Thyroid Disorders Can Contribute To The Development of Type 2 Diabetes

A large cohort study investigated the association between thyroid disorders and type 2 diabetes.

Type 2 diabetes is due to insulin resistance accompanied with insulin deficiency resulting in hyperglycemia. If left untreated, hyperglycemia can cause several acute and chronic complications affecting the eyes, heart, and kidneys, and even lead to death. Thyroid hormones are essential for carbohydrate metabolism, thus, thyroid dysfunctions may influence the development of diabetes mellitus. This is a nation-wide cohort study that investigated the effects of thyroid disorders on the occurrence of type 2 diabetes.

The study included patients 18 years and older who were recently diagnosed with thyroid diseases, who were then further divided into two subgroups: the hyperthyroidism subgroup (14,903 patients) and the hypothyroidism subgroup (4131 patients). Patients who had a history of diabetes were excluded. The control group included a total of 72,896 participants who have never been diagnosed with any thyroid disorders and/or diabetes. The outcome of this study was the diagnosis of type 2 diabetes and the end of the study was defined by occurrence of event. The participants were then followed for 10 years. P values less than 0.005 were considered to be statistically significant.

The researchers observed that the incidence of type 2 diabetes was higher in the thyroid disease group than in the control group (HR 1.23, 95% CI 1.16-1.31). Female patients showed a significantly higher incidence of type 2 diabetes in the thyroid disease group than the control group (HR 1.27, 95% CI 1.18-1.37). That might be due to the small number of males included in the study, or because males are less commonly seen with thyroid disorders. Furthermore, patients younger than 65 years showed a higher incidence of type 2 diabetes.

This study, however, had some limitations. Type 2 diabetes is a very common disease and may be related to many factors such as age, genetics, family history and others. Some factors were very hard to rule out and that might have affected the reliability of the results. In addition to that, the quality of the study may introduce some bias. Moreover, hypothyroidism, unlike hyperthyroidism, can be very hard to diagnose and the signs and symptoms may go unnoticed by patients and even endocrine specialists.

In conclusion, the 10-year results suggest that both hyperthyroidism and hypothyroidism had higher cumulative rates of type 2 diabetes occurrence than the control group. Thyroid disorders could contribute to the development of type 2 diabetes. Physicians should encourage patients with thyroid diseases to check blood sugar levels regularly.

Practice Pearls:

• This is a nationwide cohort study aimed to evaluate the impact of thyroid disorders on the incidence of type 2 diabetes. The study included a total of 19,034 patients with thyroid disorders and 72,896 participants in the control group. The length of the study was 10 years.
• The incidence of diabetes was higher in the thyroid disease group than in the control group. Female participants and those who were younger than 65 years old had a higher risk of developing type 2 diabetes.
• Some limitations of the study were the low quality of the study, higher risk of bias and inability to rule out all factors that may cause diabetes.

Chen RH, et al. Thyroid diseases increased the risk of type 2 diabetes mellitus. Medicine. 2019 May; 98 (20).

Nadeen Ayad, BCPS, PharmD Candidate, Skaggs School of Pharmacy, University of Colorado