Diabetes mellitus (DM) and thyroid diseases (TD) are common endocrine disorders in the general population. According to the year 2014 statistics, the International Diabetes Federation (IDF) has estimated that around 387 million people are living with diabetes worldwide. Several countries of the Eastern Mediterranean Region (EMR) are among the top ten countries with the highest prevalence in diabetes. The regional prevalence is ranging from 7% in Egypt to over 20% in some of the Gulf Cooperation Council (GCC) countries [
The prevalence of diabetes varies between different populations. In Oman, diabetes has emerged as a major and growing health problem. The first national diabetes survey was conducted in 1991 and showed that the prevalence of diabetes in adults aged 20 years and over was 8.3%. Subsequent surveys showed that the prevalence is increasing and it reached 12.3% in 2008 [
Thyroid diseases are also common in the general population. There is a great difference in the prevalence of the thyroid diseases in the general population, ranging from 6.6% to 13.4% [
The association between diabetes and thyroid disease is well known. The first studies were published in year 1997 [
The strong association between diabetes and thyroid diseases encouraged the American Diabetes Association (ADA) to propose that people with diabetes must be checked periodically for thyroid dysfunction [
Our aim in this study is to establish the association between diabetes mellitus and thyroid diseases in Omani population, to describe the morphology and the type of thyroid disease associated with diabetes mellitus, and to determine whether thyroid disease in diabetes mellitus is causatively associated with glycemic control. Based on the results of this study, the periodic screening for thyroid diseases in diabetics can be decided.
This is a retrospective cross-sectional study conducted at Sultan Qaboos University Hospital (SQUH) which is a tertiary teaching hospital, in Muscat region in the Sultanate of Oman. A random sample of 500 Omani type 2 diabetics who had attended the endocrinology and the family medicine outpatient clinics between July 2010 and July 2011 were selected for the study. Their medical record numbers were obtained by the help of the hospital information system (HIS). The final number of the diabetic patients who fulfilled the inclusion and exclusion criteria was found to be 285. A similar number of an independent control group was recruited for this study from SQU Health Center. The control groups were 288 nondiabetic healthy individuals, who had attended the abovementioned clinic for either minor medical problems or for routine medical checkup.
The inclusion criteria included were type 2 Omani diabetics of both sexes, whose age is equal or above 30 years and who were on antidiabetic treatment for at least one year. The exclusion criteria included non-Omani diabetic patients, type 1 diabetics, diabetics with unknown thyroid status, and newly diagnosed diabetics (duration < 1 year).
The confidentialityof patients was maintained during the research. Patient’s identifiers including names and hospital identification numbers were substituted by serial numbers. No new tests were carried out during the research.
Since the analysis of both groups is based on a preexisting data obtained from a previous research study, individual informed consent was not collected. However permission was obtained from the concerned department and the study was approved by the SQU ethical committee.
The following parameters were collected using chart review: age, sex, duration of diabetes mellitus, duration of thyroid disease, thyroid morphology (based on clinical examination notes and/or radiological imaging), thyroid function, thyroid antibodies, and mean glycated hemoglobin (HbA1C), from the readings of the last 4 years.
Thyroid dysfunction was classified as clinical hypothyroidism (C-Hypo) if TSH levels were greater than 5.6
Statistical analysis was done using Statistical Package for Social Sciences (SPSS 16). Mean ± SD was determined for quantitative data and frequency for categorical variables. Independent test was performed in all continuous variables. Normal distribution of the data was checked before any
285 diabetic patients with mean age of 57 (± 11.5) were examined, 93 males (32.6%) and 192 females (67.4%) in whom thyroid dysfunction was found in 36 patients (12.6%) (14% males and 86% females). Thyroid dysfunction was significantly higher in the female gender with
Baseline characteristics of study subjects with or without thyroid dysfunction among type 2 diabetic patients aged >30 years.
All samples |
Diabetic subjects without thyroid dysfunction |
Diabetic subjects with thyroid dysfunction |
|
|
---|---|---|---|---|
Age (years) |
57.05 ± 11.46 | 56.89 ± 11.36 | 58.14 ± 12.27 | 0.54 |
Gender | ||||
Male |
93 (32.6) | 88 (35.3) | 5 (13.9) | 0.01 |
Female |
192 (67.4) | 161 (64.7) | 31 (86.1) | |
Duration of diabetes (years) |
11.29 ± 7.94 | 11.42 ± 8.18 | 10.38 ± 5.97 | 0.98 |
HGBA1C |
7.99 ± 1.9 | 8.05 ± 1.9 | 7.55 ± 1.48 | 0.16 |
Type of treatment |
||||
Diet | 7 (2.5) | 5 (2.0) | 2 (5.6) | 0.28 |
OHA | 152 (54.3) | 132 (54.1) | 20 (55.6) | |
Insulin | 58 (20.8) | 48 (19.9) | 10 (27.8) | |
Insulin + OHA | 63 (22.3) | 59 (24.0) | 4 (11.1) | |
HGBA1C + | ||||
Controlled (<8) | 153 (57.5) | 133 (56.6) | 20 (64.5) | 0.40 |
Uncontrolled (> or = 8) | 113 (42.5) | 102 (43.4) | 11 (35.5) |
Out of the diabetic patients with abnormal thyroid function, 18 (6.3%) had overt hypothyroidism (16.7% males and 83.3% females), 13 females (4.6%) had overt hyperthyroidism, four females (1.4%) had subclinical hypothyroidism, and one female had subclinical hyperthyroidism (0.4%) (Figure
Distribution of thyroid dysfunction in Omani patients according to sex.
