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Cardio Diabetes Medicine 2017 141

Thyroid Dysfunction, Diabetes

and the Cardiac Link

Dr. Muthukumaran Jayapaul, MBBS., MD (UK)., MRCP (UK)., CCT (Int. Med & Endo).,
Arka Center for Hormonal Health Pvt Ltd

Abstract Thyroid dysfunction, Diabetes and the
Thyroid dysfunction and Diabetes mellitus are two Cardiac link
common disorders encountered in day-to-day endo- Thyroid dysfunction and Diabetes mellitus are two
crine practice. The prevalence of both conditions re- common disorders encountered in day-to-day endo-
mains high and continues to rise as with advancing crine practice. The prevalence of both conditions re-
age. Hypothyroidism and hyperthyroidism has been mains high and continue to rise as with advancing age.
investigated to be associated with diabetes mellitus. Hypothyroidism and thyroid over-activity has been
Common susceptibility genes have been acknowl- investigated to be associated with diabetes mellitus.
edged to confer a risk for development of both au- A recent meta-analysis reported an increased prev-
toimmune thyroid disease and type 1 diabetes mel- alence of around 11 % of thyroid dysfunction in pa-
litus. The association between autoimmune thyroid tients with diabetes[1]. The major etiological factor of
disease and type 1 diabetes has been recognized as concern in these patients is suspected autoimmunity.
a variant of autoimmune polyglandular syndrome Most parts of the world including India have become
referred to as APS3 variant.In hypothyroidism, glu- iodine replete, post-iodisation programmes in their
cose-induced insulin secretion by the β-cells is re- respective countries except for isolated areas. The
duced. The rates of glucose oxidation and glycogen current common etiological factors stand as primary
synthesis are also decreased in hypothyroidism. Ex- atrophic hypothyroidism, Hashimoto’s thyroiditis and
cess thyroid hormone leads to hyperglycaemia via autoimmune hyperthyroidism. The knowledge of this
multiple mechanisms which association is crucial so that appropriate diagnostic

include increased glucose absorption in the gastro- and therapeutic provisions could be made to prevent
intestinal tract, increased hepatic glucose output, hy- worsening of both these conditions. When untreated
perinsulinaemia, increased free fatty acid levels and both hypothyroidism and diabetes aggravate compli-
increased peripheral glucose transport. The increased cations such as increasing cardiovascular morbidity
hepatic glucose output leads to hyperinsulinaemia, and mortality, worsening of lipids, fluctuating glycae-
progression to glucose intolerance and further de- mia, and declining cognitive function.
velopment of peripheral insulin resistance.Hyperthy- Untreated or sub-optimally managed diabetes both
roidism may complicate or exacerbate pre-existing type1 and type 2 diabetes, may induce a low T3 state
heart disease because of increased myocardial ox- characterized by both low total and free T3 levels but
ygen demand, increased contractility and heart rate. normal TSH and free T4 levels. It is well documented
The prevalence of atrial fibrillation peaks up to 15 % that both thyroid diseases and type 1 diabetes share
in patients older than 70 years. There is evolving ev- a common etiological factor – autoimmunity. In type
idence that early management of sub-clinical hypo- 2 diabetes the core pathological defect is likely to
thyroidism and sub-clinical hyperthyroidism may play be due to inappropriate secretion of insulin – beta
a role, in preventing or worsening heart disease in cell dysfunction. Here the pancreas is unable to com-
individuals less than 65 years. The knowledge of this pensate for the prevailing insulin resistance. This de-
association is crucial so that appropriate diagnostic fective insulin secretion leads to various metabolic
and therapeutic provisions could be made to prevent aberrations in Type 2 diabetes, including decreased
worsening cardiovascular risk.

Cardio Diabetes Medicine