105
levels of fasting and postprandial insulin and pro-insulin leading to hyperinsulinemia, marked rise in free fatty acid concentrations. The enhanced transport and
utilisation of peripheral glucose with massive increase in glucose metabolism
results in non-oxidative metabolism and increased production of lactates in body.
These lactates then undergo Cori cycle (lactic acid cycle) in liver and converted to
glucose. However, the increased peripheral uptake is not governed by insulin in
hyperthyroid patients (insulin resistance). Moreover, it has been observed that thyrotoxicosis results in apoptosis of insulin producing pancreatic β cells. It is the main
pathology involved in poor glycaemic control in diabetic patients with concomitant
hyperthyroidism (Fig. 6.3) [19, 20].
Hypothyroidism and Diabetes
Clinical impact of hypothyroidism in diabetic patients is less obvious as compared
to hyperthyroidism. Decreased levels of thyroid hormones result in decreased intestinal absorption, decreased hepatic output and decreased peripheral glucose utilisation. The glycemic control is less difficult in diabetic patients with hypothyroidism
owing to reduced hepatic glucose output, a compensation for insulin resistance in
these patients (Fig. 6.3) [19, 20].
Effects of Diabetes on Thyroid Function
Poor glycaemic control in diabetic patients leads to impaired thyroid function. In
diabetic individuals, the conversion of T3 to T4 is impaired resulting in low T3 state,
which can be reversed with glycemic control in type II diabetes. The nocturnal levels of TSH decrease in diabetes along with reduced TSH response to TRH. Elevation
of circulating insulin as a consequence of insulin resistance in diabetic patients
causes thyroid enlargement and development of thyroid nodules [18, 20].
Thyroid Hormones and Lipids
Role of Thyroid Hormones in Cholesterol Biosynthesis
Lipids and cholesterols are transported across the blood with the help of lipids and
protein complexes, commonly known as lipoproteins. These lipoproteins include
low-density lipoproteins (LDL), very low-density lipoproteins (VLDL), and highdensity lipoproteins (HDL). A transcription factor named as, sterol regulatory element binding protein (SREBP) 1and 2, regulates the expression of serum LDL
receptors. The primary function of LDL receptors is to regulate blood cholesterol
levels [22]. Circulating blood cholesterol is transported back to liver in a process
named as reverse cholesterol transport. The enzyme hepatic lipase breaks down
6 Impaired Thyroid Function in Metabolic Disorders
levels of fasting and postprandial insulin and pro-insulin leading to hyperinsulinemia, marked rise in free fatty acid concentrations. The enhanced transport and
utilisation of peripheral glucose with massive increase in glucose metabolism
results in non-oxidative metabolism and increased production of lactates in body.
These lactates then undergo Cori cycle (lactic acid cycle) in liver and converted to
glucose. However, the increased peripheral uptake is not governed by insulin in
hyperthyroid patients (insulin resistance). Moreover, it has been observed that thyrotoxicosis results in apoptosis of insulin producing pancreatic β cells. It is the main
pathology involved in poor glycaemic control in diabetic patients with concomitant
hyperthyroidism (Fig. 6.3) [19, 20].
Hypothyroidism and Diabetes
Clinical impact of hypothyroidism in diabetic patients is less obvious as compared
to hyperthyroidism. Decreased levels of thyroid hormones result in decreased intestinal absorption, decreased hepatic output and decreased peripheral glucose utilisation. The glycemic control is less difficult in diabetic patients with hypothyroidism
owing to reduced hepatic glucose output, a compensation for insulin resistance in
these patients (Fig. 6.3) [19, 20].
Effects of Diabetes on Thyroid Function
Poor glycaemic control in diabetic patients leads to impaired thyroid function. In
diabetic individuals, the conversion of T3 to T4 is impaired resulting in low T3 state,
which can be reversed with glycemic control in type II diabetes. The nocturnal levels of TSH decrease in diabetes along with reduced TSH response to TRH. Elevation
of circulating insulin as a consequence of insulin resistance in diabetic patients
causes thyroid enlargement and development of thyroid nodules [18, 20].
Thyroid Hormones and Lipids
Role of Thyroid Hormones in Cholesterol Biosynthesis
Lipids and cholesterols are transported across the blood with the help of lipids and
protein complexes, commonly known as lipoproteins. These lipoproteins include
low-density lipoproteins (LDL), very low-density lipoproteins (VLDL), and highdensity lipoproteins (HDL). A transcription factor named as, sterol regulatory element binding protein (SREBP) 1and 2, regulates the expression of serum LDL
receptors. The primary function of LDL receptors is to regulate blood cholesterol
levels [22]. Circulating blood cholesterol is transported back to liver in a process
named as reverse cholesterol transport. The enzyme hepatic lipase breaks down
6 Impaired Thyroid Function in Metabolic Disorders