Introduction
Prior studies have reported that thyroid dysfunction such as overt hypothyroidism and hyperthyroidism are associated with weight gain and loss. In Indian normal healthy adults, relationship between thyroid hormones and Body Mass Index (BMI) has previously been studied but not explained very well.
Aim
The present study aims to investigate the relationship between thyroid hormones and obesity measured by BMI in normal healthy adults who further classified in three categories as per the BMI in normal, overweight and obese.
Materials and Methods
This observational cross-divtional study was conducted between 1st May 2019 and 30th June 2019. Condivutively, adults who attended Out-Patient Department (OPD) of Department of Medicine at Hamidia Hospital as attendant of patients and healthy hospital’s staff were selected for the study. Thyroid-Stimulating Hormone (TSH), total Thyroxine (T4), total Triiodothyronine (T3), total cholesterol, Low-Density Lipoprotein Cholesterol (LDL-C), High-Density Lipoprotein Cholesterol (HDL-C), triglyceride and glucose levels were measured in all study subjects. Height, weight, Waist Circumference (WC) and Hip Circumference (HC) were measured and BMI and Waist to Hip Ratio (WHR) were calculated by formula. According to Asian guidelines for BMI, all subjects were divided into three groups as healthy normal (18.5-22.9 Kg/m2), Overweight (23-24.9 Kg/m2) and Obese (≥25 Kg/m2).
Results
Out of 100 study subjects, 58% were females and 42% were males. According to BMI, 33 (33%) participants were found in normal weight, 36 (36%) were in overweight and 31 (31%) were in obese group. Atherogenic lipid levels such as total cholesterol, LDL-C and triglyceride and blood glucose were found increased and HDL-C levels were found decreased in overweight and obese group. The TSH levels were found significantly increased in overweight and obese subjects as compared to normal subjects, also a statistically significant difference was found for TSH between overweight and obese subjects. Out of 100 subjects, 88% were shown euthyroidism, 10% were shown hypothyroidism and 2% were shown hyperthyroidism. Pearson’s correlation between BMI and TSH was not found significant in normal, overweight and obese groups, while a significant difference was noted between T3, T4 and BMI in overweight group.
Conclusion
In the present study, total 12% thyroid dysfunction was observed. In view of the relationship between BMI and thyroid hormones, any significant relationship was not found in Indian normal as well as obese adults groups.
Introduction
Obesity is a major growing health concern in India due to its increasing prevalence found in younger as well as adult populations [1]. Genetic susceptibility, lack of exercises or Increased food intake are few causes for obesity [2] which makes this population more vulnerable to various diseases such as Diabetes Mellitus (DM), Hypertension (HTN), Ischemic Heart Disease (IHD) and Chronic Kidney Disease (CKD) [3]. Thyroid dysfunction is one of the most common endocrine disorders worldwide. In India, 42 million peoples are suffering from various thyroid disorders [4]. Obesity and thyroid dysfunction are two common clinical conditions which have been linked together very closely [5]. Thyroid hormones regulate the metabolic rate of the body and thermogenesis. It is also suggested that thyroid hormones are involved in the regulation of appetite [6,7]. Thyroid dysfunction is allied with fluctuations in body weight and composition [8]. One of the study has revealed certain correlation with body weight and levels of thyroid hormones [9]. However, studies on thyroid dysfunction in obese adults are inconsistent [10,11]. The effect of obesity on thyroid dysfunction such as hypothyroidism has been studied in several epidemiological studies in Western countries [12-14]. Few studies found that obesity could increase risk of hypothyroidism [12,15,16]. On the contrary, other studies reported no increased risk of hypothyroidism among obese patients [13,14]. Hypothyroidism is related with reduced thermogenesis, low metabolic rate and is also correlated with higher BMI and greater frequency of obesity [17]. In Indian context, there is still lack of a definite conclusion on the association of obesity with thyroid dysfunction and studies from Asian Indians are still lacking.
Obesity can be defined by use of different anthropometric indices parameters such as height, weight, HC, WC, WHR and BMI. In many epidemiologic studies, BMI is used as a good measurement of obesity [18,19]. Furthermore, few anthropometric indices were established lately, such as a new Hip Index (HI) and A Body Shape Index (ABSI), and these methods showed to be corresponding to BMI [20,21]. As per WHO data on percentage body fat and morbidity, the normal reference limits for Asian Indians were found to be lower and even narrower when compared to white Caucasians [22]. In this consensus statement, guidelines for obesity and overweight based on BMI for Asian Indians were revised based on consensus developed by a Prevention and Management of Obesity and Metabolic Syndrome group [23]. According to this revised guidelines, Asian Indians are categorised as overweight (BMI 23.0-24.9 kg/m2) [8] and obesity (BMI ≥25 kg/m2) [23]. Therefore, in this study, author included Asian guideline for BMI other than previous studies to make the results more comprehensive in Asian populations. In the present study, authors determined the relationship between thyroid function as assessed by measurement of serum level of total T3, T4 and TSH hormones and BMI in Indian healthy adults.