Distribution of thyroid dysfunction in the control group according to their mean age.
Thyroid morphology was found to be abnormal in 6 females of whom one had diffuse goiter (0.4%), one had multinodular goiter (0.4%), two had solitary nodule (0.7%), and two had thyroidectomy (0.7%). However, thyroid morphology was unknown in 156 (55.1%) patients (33.3% males and 66.7% females).
We also examined the association between thyroid dysfunction and diabetes control (defined by the mean HbA1c), in which we found that overt hypothyroidism was observed at a mean HbA1c of 7.6 (± 0.5), overt hyperthyroidism at a mean HbA1c of 7.4 (± 0.5), and subclinical hypothyroidism at a mean HbA1c of 7.8 (± 0.7) (Figure
Distribution of thyroid dysfunction in diabetic patients according to their diabetic control (represented by the mean glycated HGB).
288 nondiabetic patients were selected as a control group to compare the prevalence of thyroid dysfunction with the diabetic subjects. The mean age of the control subjects was 46 (± 8.4). This group includes 118 males (41%) and 170 females (59%). Thyroid dysfunction was found in 14 (4.9%) patients, 7 males (50%) and 7 females (50%). Out of those patients, one female had hypothyroidism, three had hyperthyroidism (two males and one female), seven had subclinical hypothyroidism (four males and three females), and three had subclinical hyperthyroidism (one male and two females) (Table
Baseline characteristics of the healthy nondiabetic control subjects.
Characteristic | Control subjects |
---|---|
Age |
46 ± 8.4 |
Gender | |
Males |
118 (41) |
Females |
170 (59) |
Thyroid dysfunction (%) | 4.9 |
Overt hypothyroidism | 1 |
Overt hyperthyroidism | 3 |
Subclinical hypothyroidism | 7 |
Subclinical hyperthyroidism |
3 |
Distribution of thyroid dysfunction between the diabetics and the healthy controls.
The mean age for thyroid dysfunction for this group was 40 years for overt hypothyroidism, 41 years for overt hyperthyroidism, 49 years for subclinical hypothyroidism, and 44 years for subclinical hyperthyroidism.
This study demonstrates a 12.5% prevalence of thyroid dysfunction (TD) in the diabetic patients studied, which is three times higher than the control group in which the prevalence was only 4.9% (Figure
Hypothyroidism was the most frequent thyroid dysfunction found (6.3%) corresponding to half of the percentage of TD among the study group which is 12.5% and accounts for more than sixfold the control group, while subclinical hypothyroidism was the most frequent thyroid dysfunction observed among the control group (2.4%) with equal distribution among sexes. Akbar et al. reported a similar result in their study of Saudi T2DM patients in 2006 [
In addition, a recent study done in Saudi Arabia reported a higher prevalence of thyroid dysfunction in Saudi type 2 diabetics reaching 28.5% of which 25.3% had hypothyroidism which was explained by the high prevalence of latent autoimmune diabetes of adults in the area reaching 26% [
It is reported that DM appears to influence thyroid function in at least two sites, one at the level of hypothalamic control of thyroid stimulating hormone (TSH) release and the other at the conversion of thyroxine (T4) to 3,5,3′-triiodothyronine (T3) in the peripheral tissues [
Perros et al. reported that “the thyroid hormones, triiodothyronine (T3) and tetraiodothyronine (T4) are insulin antagonists that also potentiate the action of insulin indirectly.” TRH synthesis decreases in diabetes, and this could be responsible for the occurrence of low thyroid hormone levels in diabetics [
In the literature, it is well known that thyroid hormones directly control insulin secretion, thus affecting the control of diabetes. In hypothyroidism, there is a reduction in glucose-induced insulin secretion by beta cells, and the response of beta cells to glucose or catecholamine is increased in hyperthyroidism due to increased beta cell mass. Moreover, insulin clearance is increased in thyrotoxicosis [
There is little consensus on thyroid disease screening strategies in routine diabetes care and whether a specific screening policy is at all necessary in diabetic patients. The recommendations from some guidelines are vague with a lot of variation ranging from ignoring the thyroid function test to yearly testing [
The prevalence of TD in T2DM is almost comparable to that in T1DM, although the genetic links are less clear [
Unfortunately, 156 (55.1%) of our diabetic patients had unknown thyroid morphology for which it was difficult to conclude its association with the antidiabetic treatment which was proved significant in the Turkish population [
In regard to the other factors examined, female gender was the only risk factor for developing thyroid dysfunction in our study, similar to the results in many other studies [
Some limitations in our study must be discussed. As our study is a retrospective cross-sectional study, the thyroid morphology was unknown in 55.1% of the sample group, for which we could not establish its association with diabetes. In addition, the thyroid gland imaging studies were not found in majority of the patients. For the same reason we were unable to study the effect of diabetes treatment on thyroid function and morphology. Other important confounders which could not be obtained were the family history of TD, smoking status, and the Body Mass Index (BMI) which were shown to be significant factors in the development of TD in other trials [
Thyroid dysfunction is common in type 2 diabetics compared to the general population in the Sultanate of Oman. This indicates that screening for thyroid function should be routinely performed. However, we suggest future observational studies to further explore the other risk factors for the development of thyroid dysfunction in diabetics. In addition, further studies are required on the cost effectiveness and frequency of screening for thyroid dysfunction in type 2 diabetic patients.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors would like to acknowledge the great assistance of the Department of Biochemistry at the Sultan Qaboos University (SQU) for helping with the sample used in the study. The authors also appreciate the great support of the Research and Statistics Department at the Oman Medical Specialty Board (OMSB).