or thyroid disease. Overproduction of thyroid hormones is referred to as hyperthyroidism, and underproduction is known as hypothyroidism. Such thyroid disorders are part of a larger family called endocrine disorders, which affect the endocrine or hormone system.
Diabetes is another endocrine disorder that occurs when the pancreas either does not produce sufficient amounts of the hormone insulin or the body can’t effectively use this insulin.
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While thyroid dysfunction and diabetes are caused by imbalances in different hormones, the two endocrine disorders are still closely linked. In fact, the improper or absence of treatment of thyroid disorders can negatively affect the management of diabetes.
Hyperthyroidism can increase the heart rate, contractility, and myocardial oxygen demand — thus increasing cardiovascular risk. Insulin resistance also increases the risk. Thirdly, people with both thyroid disease and type 2 diabetes are believed to have a greater risk of coronary heart disease.
Hypothyroidism can also cause insulin to stay in the body for longer. This is because the half-life of insulin is increased and clearance from the body is reduced. It also increases low-density lipoprotein (LDL) cholesterol, which exacerbates the danger of high cholesterol and microvascular complications of diabetes.
An overabundance of thyroid hormones due to hyperthyroidism can have a significant impact on glucose homeostasis in people with diabetes and even in their healthy counterparts. Glucose homeostasis refers to the balance of the hormones glucagon and insulin, which regulate the amount of glucose in the body.¹
Glucagon increases blood sugar levels and insulin reduces them. An excess of thyroid hormone causes increased metabolism, which in turn increases lipolysis (breakdown of fat). This fat breakdown stimulates the release of insulin and glucagon, causing an abundance of these two hormones.
This increase in glucagon can lead to reduced glucose breakdown, increased blood glucose, and eventual insulin resistance. In turn, insulin resistance can cause diabetes to develop.
Therefore, it is essential that thyroid issues are regularly checked to reduce the risk of developing diabetes.
The relationship between thyroid disease and diabetes goes both ways, with the development of each disease having an effect on the other. Type 2 diabetes mellitus can also affect thyroid hormones and thyroid diseases themselves. Having type 2 diabetes can reduce thyroid-stimulating hormone (TSH) and reduce the conversion of T4 thyroxine to triiodothyronine (T3) in peripheral tissues.
This means that circulating thyroid hormones are lower and individuals may suffer the many symptoms of hypothyroidism. If type 2 diabetes is left untreated, it can lead to resistance to insulin, which can cause the proliferation of tissue in the thyroid gland.
Such proliferation vastly increases the risk of thyroid nodule development and inflammation of the thyroid gland itself, leading to goiter. This can exacerbate the negative impact of both diabetes and thyroid disease.
Certain antidiabetics, such as sulfonylureas, pioglitazone, and thiazolidinediones, can also negatively alter thyroid functioning.
Some researchers report that this leads to higher incidences of thyroid cancer in patients taking glucagon-like peptide (GLP)-1 receptor agonists, which are used to treat diabetes. However, it’s important to note that the research isn’t currently strong enough to discourage people with diabetes from taking their regularly prescribed medications.²
Another reason for the highly interwoven nature of diabetes mellitus and thyroid dysfunction is the link between hyper- and hypothyroidism and insulin resistance. As mentioned, the thyroid hormone is essential for metabolism in humans, including the metabolism of carbohydrates and sugars.
For this reason, the imbalance of thyroid hormone can actually impact insulin levels, leading to many issues, including the development of type 2 diabetes. An excess of thyroid hormone (hyperthyroidism) can cause increased lipolysis, which results in an overabundance of free fatty acids in the blood.
These high levels of free fatty acids can reduce the secretion of insulin, causing resistance to the hormone and diabetes. Animal studies have also confirmed the relationship between insulin resistance and hyperthyroidism.³
Hypothyroidism is also associated with insulin resistance. Researchers posit that the lack of thyroid hormone reduces the ability of insulin to utilize glucose in the working muscles. Reductions in metabolism associated with hypothyroidism also mean that insulin isn’t broken down as quickly as it is in healthy patients. This means that insulin remains in the blood for longer periods.
In the general population, hypothyroidism is a rather common condition, with estimates that around 5% of the population have it (with a possible additional 5% undiagnosed). Hyperthyroidism, on the other hand, is estimated to occur in 1.3% of American individuals and 0.8% of European individuals.⁴ ⁵
Thyroid-related conditions are almost ten times more common in women than men. Certain diseases illustrate this relationship; studies suggest that 1% of men and 5% of women have thyroid nodules. These relationships are exacerbated by age and lack of iodine in the diet.
