Medically reviewed by
Dr. Minako Abe, M.D., Board-certified emergency medicine physician researching the relationship between lifestyle and disease onset in relation to the immune system and cancer, Japan
Your endocrine system consists of several glands that work together to produce hormones that cells use to communicate with each other. When this system becomes disrupted, you encounter problems with getting pregnant, managing your stress, weight gain, lack of energy, puberty, or increases in your blood sugar. Your thyroid gland is responsible for hormone production for processes such as metabolism, growth, and development. Hormones enter the bloodstream and respond to your body’s needs.
For example, if you’re outside shoveling the snow for a long time, your body gets colder and your thyroid gland responds by producing more hormones. Diabetes mellitus, otherwise known as diabetes, and thyroid diseases are very common endocrine disorders that are closely linked, and therefore influence each other. In other words, it is extremely common for individuals to experience both conditions together. However, today, clinical settings are developing screening methods and management to identify the conditions before they progress too far and have created treatments to aid those affected by the disorders.
What is Diabetes?
According to the World Health Organization, in 2019, diabetes directly caused 1.5 million deaths with 48% being before the individual reached 70 years old. However, raised blood glucose levels are responsible for nearly 20% of cardiovascular deaths. Diabetes is scientifically coined as Diabetes mellitus which encapsulates many metabolic conditions related to hyperglycemia.
Hyperglycemia (hyper means high, glykys meaning sugar or sweet, and emia meaning blood) is when your blood glucose levels are higher than normal. It is a common characteristic of diabetes as it shows that your body is not properly using or producing insulin, and allowing glucose to accumulate in your blood.
Insulin is produced by your pancreas and helps transport glucose to where it is needed most, often to your muscle cells. When you eat carbohydrates, your body converts them into glucose and enters the bloodstream. Simply, insulin turns glucose into a usable form of energy for your body! You need glucose for energy when it is in a healthy range, but when you become chronically hyperglycemic, you are put at higher risk of microvascular complications or dysfunction including neuropathy, nephropathy, and retinopathy.
According to the Centers for Disease Control and Prevention (CDC), fasting blood sugar (taken after not eating overnight or after 8 hours) around 99 mg/dL is considered normal. 100 to 125 mg/dL can indicate prediabetes, while 126 mg/Dl and above is a diagnosis of diabetes.
Classifications of Diabetes
Diabetes is classified into four major categories. Type 1 and type 2 are the most commonly recognized while the other two categories include gestational diabetes and other specific types of diabetes.
Type 1 diabetes is immune-mediated (making it a chronic autoimmune condition) where pancreatic beta-cells are destroyed by your autoimmune inflammatory mechanisms leading to insulin deficiency. When you’re not producing insulin, your cells can not function properly and glucose begins to accumulate in your bloodstream.
Type 2 diabetes is characterized as a metabolic disorder caused by beta-cell dysfunction. Around 95% of people with diabetes will have type 2 diabetes. Unfortunately, type 2 diabetes has increased in frequency in children over the past few years as it is most often caused by obesity and sedentary lifestyles. Type 2 diabetes is recognized by insulin resistance and glucagon suppression in the body.
Gestational diabetes (GDM) also known as carbohydrate intolerance is commonly seen in pregnancy but will typically recede after the baby is delivered. Gestational diabetes is recognized as hyperglycemic and is one of the most common complications of pregnancy. Dietary changes and physical exercise are often encouraged, but when normoglycemia is not reached, then pharmacotherapy likely with insulin is used.
Other types of diabetes may be termed as “secondary-diabetes” more related to pancreatic diseases or mutations in certain beta-cell and hepatic genes.
Association Between Diabetes mellitus and Thyroid Disorders
Thyroid dysfunction (TD) affects around 6.6% of adults in Europe and the United States. The risk of TD increases with age and is categorized as hyperthyroidism or hypothyroidism at severe or subclinical levels. For example, subclinical forms of thyroid disease such as subclinical hypothyroidism (SHypo) occur when your serum thyroid-stimulating hormones (TSH) are mildly elevated. At the same time, your peripheral thyroid hormones levels are normal. In subclinical hyperthyroidism (SHyper), your serum TSH levels would be lower than average. While asymptomatic, both conditions have adverse effects when left undiagnosed.
