Insulin and thyroid hormones play important roles in our body. Insulin helps
regulate the glucose level while the thyroid hormones affect various cells and
tissues, metabolizing protein, lipids, and glucose. Hyperthyroidism and
thyrotoxicosis are potential hazards for type 2 diabetes mellitus. There is a
high prevalence of hypothyroidism being more common compared to hyperthyroidism
coexisting with diabetes mellitus. Thyroid hormones affect glucose metabolism
through its action on peripheral tissues (gastrointestinal tract, liver,
skeletal muscles, adipose tissue, and pancreas). High-level thyroid hormone
causes hyperglycemia, upregulation of glucose transport, and reduction in
glycogen storage. The reverse is observed during low levels of thyroid hormone
along with insulin clearance. The net result of thyroid disorder is insulin
resistance. Type 2 diabetes mellitus can downsize the regulation of thyroid
stimulating hormones and impair the conversion of thyroxine to triiodothyronine
in peripheral tissues. Furthermore, poorly managed type 2 diabetes mellitus may
result in insulin resistance and hyperinsulinemia, contributing to the
proliferation of thyroid tissue and an increase in nodule formation and goiter
size. Although metformin proves advantageous for both type 2 diabetes mellitus
and thyroid disorder patients, other antidiabetics like sulfonylureas,
pioglitazone, and thiazolidinediones may have adverse effects on thyroid
disorders. Moreover, antithyroid drugs such as methimazole can weaken glycemic
control in individuals with diabetes. Thus, an interplay between both
endocrinopathies is observed and individualized care and management of the
disorder needs to be facilitated.