Thyroid disorders are common conditions in the general US population affecting close to 27 million people. It is an extreme condition affecting the endocrine system that helps in regulating reproduction, growth, and nutrient use. However, thyroid dysfunction has been widely reported among patients with diabetes across the world due to both being a hormonal problem. Type 2 diabetes mellitus has an underlying pathology with thyroid dysfunction as the two conditions share several genes. The conditions co-occur and are inherited, whose mutations increase the risk of developing either diabetes, thyroid disease, or both ( Ogbonna & Ezani, 2019) . This means a diabetic patient is an increased risk of developing thyroid disorder and vice versa. This literature review examines the relationship that exists between type 2 diabetes mellitus and related thyroid infections in the female. It also defines the prevalence of thyroid disease in diabetic patients and the likelihood of a patient with hyperthyroidism to develop diabetes.
Thyroid dysfunctions are disorders of the thyroid gland manifesting as hyperthyroidism and hypothyroidism based on the levels of thyroid-stimulating hormone. The thyroid gland is found in the lower neck of a person with the role of regulating body metabolism by releasing thyroid hormones ( Liu et al., 2018) . Hyperthyroidism is when the thyroid gland releases too much hormone that increases metabolism. It is an increase in the functioning of the thyroid gland that increases the thyroid hormone. The most common thyroid dysfunction in patients with diabetes mellitus is subclinical hypothyroidism.
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On the other hand, hypothyroidism occurs when the thyroid gland releases too little hormone that slows down the body functions. Hypothyroidism refers to a decreased functioning of the thyroid gland inpatient, which leads to a subclinical condition or a state of myxedema. The thyroid hormones in a person help the body to metabolize carbohydrates and facilitate the proper functioning of the pancreas. This means a lower thyroid hormone causes a drop in insulin levels that can increase the risk of high blood sugar level ( Liu et al., 2018).
The role of hyperthyroidism in type 2 diabetes mellitus was first investigated in 1927 with findings that thyroid disorders worsen the risk of diabetes. The first study stated that surgically removing parts of the thyroid gland can help in treating diabetes, as it can restore glucose tolerance in diabetic patients with hyperthyroid ( Ogbonna & Ezani, 2019) .. Type 2 diabetes mellitus has been shown to have an intersecting underlying pathology with hypothyroidism. A literature review has documented how the two conditions relate to and influence each other because of having underlying pathological influence. Previous studies have shown that thyroid dysfunction is joint in patients with type 2 diabetes mellitus than any other person ( Tsatsoulis, 2018) . When thyroid disease develops in a diabetic person, they will struggle to control blood glucose.
Risk factors of Thyroid Dysfunction and Diabetes Mellitus
Several studies have confirmed and documented a deep underlying relationship between thyroid dysfunction and type 2 diabetes. The studies have cited several intertwining biochemical, genetic, and hormonal functions as risk factors to the association ( Wang, 2013) . Biochemically subclinical hypothyroidism is one of the most common disorders associated with type 2 diabetes mellitus. Several risk factors have been associated with thyroid dysfunction in type 2 diabetes mellitus. The most common risk factors that associate thyroid dysfunction with diabetes are gender and comorbidities. These risk factors apply to both cases of diabetes and thyroid disorders ( Ogbonna & Ezani, 2019) .
Neonates and the elderly are the most at-risk people for thyroid disorder and therefore tend to develop type 2 diabetes mellitus. Older patients with thyroid dysfunctions are more prone to developing diabetes due to insulin resistance and abnormalities of insulin secretion that are caused by age ( Heidari, Abdani & Mansournia, 2018) . The influence of thyroid disorders on carbohydrate metabolism becomes relatively weak in older patients. Other at-risk population includes women and individuals who had type 1 diabetes for a long time. For example, studies have pointed out that female patients with hyperthyroidism are more prone to developing diabetes mellitus than male patients.
At the same time, interfering with carbohydrates metabolism in the body has been associated with promoting the development of diabetes mellitus. This is facilitated through insulin resistance and abnormal secretion of insulin in the body. According to Heidari, Abdani & Mansournia (2018), Individuals with low thyroid hormone levels have an increased risk of diabetes. This is because thyroid hormones are needed for body metabolism and energy expenditure, which means low hormone levels are a risk factor for diabetes.
Low thyroid hormones in the body cause a drop in insulin levels, which affects the absorption of blood sugar. This increases the rate of diabetes in an individual since low insulin levels cause high blood sugar and trigger diabetes. Other connections between type 2 diabetes mellitus and thyroid disorder are the fact that they are both caused by an autoimmune process ( Tsatsoulis, 2018) . This means a patient with an autoimmune condition such as diabetes has a higher risk of developing another autoimmune disease such as thyroid disorder.