Diabetes and thyroid disorders often coexist in patients as both disrupt the endocrine system and the formation of hormones. Consequently, their biggest impact is on the control of glucose production and blood sugar levels. One study found that 17% to 30% of adults with type 1 diabetes were also diagnosed with autoimmune thyroid disease (AITD), an organ-specific autoimmune disease that contributes to hypothyroidism or hyperthyroidism. The higher prevalence of thyroid disorders in diabetic patients has been studied globally. In Saudi Arabia, 16% of type 2 diabetic patients were found to also have thyroid disorders. Another study found that type 1 diabetes developed in thyroid disorders much earlier than in the general population leading to 25% of type 1 diabetics in children also being diagnosed with autoimmune hypothyroidism. The co-occurence of both conditions may result in hypoglycemia, which may be due to decreased insulin requirement paired with increased insulin sensitivity. Nearly 50% of AITD patients also show signs of glucose intolerance.
To summarize, you require consistent hormone production to activate and regulate biological processes such as carbohydrate metabolism, pancreatic function, and growth. When hormone production is disrupted by thyroid diseases, it can cause conditions such as hyperthyroidism and hypothyroidism which can increase an individual’s diabetic risk. On the other hand, diabetes affects thyroid function and can lead to hormone disruption and further thyroid complications.
Diabetes Increases Risk for Thyroid Cancer
Many studies hypothesize a link between diabetes and an increased risk for thyroid cancer. This is due to the higher prevalence of thyroid disorders in diabetic patients compared to the general population. A primary finding concluded that mild, chronic TSH elevation, a major risk factor for thyroid cancer, was commonly seen in diabetic patients. This positive association between diabetes and thyroid cancer was more common in women.
Another study found that type 2 diabetes is linked to a higher risk of cancers such as lung cancer, pancreas cancer, and thyroid cancer. While the association between diabetes and a higher risk for cancer is still fairly new, there is potential for improving the diagnosis of thyroid disorders with the current understanding of diabetes.
Next Steps in Healthcare
Annual thyroid testing in diabetic patients may help detect the risk of thyroid dysfunction; however, the diagnosis process is difficult as diabetes can mask the symptoms of TD. It is known that hyperthyroidism increases hyperglycemia. Hyperglycemia is basically high blood glucose or blood sugar. The underlying scientific mechanism for this involves the stimulation of glucose production and increased expression of GLUT2 glucose transporters.
Alongside other mechanisms including the upregulation of gluconeogenesis, hyperthyroidism increases the absorption of glucose in the gastrointestinal tract. In other words, gluconeogenesis is how your body produces glucose and by working with hyperthyroidism, more glucose is absorbed by your GI tract which increases your overall blood sugar. This is why many diabetic patients with hyperthyroidism will find it difficult to control their blood glucose.
On the other hand, hypothyroidism masks the symptoms of diabetes as it decreases the formation of glucose by the liver. This would mean diabetic patients with hypothyroidism would require less insulin compared to other diabetics. Unfortunately, due to a lack of agreement regarding normal thyroid hormone levels and treatment of thyroid disorders being necessary in some cases, thyroid disease screening in diabetic patients is not recommended globally, despite its benefits.
According to the 2015 National Institute for Health and Care Excellence (NICE) guidelines for type 2 diabetes, monitoring thyroid function was not important enough to be included. It can be concluded that there is a greater need for research into thyroid-disease screening in diabetic patients as research points toward a higher prevalence of thyroid diseases in patients with both type 1 and type 2 diabetes.
Key Takeaways
- Diabetes mellitus and thyroid diseases are very common endocrine disorders that are closely linked. It is extremely common for individuals to experience both conditions together.
- In 2019, diabetes directly caused 1.5 million deaths with 48% being before the individual reached 70 years old.
- Diabetes is classified into four major categories: Type 1, Type 2, Gestational, and other minor categories.
- Thyroid dysfunction (TD) affects around 6.6% of adults in Europe and the United States.
- 17% to 30% of adults with type 1 diabetes were also diagnosed with autoimmune thyroid disease (AITD).
- Mild, chronic TSH elevation, a major risk factor for thyroid cancer, is also seen in diabetic patients.
- It is hypothesized that thyroid-disease screening in diabetic patients will be beneficial for future diabetic patient care.