Materials and Methods
This is an observational cross-sectional study carried out in the Department of Medical Biochemistry in collaboration with Department of Medicine, Gandhi Medical College associated with Hamidia Hospital, Bhopal, India from 1st May 2019 to 30th June 2019. Total 100 apparently normal healthy volunteers who were attending the Hamidia Hospital as attendant of patient and healthy hospital’s staff, normotensive, normoglyemic and age between 20 to 60 years were included in this study. Sample size was 100, because it was a hospital-based study as a part of an ICMR short-term studentship project for the 2 months duration. So, as per the Institutional Ethical Committee permission, only 100 healthy study subjects were recruited for this study. The subjects having diabetes mellitus, hypertension, history of metabolic syndrome, renal disease and thyroid disorders were excluded from the study.
All study participants were subjected to detailed history, general physical examination such as height, weight, BMI (as weight in kilogram, height in meter2), WC, HC and WHR and findings were recorded in case proforma sheet. All enrolled healthy adults were divided into three groups on the basis of their BMI as per the criteria of Asian Indian guideline [23]; Healthy (normal): 18.5-22.9 Kg/m2, Overweight: 23-24.9 Kg/m2 and Obese: ≥25 Kg/m2. As per WHO data on body fat, it was found that Asians have higher body fat for same age, sex and BMI compared to whites. Also, the proportion of Asian people with risk factors for type 2 diabetes and cardiovascular disease is substantial even below the existing WHO BMI cut-off point of 25 kg/m2. Thus, on the basis of Asian guidelines, approx 15% of Indian population may be overweight and require appropriate management. These guidelines were revised after discussions and consensus formed by Prevention and Management of Obesity and Metabolic Syndrome Group [22,23].
This study was approved by the IEC, GMC, Bhopal, letter no.10026/MC/IEC/2018, dated-12/04/2019 and written informed consent was obtained from all the participants.
Five milliliter venous blood sample was collected under aseptic condition in a plain sterile vial after fasting. The estimation of lipid profile (total cholesterol, HDL-C, LDL-C, VLDL-C and triglyceride) was done by Fully Automated Analyser (BA 400, BioSystem). The estimation of serum total T3, total T4 and TSH was done by Enzyme Linked Immunosorbent Assay (ELISA) method. The ELISA procedure was carried out through the commercially available ELISA kits (Rapid Diagnostic Pvt., Ltd.,). Anthropometric measurements such as body weight, height, WC and HC were measured in all subjects and BMI was calculated by weight (kg) divided by height (m2) and WHR was also calculated [20].
Statistical Analysis
Statistical analysis of the data was done using SPSS Software (version 20.0). Student’s t-test and ANOVA test were used for comparison of data in different groups. Correlation analysis was done by calculation of Pearson’s correlation coefficient (r). Statistical significance was considered as the p<0.05.
Results
Out of total 100 subjects, 42 were male, and 58 were female. Female subjects were having more weight as compared to male subjects [Table/Fig-1].
Gender distribution of study groups.
| Gender | Total (n=100) | Normal (n=33) | Overweight (n=36) | Obese (n=31) |
|---|
| Male | 42 | 13 | 14 | 15 |
| Female | 58 | 20 | 22 | 16 |
Data are presented in n: Number
Out of total 100 subjects, 33 were normal, 36 were overweight and 31 were found in obese group. Higher frequency was found in age group between 31 to 40 years as compared to other age groups [Table/Fig-2].
Age distribution of study subjects based on BMI.
| Age (Year) | Total (n=100) | Normal (n=33) | Overweight (n=36) | Obese (n=31) |
|---|
| 20-30 | 30 | 08 | 10 | 12 |
| 31-40 | 49 | 18 | 17 | 14 |
| 41-50 | 13 | 04 | 06 | 03 |
| 51-60 | 08 | 03 | 03 | 02 |
Data are presented in n: Number
The height, weight, BMI, WC, HC, Total Cholesterol, triglyceride, LDL-C was found significantly increased in overweight and obese subjects as compared to normal subjects. However, no significant difference for WC, HC, total cholesterol, triglyceride, LDL cholesterol was found between overweight and obese subjects [Table/Fig-3].