When we consider populations of individuals with diabetes, this number skyrockets. Research has found that around 17–30% of adult patients with type 1 diabetes also have autoimmune thyroid dysfunction. In children, around 25% of those with type 1 diabetes also have autoimmune hypothyroidism.⁶
This dysfunction is also more common in type 2 diabetes patients than in the general population.
Both diabetes and thyroid disorders can be autoimmune in origin, which means the body’s immune system begins to attack itself. In the case of thyroid conditions, the immune system attacks the thyroid gland, causing Hashimoto’s disease (which causes hypothyroidism) or Graves’ disease (which causes hyperthyroidism). In diabetes, the immune system attacks the beta cells in the pancreas, which are the cells that produce insulin.
This causes the type 1 variant of diabetes. As autoimmune disorders occur due to dysfunction of the immune system, once one condition has developed, the immune system is more likely to continue to attack different organs within the body.
Researchers even suggest that a link exists between the autoimmune functions that underlie type 1 diabetes and thyroid disorders, including autoimmune thyroiditis, hypothyroidism, and Graves’ disease.⁷
In general, the risk of developing a thyroid condition is higher in certain populations. These include women, people over 60, people with a family history of thyroid issues or autoimmune conditions, and people with either high or low amounts of iodine in their diet.
Risk factors for type 1 diabetes include having a family history of type 1 diabetes and a genetic predisposition for the disease. People at higher risk for developing type 2 diabetes include those who have prediabetes, who are 45 years old or older, are overweight, those with a close relative with type 2 diabetes, and those taking part in less than three days of physical activity a week.
Research has found an association between autoimmune thyroid disease and type 1 diabetes, with an increased risk present for thyroid autoimmunity in patients with pre-existing type 1 diabetes.
Poorly controlled diabetes in children can also prompt hypothyroidism later in life. A genetic link between autoimmune thyroid disease and type 1 diabetes has also been established, with researchers revealing at least four genetic factors that underlie both disorders.⁸
Thyroid issues can arise due to over- or underproduction of the thyroid hormones, which can cause a variety of issues. Perhaps the most commonly considered thyroid diseases are hypothyroidism and hyperthyroidism.
Hypothyroidism, or underactive thyroid, occurs when insufficient levels of thyroid hormone are produced by the thyroid gland. This can cause several symptoms, including weight gain, tiredness, dry skin, issues with regulating temperature in the cold, and irregular menstrual periods. It tends to slow the metabolism and makes normal body functioning difficult.
Hyperthyroidism, however, occurs when the thyroid gland is overactive and secretes too much thyroid hormone. This can result in many troubling symptoms, including excessive weight loss, irregular heartbeat, heat intolerance, shaky hands, and muscle weakness. Hyperthyroidism tends to increase metabolism and speed up many of the body’s processes.
A variety of other common thyroid diseases exist, including:
Hashimoto’s disease. This condition is autoimmune in nature, where the immune system attacks and damages the thyroid gland, leading to dysfunction.
This often means the gland is less able to secrete thyroid hormone, leading to lower circulating levels of thyroid hormone and possibly hypothyroidism. In some very rare cases, Hashimoto's disease can cause overstimulation of the remaining areas of the thyroid and increase thyroid hormone secretion.
Graves’ disease. Graves’ disease is another autoimmune thyroid condition; however, it commonly causes overproduction of thyroid hormone and hyperthyroidism.
This is perhaps the most physically obvious of the thyroid conditions, as those with Graves’ disease have a rather obvious swelling of the neck over the thyroid gland. This protrusion is characteristic of Graves’ and is often accompanied by swelling of the tissue around the eyes, causing them to bulge or protrude from their sockets. This can cause significant visual impairment if not treated.
Thyroid nodules. Thyroid nodules are growths occurring on the thyroid gland. These can be cancerous or benign; however, both conditions can be rather serious, as they may cause distressing symptoms, such as voice or swallowing problems. Thyroid nodules may require a thyroidectomy (removal of the thyroid gland). In rare cases, these nodules may stimulate the thyroid gland, leading to overproduction of the thyroid hormone and, in some cases, hyperthyroidism.
Many studies have demonstrated an extensive link between hyperthyroidism and diabetes; this link may be due to a multitude of reasons. One is the effect of thyroid hormones on metabolism.
In children with type 1 diabetes, researchers have found a link between elevated blood levels of thyroid-stimulating hormone (TSH) and glycolipid metabolism. These researchers have proposed that the amount of TSH circulating in the blood may be a good indicator of the severity of diabetes.⁹
It’s important to note that Graves’ disease is an autoimmune condition that commonly causes hyperthyroidism and is closely associated with the development of type 1 diabetes.