Epidemiology of Thyroid dysfunction and diabetes mellitus
Thyroid dysfunction is an endocrine disorder caused by an elevated thyroid-stimulating hormone. A survey conducted on the prevalence of thyroid disorder shows that hypothyroidism and hyperthyroidism are common types of thyroid disorder in patients with the condition. Hypothyroidism is the most common disorder in the adult population, and especially among older women, who also have high tendencies of developing diabetes.
About four million people in the United States are diagnosed with thyroid disorder affecting primarily young adults. Reports have shown that 6 percent of people have some form of a thyroid disorder, with the prevalence of thyroid disorder increasing to over 10 percent in people with diabetes. The prevalence of this condition increases with age, with older individuals experiencing higher cases of diabetes and thyroid disorder. Tsatsoulis (2018) also stated that thyroid disorder prevalence advances with age, in the sense that older people are likely to experience the disease compared to younger individuals.
Furthermore, the frequency of thyroid dysfunction is mostly seen in women than men, with 20 percent of all cases reported in women compared to only 4 percent in men. This means thyroid disorder in the diabetic population is higher in female patients than men. At the same time, there is a high incidence of thyroid disorders in young women with diabetes.
According to Tsatsoulis (2018), people with diabetes have an increased risk of developing a thyroid disorder. One in ten people with type 2 diabetes mellitus will have a thyroid condition, which shows the extent to which the two terms relate to each other. Diabetes has many genetic and environmental triggers associated with autoimmune diseases. It has numerous symptom and co-occurring conditions as thyroid dysfunctions that increases the risk of this association. Although type 2 diabetes mellitus is not an autoimmune disorder, studies have shown a higher occurrence of thyroid disorders such as hypothyroidism among diabetic patients ( Tsatsoulis, 2018) .
Furthermore, Pihlajamäki et al (2009) revealed a high prevalence of thyroid disorders in patients with diabetes mellitus. They have documented a higher than average incidence of thyroid dysfunction in patients with diabetes than in the healthy population. The prevalence of thyroid disease in diabetes is estimated at 10 percent of patients, where a majority of cases occur as hypothyroidism or hyperthyroidism. At the same time, the rate of postpartum thyroiditis is also higher in diabetic patients than ordinary people when diagnosed in women. Reports have indicated three times higher than the average prevalence of thyroid disorders in patients with type 2 diabetes mellitus.
This literature review has proven that there is a relationship between thyroid infection and diabetes mellitus. According to Wang (2013), there is a relatively high risk of diabetes development in patients with thyroid dysfunctions, especially in the short period after the presentation of thyroid disorder symptoms. In the same way, hyperthyroidism is associated with increasing the levels of thyroid hormone in the body, which may increase blood sugar level and development of diabetes.
Influence of Insulin Resistance
Insulin resistance is one of the vital facet connecting diabetes and thyroid dysfunction in patients. This is a condition that is associated with both hypothyroidism and hyperthyroidism and reported to cause impaired glucose metabolism in diabetic patients. Type 2 diabetes is characterized by insulin resistance since maintaining an intact insulin response helps a body to maintain healthy levels of blood glucose. This literature review has proven that there is a relationship between thyroid infection and diabetes mellitus ( Wang, 2013) . It shown that there is a relatively high risk of diabetes development in patients with thyroid dysfunctions, especially in the short period after the presentation of thyroid disorder symptoms. In the same way, hyperthyroidism is associated with increasing the levels of thyroid hormone in the body, which may increase blood sugar level and development of diabetes.
Pihlajamäki et al (2009) stated that insulin resistance in diabetic patients may increase thyroid gland nodularity. The insulin resistance is associated with subclinical hypothyroidism, which impairs the lipid balance while subjecting a patient to developing metabolic syndrome. Arduc et al., (2014) evidenced the association between subclinical hypothyroidism and diabetes mellitus. Clinical and subclinical hypothyroidism are both connected to insulin resistance. This is a state in the body of a person where cells are not responding to the insulin’s signal to take sugar out of the blood. Insulin resistance increases the blood sugar level in the body that triggers diabetes mellitus. Studies have also shown that insulin resistance in subclinical hypothyroidism leads to insulin secretion stimulated by high increase levels ( Arduc et al., 2014) .
Other preclinical studies have documented how insulin resistance causes hypothyroidism, such that peripheral muscles become less responsive in the hypothyroid condition. The link between hyperthyroidism and insulin resistance is shown with high glucose turnover or intestinal glucose absorption ( Heidari, Abdani & Mansournia, 2018) . When the body is unable to absorb the blood sugar levels from the blood, then there is a higher likelihood of developing diabetes. In this regard, patients with thyroid infection tend to be more vulnerable to diabetes.
