Research Questions Link Between Thyroid Disorders and Type 2 Diabetes

In developed nations, without cases of iodine deficiency, the prevalence of thyroid disorders is almost as common as type 2 diabetes, with lots of overlapping in the cases of both diseases. In iodine-replete nations, autoimmunity is the primary cause of thyroid disorders(1). It is not uncommon for thyroid disease to co-exist with other autoimmune diseases like diabetes. In fact, the data shows several autoimmune ailments are on the rise in many countries. So, is there a connection between the two?

Type 1 diabetes (T1D) has a strong relation to genetics and autoimmunity, and a person suffering from it is at higher risk of developing thyroid disorders. But question regarding the risk of thyroid disorder in type 2 diabetes (T2D) has remained unanswered. T2D is much more common than T1D, accounting for more than 90% of cases of diabetes. T2D has been called the disease of lifestyle, often associated with familial history, obesity, and little to no exercise. But its relationship to autoimmunity is unclear.

Recently, results of a large-scale study with a follow-up period of 11 years from Tehran were published to see if there was a direct relationship between the two.

While it did not show any association between T2D and thyroid issues, although the study did demonstrate that elevated levels of thyroid peroxidase antibody (TPOAb) and thyrotropin (TSH) were independent predictors(2) of developing thyroid disease.

But, what are thyroid disorders?

The thyroid gland produces thyroid hormones, which play an essential role in the maintenance of metabolism, energy levels, mood, as well as sexual health. Thyroid diseases either lead to increased levels of thyroid hormones(hyperthyroidism) or decreased (hypothyroidism). Fall in levels of thyroid hormones is comparatively more common, accounting for more than 80% of cases in the developed nations. Causes of thyroid diseases are not understood fully. In developing countries, or commonly known as third world countries, iodine deficiency was the primary cause of hypothyroidism. But after the introduction of iodized salts and other dietary measures, iodine deficiency has become rare.

Nowadays, autoimmunity is the leading cause of thyroid disease.

Because of its relation to autoimmunity, it is commonly found in those suffering from T1D, lupus, rheumatoid arthritis, vitiligo, celiac disease and other autoimmune ailments (3). Some dietary habits may also trigger the disease, but still little is understood about it. In fact, in developed nations, some studies have shown the relation between thyroid autoimmunity and higher iodine intake(4). Gender also seems to be a factor, as thyroid disorders are also more common in females as compared to men.