A similar association has been found for Hashimoto’s disease, with experts reporting that around 17% of patients with this condition also have type 1 diabetes. This may be due to the aforementioned autoimmune link.¹⁰
Having hypothyroidism increases one’s risk of developing a range of conditions, including type 2 diabetes. As this condition tends to slow the metabolism down, people are less able to properly process their food to turn it into energy that can be used.
This means a lot of the food they intake is stored as fat, which increases the likelihood of developing conditions such as metabolic syndrome and type 2 diabetes.
Researchers have indicated that clinicians should be aware of the link between diabetes and hypothyroidism. They state that this relationship is especially obvious in cases of type 1 diabetes. It’s possible this link may be strengthened by an underlying autoimmune condition of both diseases.¹¹
Factors stimulating the relationship between thyroid disease and type 2 diabetes, however, may be due to a lack of dietary iodine and poor glycemic control.
It’s clear that hypothyroidism has a wide branching effect on metabolism, with some researchers suggesting that it can also affect blood sugar levels.¹²
It’s been established that patients with comorbid hypothyroidism and diabetes have higher levels of hemoglobin A1C, which is a measure of the amount of blood sugar in diabetes patients. As higher levels of A1C indicate poor management of diabetes, this may indicate the presence of hypothyroidism, which can worsen the A1C control.
Prediabetes is a rather common condition where people have elevated blood sugar without it reaching the levels for clinical diagnosis of diabetes.
It’s a serious condition that increases the risk of a person encountering cardiovascular issues and developing type 2 diabetes. As thyroid dysfunction increases the risk for type 2 diabetes, screening for thyroid disorder in patients with hyperglycemia may be useful.
A recent study also suggests that anyone with any form of diabetes should be screened for issues with their thyroid. This can help these people to better manage and treat their symptoms, facilitating an easier life with more manageable symptoms.¹³
Although an individual may not be able to prevent the development of type 1 diabetes or thyroid disorders, one can prevent type 2 diabetes. As type 2 diabetes tends to be less linked to genetics than its type 1 counterpart, it can be prevented by weight loss, physical activity, and eating a balanced and healthy diet.
This prevention can occur even when a person is prediabetic. If diabetes does end up developing, its symptoms can be at least partially reduced to prevent the disorder from worsening. Management strategies include knowing the diabetes “ABCS”:
A: A1C test. This is a test that demonstrates your blood glucose level from the last three months. This allows an individual to set a goal (usually below 7% blood glucose) and work towards maintaining it.
B: Blood pressure. It’s important to keep your blood pressure down. While every person with diabetes is different, the recommended blood pressure is below 140/90 mm Hg.
C: Cholesterol. The goal of diabetes management is to reduce the amount of “bad cholesterol”, or LDL, in the blood. This can cause blood vessel clogging and a range of cardiovascular issues such as heart attacks. It’s also helpful to increase the amount of “good cholesterol,” or high-density lipoprotein (HDL), in the blood as this can help reduce the LDL. Such cholesterol modulations can be achieved by dietary changes.
S: Stop smoking. While quitting smoking is a healthy choice for anyone, stopping smoking can be especially helpful in cases of diabetes, as smoking narrows the blood vessels. Diabetes also narrows the blood vessels, which means the heart has to work harder and affected people are more at risk of cardiovascular issues.
A range of other factors can also help people manage diabetes, like setting up a meal plan with your healthcare professional, increasing physical activity levels, regularly checking blood glucose levels, and taking your prescribed medicines.
Treatment of thyroid disorders varies depending on the type of thyroid disease.
In hyperthyroidism, people can be given drugs to reduce the levels of thyroid hormones in their blood; receive radioactive iodine treatment, which destroys thyroid gland cells to reduce thyroid hormone secretion; or undergo surgery to remove a portion of the thyroid gland. Beta-blockers can also be taken to treat symptoms of hyperthyroidism.
Hypothyroidism is currently incurable; however, it can be completely managed in most patients. This is done by artificially replacing thyroid hormones in the bloodstream by taking certain medications such as levothyroxine. This medication is a synthetic version of the thyroid hormone and helps restore the body's thyroid function to healthy levels and mitigate symptoms.
If you have any doubts about your health, you should visit a medical professional immediately.
In the case of diabetes, if you’re experiencing any of the following symptoms, it may be time to seek professional help:
Increases in thirst and hunger
More infections than usual and slowed wound healing
Unintentional weight loss
Numbness or tingling in your hands and feet
Hypothyroidism can present in many ways, and if you experience any of the following, it may be time to visit your healthcare professional::
Sensitivity to the cold
Loss of sex drive
Numbness or tingling in the hands
Muscle cramping and weakness
Hyperthyroidism has a different symptom profile that includes the following indicators:
Sensitivity to heat
Nervousness or anxiety
Loss of sex drive
Although some overlap exists between these conditions, if any of the above symptoms match those that you or a loved one are experiencing, you should seek medical help. Early detection of diabetes or thyroid dysfunction can help with the management and even with possibly curing the disorder in some cases.
