You probably know that having certain conditions increases your chances of developing type 2 diabetes, such as obesity, high blood pressure, and high cholesterol. But did you know that having a thyroid disorder may also raise your diabetes risk? Here’s what to know about how your thyroid hormones affect blood sugar and advice for managing thyroid problems to help prevent type 2 diabetes.

Research on Thyroid Hormone Levels and Diabetes

While researchers still haven’t clarified the exact connection between thyroid dysfunction and diabetes, there is enough evidence to conclude that they occur too frequently together for this to be considered a coincidence.

Epidemiologic studies across multiple ethnic groups estimate that up to 20% of people with type 2 diabetes also have hypothyroidism (underactive thyroid). This is a higher prevalence than in the general population, in which diabetes prevalence is just over 10%.

In a 2022 systematic review and meta-analysis published in the Journal of Clinical Endocrinology & Metabolism, a group of researchers combined the evidence from six earlier studies addressing the connection between thyroid function and type 2 diabetes risk.

Overall, their analysis found that having hypothyroidism increased the risk of being newly diagnosed with diabetes by 26%. However, they noted that the evidence is limited and more study is needed.

In particular, the researchers recommended more studies on the role of thyroid hormones in individuals with prediabetes, which is a precursor to type 2 diabetes. In one of the studies included in the meta-analysis, published in 2016 in BMC Medicine and including data from almost 8,500 adults in the Netherlands, people with prediabetes and low thyroid function were more than twice as likely to progress to full-blown type 2 diabetes compared to those with normal thyroid hormone levels. Even “low normal” thyroid functioning increased risk.

What about the opposite problem—too much thyroid hormone circulating in the body? Although the 2022 review and meta-analysis found some evidence that an overactive thyroid (hyperthyroidism) can affect the way the body makes and uses glucose and insulin, the relationship wasn’t statistically significant.

How Does Thyroid Hormone Affect Blood Sugar?

An imbalance in your thyroid hormones—either too high or too low—can affect the way that your liver makes and processes glucose (sugar). If the imbalance isn’t addressed, it can impair blood glucose management for people with diabetes.

Additionally, researchers have found that thyroid stimulating hormone (TSH) may directly affect the level of the hormone leptin, which influences how hungry you feel and therefore plays a role in managing your body weight. Thyroid hormones may also affect how sensitive the body is to insulin.

In multiple studies, even in people without a diagnosed thyroid dysfunction, higher levels of TSH (an indicator of overt hypothyroidism) were associated with higher blood sugar levels and more insulin resistance.

Aside from its effects on the body, low thyroid hormone can also play a role in how well a person is able to manage their diabetes. Hypothyroid Symptoms such as hunger, depression, and fatigue can make sticking to a healthy diet and getting enough physical activity difficult.

How Does Thyroid Hormone Affect Insulin?

In addition to affecting the way that the body makes and uses glucose, thyroid hormones also affect the way your body makes and uses insulin.

Studies in animals have shown that the fat cells (adipocytes) and skeletal muscle cells of rats with hypothyroidism are less responsive to insulin. This means that the cells are less able to use the glucose in the bloodstream. Researchers suspect that this leads to insulin resistance, a risk factor for type 2 diabetes, in humans as well.

Under regular conditions, the beta cells in the pancreas react to increased levels of glucose in the blood by releasing just enough insulin to bring blood sugar levels down to normal. In people with hypothyroidism, the beta cells secrete more insulin than usual. For people with diabetes who use insulin, uncontrolled hypothyroidism can lead to episodes of hypoglycemia.

Hypothyroidism also affects your metabolism and causes it to slow down. This means that any medications taken, including insulin, will stay in your system for longer than usual. People taking oral medications or injecting insulin to control their blood sugars might find that their blood glucose levels are lower than usual. They may experience hypoglycemic episodes, which can be dangerous if not treated.

Until your thyroid hormones are balanced with medication, your health care provider might need to reduce your dosage of insulin or oral medication to prevent you from experiencing hypoglycemia. Conversely, once your hypothyroidism is appropriately treated, your provider may need to adjust the previously decreased doses.

Manage Your Thyroid Health to Prevent Diabetes

Thyroid dysfunction is associated with changes in your food intake, metabolism, body weight, and body temperature. These changes can lead to metabolic syndrome, which raises the risk for type 2 diabetes.

Managing your thyroid appropriately can help you decrease your risk factors for diabetes, but there isn’t enough evidence to say that this can prevent diabetes completely. If you do develop diabetes or you already have the condition, balancing your thyroid hormones can help you manage both conditions better.

Hypothyroidism is mainly treated with a medication called levothyroxine. This is a pill taken by mouth once a day, ideally on an empty stomach.

The exact dose you need will be unique to your body. Your health care provider will monitor your lab work and adjust your dosage of medication as needed. You’ll likely need to have your labs drawn every four to eight weeks until your thyroid hormones reach their target levels.

Your health care provider will also want to monitor your other health conditions, such as heart disease. Overtreating low thyroid hormones can result in angina (chest pain) and atrial fibrillation.

Once you reach the right dose of levothyroxine, lab work to monitor your levels can be done every six months if your condition is stable. Some providers will even extend this to yearly as long as you aren’t showing any signs of hypothyroidism.

The effectiveness of your medication dose will be determined by your TSH levels and your signs and symptoms. Most people have a good prognosis with treatment, and symptoms usually reverse in a few weeks or months.

When to Contact a Doctor

When high blood sugar is left untreated, it can lead to serious complications. These include damage to your eyes, kidneys, nerves, heart, and blood vessels. So it’s important to prevent or effectively manage your glucose levels if you have diabetes or prediabetes.

Both hypothyroidism and diabetes are relatively easy to detect with simple blood tests. Once diagnosed, both conditions have well-researched standard treatments.

Common symptoms of diabetes include:

• Frequent urination
• Increased thirst
• Lethargy
• Unintended weight loss
• Common signs of low thyroid hormones include:
• Constipation
• Depression
• Fatigue
• Intolerance to cold
• Lethargy
• Low blood pressure (hypotension)
• Slow pulse
• Weight gain

If you suspect you have signs of diabetes or thyroid dysfunction, contact your health care provider.