Anthropometric characteristics and biochemical parameters in study groups.
| Parameter (s) | Normal (n=33) Mean±SD | Overweight (n=36) Mean±SD | Obese (n=31) Mean±SD | *p-value | #p-value | $p-value |
|---|
| Height (m) | 1.54±0.96 | 1.59±0.06 | 1.49±0.07 | 0.049 | 0.001 | 0.001 |
| Weight (kg) | 53.7±6.6 | 62.7±5.4 | 78.4±14.2 | 0.001 | 0.001 | 0.001 |
| BMI (Kg/m2) | 21.4±1.45 | 24.54±1.18 | 34.6±4.3 | 0.001 | 0.001 | 0.001 |
| Waist circumference (cm) | 35.0±4.25 | 37.63±4.24 | 41.07±4.77 | 0.0112 | 0.001 | 0.232 |
| Hip circumference (cm) | 39.2±3.75 | 42.3±3.88 | 45.48±5.20 | 0.0012 | 0.001 | 0.066 |
| WHR | 0.89±0.07 | 0.90±0.04 | 0.91±0.04 | 0.671 | 0.295 | 0.344 |
| SBP (mm Hg) | 122.9±11.0 | 121.6±11.7 | 125.9±10.9 | 0.632 | 0.298 | 0.133 |
| DBP (mm Hg) | 83.2±8.9 | 85.7±10.0 | 88.4±8.0 | 0.287 | 0.184 | 0.271 |
| Blood glucose (mg/dL) | 107.4±20.4 | 105.7±20.0 | 111.0±21.0 | 0.394 | 0.345 | 0.912 |
| Total cholesterol (mg/dL) | 238.8±41.6 | 281.1±22.8 | 282.1±19.3 | 0.001 | 0.001 | 0.952 |
| Triglyceride (mg/dL) | 159.0±37.2 | 200.6±26.3 | 193.9±22.9 | 0.001 | 0.001 | 0.282 |
| HDL cholesterol (mg/dL) | 41.9±7.6 | 41.7±8.9 | 41.2±6.0 | 0.722 | 0.692 | 0.795 |
| LDL cholesterol (mg/dL) | 165.3±40.6 | 199.9±23.8 | 202.1±19.7 | 0.001 | 0.001 | 0.697 |
| VLDL cholesterol (mg/dL) | 32.1±7.8 | 40.1±5.3 | 38.7±4.5 | 0.394 | 0.345 | 0.912 |
Data are presented in Mean±SD, n: Number; BMI: Body mass index; WHR: Waist hip ratio; SBP: Systolic blood pressure, DBP: Diastolic blood pressure, p<0.05 was considered as significant level, *Comparison between normal and overweight subjects, #Comparison between normal and obese subjects, $Comparison between overweight and obese subjects; LDL: Low-density lipoprotein cholesterol, HDL: High-density lipoprotein cholesterol; VLDL: Very low-density lipoprotein cholesterol
The TSH levels were found significantly increased in overweight and obese subjects as compared to normal subjects, also a statistically significant difference was found for TSH levels between overweight and obese subjects. While total T3 and total T4 were not found statistically significant in study subjects [Table/Fig-4].
Serum total T3, T4 and TSH levels in study subjects.
| Thyroid profile | Normal (n=33) Mean±SD | Overweight (n=36) Mean±SD | Obese (n=31) Mean±SD | *p-value | #p-value | $p-value |
|---|
| Total T3 (ng/mL) | 2.51±1.4 | 2.19±0.76 | 2.10±0.51 | 0.246 | 0.147 | 0.147 |
| Total T4 (μg/dL) | 9.14±2.5 | 10.1±3.45 | 9.12±2.24 | 0.191 | 0.916 | 0.171 |
| Total TSH (μIU/mL) | 3.55±1.77 | 5.14±1.8 | 7.38±3.7 | 0.001 | 0.001 | 0.002 |
Data are presented in Mean±SD, n: Number, p<0.05 was considered as significant level, *Comparison between normal and overweight subjects, #Comparison between normal and obese subjects, $Comparison between overweight and obese subjects
Out of 100 subjects, 88% were euthyroid, 10% were shown hypothyroidism and 2% were shown hyperthyroidism [Table/Fig-5].
Distribution of thyroid dysfunction in study groups.
| Thyroid status (n=100) | % | Normal (18.5-22.9 kg/m2) (n=33) | Overweight (23-24.9 kg/m2) (n=36) | Obese (>25 kg/m2) (n=31) |
|---|
| Euthyroid (n=88) | 88% | 32 | 32 | 24 |
| Hypothyroid (n=10) | 10% | 01 | 03 | 06 |
| Hyperthyroid (n=02) | 02% | 00 | 01 | 01 |
Data are presented in n: Number and %: Percentage
Pearson’s correlation between BMI and T3, T4 and TSH were not significant found in normal subjects as well as obese subjects. There was a significant positive correlation between the BMI and T3 and between BMI and T4 in overweight subjects. However, correlation between BMI and TSH was not found significant in these subjects [Table/Fig-6].