Diabetes can be screened and tested for diagnosis in many ways. The screening method used depends on the healthcare professional's choice and the presentation of symptoms. Some screening and tests include:
A1C testing. Measuring the average blood glucose from the past three months. Normal levels of blood glucose are < 5.7%, prediabetes hovers between 5.7 and 6.4%, and clinical diabetes is characterized by blood glucose levels of 6.5% or higher.
Fasting plasma glucose (FPG). This test usually occurs in the morning as people are required to fast (not eat or drink) for at least eight hours before testing. This test, as the name suggests, measures the blood glucose levels when an individual is in a fasting state. Healthy individuals have a blood glucose level of < 100 mg/dl, people with prediabetes present with 100–125 mg/dl, and those with diagnosable diabetes have an FPG of 126 mg/dl or higher.
Oral glucose tolerance test (OGTT). This test involves measuring blood glucose just before and two hours after the consumption of a sweet drink. This test is designed to tell the clinician how well your body processes glucose. Healthy individuals should have less than 140 mg/dl after the two hours, people with prediabetes should have levels of 140–199 mg/dl, and people with diagnosable diabetes will have levels of 200 mg/dl or higher after the two hours have elapsed.
Random/casual plasma glucose test. In this test, blood is taken when the individual has severe diabetes symptoms. Blood glucose levels must be at 200 mg/dl or higher for diagnosis.
Hyperthyroidism is usually screened for using a blood test that checks levels of thyroid hormone in the blood. This is called a thyroid function test and checks the levels of TSH, triiodothyronine (T3), and thyroxine (T4). The first hormone is a pituitary hormone that regulates the production of thyroid hormone, and the latter two are the main thyroid hormones.
Levels of such hormones are compared to the healthy normal levels to determine if the thyroid is overactive. Further blood testing can also be conducted; this is less common but includes testing for the following:
Antithyroid antibodies (common in Graves’ disease)
Erythrocyte sedimentation (ESR) for inflammation (a possible sign of thyroiditis)
Thyroid scan (to check for gland abnormalities)
The thyroid function test is also performed for hypothyroidism, where the aim is to examine if thyroid hormone levels are lower than the healthy normal. If the clinician suspects your thyroid issue may be thyroiditis/Hashimoto's thyroiditis, additional testing may be needed.
Hypothyroidism can be treated with a medication called levothyroxine. This drug functions to increase thyroid hormone levels in the blood. It’s a synthetic form of the hormone thyroxine, which the thyroid gland struggles to produce in cases of hypothyroidism.
It works immediately; however, symptoms may still be present after a few weeks. If you’re experiencing hypothyroidism, your doctor will prescribe the appropriate dose of this medication if you are able to take it.
This may help to better regulate your metabolism, which may reduce the likelihood of you developing diabetes or reduce the symptoms if diabetes is already present.
Hyperthyroidism can be treated with a variety of medicines called thionamides or antithyroid medication. These function to reduce the secretion of thyroid hormones by the thyroid gland. The most common forms of this medication are carbimazole and propylthiouracil.
A highly interwoven relationship is present between diabetes and thyroid disease, possibly due to alterations in glucose metabolism, autoimmunity, insulin, or other factors. It’s important that clinicians and patients alike are aware of this link and work hard to monitor both conditions if they’re present.
Glucose homeostasis | Science Direct
Hypothyroidism | American Thyroid Association
Diabetes | World Health Organization
Type 1 diabetes | National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
What are common symptoms of autoimmune disease? | Johns Hopkins Medicine
Are you at risk for thyroid disease? | Everyday Health
Diabetes risk factors | Centers for Disease Control and Prevention
Hypothyroidism (underactive thyroid) | National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Hyperthyroidism (overactive thyroid) | National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Hashimoto's disease | National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Graves’ disease | National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
What are thyroid nodules? | Endocrine Web
Thyroid nodules: When to worry | Johns Hopkins Medicine
The surprising truth about prediabetes | Centers for Disease Control and Prevention
Prevent type 2 diabetes | Centers for Disease Control and Prevention
Managing diabetes | National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Hyperthyroidism (overactive) | American Thyroid Association
Radioactive iodine (Radioiodine) therapy for thyroid cancer | American Cancer Society
Hypothyroidism (underactive) | American Thyroid Association
Diabetes symptoms | Centers for Disease Control and Prevention
Diagnosis | American Diabetes Association
Thyroiditis | NHS