At the same time, the high blood sugar level has been associated with an increased risk of kidney damage for a patient with thyroid dysfunctions ( Ogbonna & Ezani, 2019) . When a body develops insulin resistance, the chances are that the thyroid gland will develop more nodules and increases in size. This can lead to the development of other chronic diseases such as kidney disease or a coronary heart condition ( Zheng et al., 2019) . Hypothyroidism is often associated with reduced absorption of glucose from the gastrointestinal tract, which leads to prolonged accumulation of glucose in the peripheral. The condition causes metabolic abnormalities and clinical symptoms in the patient, which may affect blood sugar levels. Thyroid conditions interfere with metabolism and can interfere with a person’s blood sugar if they have diabetes. Some studies have noted that patients with diabetes and thyroid dysfunction have higher levels of hemoglobin, which indicates worse control of the diabetes mellitus condition Pihlajamäki et al (2009) .
Relationship between Diabetes Mellitus on Thyroid Diseases
Studies have shown that diabetes can lead to thyroid conditions by altering thyroid hormone levels. In some cases, insulin can imitate the actions of thyroid hormones by blocking the thyroid gland from producing hormones or increasing the thyroid hormone levels. Patients with diabetes mellitus have a higher risk of developing thyroid diseases due to the conditions closely relating to each other. Liu et al., (2018) wrote on this association and its implications on diagnosis and treatment. The study showed that patients who are diagnosed with type 2 diabetes mellitus will also have symptoms of thyroid diseases.
On the other hand, thyroid disorders have been shown to cause diabetes in patients. Individuals with thyroid disease have a higher risk of developing type 2 diabetes mellitus and experiencing symptoms of the condition. Diabetic patients who experience hyperthyroidism may experience an increase in the blood glucose level. Studies have shown that hyperthyroidism causes insulin to be processed or eliminated from the body quickly, leading to higher blood sugar levels and triggering diabetes mellitus ( Liu et al., 2018) . The thyroid hormone is involved in controlling insulin secretion in the body as well as glucose homeostasis. This makes it a crucial factor in the development of diabetes mellitus in patients with a thyroid disorder. Similarly, a slow metabolism due to hypothyroidism for diabetic patients may drop the blood glucose level
Diabetic patients are often associated with symptoms of thyroid dysfunction, which can be shown with several metabolic disturbances. Scientists have conducted cross-sectional studies that have shown a higher epidemic of thyroid disorders in patients with diabetic Mellitus. According to O gbonna et al., (2019), diabetic patients with poor glycemic control are described to have altered thyroid hormones that influence the development of diabetes. The presence of thyroid dysfunction in patients has also been shown to affect diabetes control. This is because hyperthyroidism worsens glycemic control and increases insulin requirements. Liu et al., (2018) discussed that hyperthyroidism affects glycemic control in the body, which can worsen diabetes with other conditions such as coronary heart disease. There is a possible deterioration in glycemic control for diabetic patients with hyperthyroidism, which requires lowering the glucose level. Thyroid hormones regulate carbohydrate metabolism, which means the dysfunction may lead to hyperglycemia. O gbonna et al., (2019) stated that hyperthyroidism promotes hyperglycemia inpatient, which is a recipe for the development of diabetes.
There is a complex interdependent interaction between thyroid dysfunction and diabetes mellitus, whereby patients with thyroid diseases have a higher risk of developing diabetes mellitus and vice versa. Both diabetes and thyroid disease are endocrine and hormone problems, which makes them related to each other. The studies have pointed out that these conditions coexist in patients because they involve a dysfunction of the endocrine system ( Ogbonna & Ezani, 2019) . Patients with diabetes mellitus have a higher risk of experiencing symptoms of thyroid disease. This is because the conditions are endocrine caused by an elevated thyroid-stimulating hormone.
This literature review provides essential clinical information that can help in designing treatment options thyroid dysfunction and diabetes mellitus conditions. Studies have shown existence of a deep link between these two conditions based on the metabolic relationships in the body. This literature review has proven that there is a relationship between thyroid infection and diabetes mellitus, with a high prevalence that patients with thyroid disorder will develop type 2 diabetes, especially in the short period after the presentation of thyroid disorder symptoms ( Ogbonna & Ezani, 2019) . In the same way, hyperthyroidism is associated with increasing the levels of thyroid hormone in the body, which may increase blood sugar level and development of diabetes.
References
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Chen, R. H., Chen, H. Y., Man, K. M., Chen, S. J., Chen, W., Liu, P. L., ... & Chen, W. C. (2019). Thyroid diseases increased the risk of type 2 diabetes mellitus: A nation-wide cohort study. Medicine , 98 (20). Retrieved September 20, 2019, from https://www.ncbi.nlm.nih.gov/pubmed/31096476
Heidari, Z., Abdani, M., & Mansournia, M. A. (2018). Insulin resistance associated with differentiated thyroid carcinoma: penalized conditional logistic regression analysis of a matched case-control study data. International journal of endocrinology and metabolism , 16 (1). Retrieved September 19, 2019, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5903382/
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