Pearson’s correlation between BMI and T3, T4, and TSH.
| BMI with T3 | BMI with T4 | BMI with TSH |
|---|
| r | p | r | p | r | p |
|---|
| Normal (n=33) | 0.19 | 0.289 | -0.004 | 0.982 | -0.009 | 0.960 |
| Overweight (n=36) | 0.58 | 0.001 | 0.54 | 0.003 | 0.08 | 0.630 |
| Obese (n=31) | 0.33 | 0.804 | 0.24 | 0.209 | 0.23 | 0.230 |
p<0.05 was considered as significant level, r: Pearson’s correlation coefficient
Discussion
In the present study, anthropometric indices such as weight, WC, HC and BMI were found to be increased in obese group. Authors also calculated WHR, which is also important factor but no statistically significant difference was found among study subjects. In biochemical characteristics such as total cholesterol, triglycerides and LDL-C were significantly increased in obese subjects as compared to normal subjects. Ozsenel EB et al., supported our finding that triglyceride levels of obese subjects were high and HDL cholesterol levels were low when compared its levels in normal subjects [24]. Authors also found higher glucose level in obese subjects but no statistically significant difference was found in obese subjects as compared to normal subjects. There are several studies which supported the notion that atherogenic lipid and blood glucose level are higher in subjects who are overweight or obese [25,26]. These results suggest that thyroid dysfunction should be taken into account when evaluating and treating dyslipidemic patients.
In the present study, TSH level was significantly higher in overweight and obese subjects as compared to normal subjects, while no difference was noted in the total T3 or total T4 levels. In support to this study Muscogiuri G et al., have also reported higher TSH values in overweight and obese subjects [26]. Rotondi M et al., has mentioned that the impact of bodyweight on thyroid differs according to lower grade of overweight and obesity [27]. In the present study, total 12% thyroid dysfunction including 2% hyperthyroidism and 10% hypothyroidism was found in Indian healthy adults. The important finding of this study is that higher frequency of hypothyroidism in subjects was noted in obese group as compared to other groups. In support to present findings, Alkac C et al., suggested that thyroid dysfunction especially hypothyroidism was more common in obese subjects [28]. The differences between prevalence rates of hypothyroidism in obese subjects in different studies might be due to the variation in race, type of obesity and study settings between samples.
In the present study, on investigating relationship between BMI and thyroid hormones, we did not find any significant association between thyroid stimulating hormones and BMI in the study subjects. The study also did not find any correlation between BMI with T3 and BMI with T4 in obese subjects. In contrast to present results, Knudsen N et al., have reported a positive association between BMI with TSH and a negative association between BMI and fT4 [29]. Contrary to present results, TSH levels were found to be increased and positively correlated with BMI in obese adults in the study of Iacobellis G et al., however, they recruited only women subjects in there study [30]. Other studies supported the present results [31-33]. This study failed to find an association between BMI and thyroid function in the subjects which might be due to unaccounted confounding factors such as iodine intake, smoking, types of obesity and insulin sensitivity levels. However, the nature and biochemical basis of relationship between thyroid status and body composition rests indistinct. Longitudinal studies prove that weight gain is attended by increased TSH [34] and weight loss is associated to reduced TSH and decreased free T3 (FT3) levels [35]. Raises in TSH and FT3, but not FT4, have also been detected in obese individuals [36,37]. Lately, studies have also shown that in healthy euthyroid adults FT3 is positively associated with BMI [38,39]. The present study is suggesting the early stage and routine health check-up for thyroid dysfunction in normal healthy adults. Early stage detection will be helpful to minimise the burden of thyroid disorders in the population.
Limitation(s)
The study consists of small sample size. Other thyroid related parameters such as Thyroid Peroxidase (TPO) antibodies and free T3, free T4 levels were not assessed in this study. Also, the study did not compare thyroid function tests with lipid profile parameters in BMI categories.
Conclusion(s)
In conclusion, the study showed that thyroid function might be one of the important factors that influences body weight thereby obesity. The early stage screening of thyroid function tests with increasing body weight will be helpful in early intervention in obese peoples and management of obesity. Further large scale studies are needed to confirm the relationship between TSH, T3 and T4 with BMI in Indian obese adults.
Data are presented in n: NumberData are presented in n: NumberData are presented in Mean±SD, n: Number; BMI: Body mass index; WHR: Waist hip ratio; SBP: Systolic blood pressure, DBP: Diastolic blood pressure, p<0.05 was considered as significant level, *Comparison between normal and overweight subjects, #Comparison between normal and obese subjects, $Comparison between overweight and obese subjects; LDL: Low-density lipoprotein cholesterol, HDL: High-density lipoprotein cholesterol; VLDL: Very low-density lipoprotein cholesterolData are presented in Mean±SD, n: Number, p<0.05 was considered as significant level, *Comparison between normal and overweight subjects, #Comparison between normal and obese subjects, $Comparison between overweight and obese subjectsData are presented in n: Number and %: Percentagep<0.05 was considered as significant level, r: Pearson’s correlation coefficient
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