J Endocrinol Metab
Journal of Endocrinology and Metabolism, ISSN 1923-2861 print, 1923-287X online, Open Access
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Original Article

Volume 2, Number 3, June 2012, pages 105-109


Thyroid Volume Predicts Body Mass Index 2 and 6 Years Later

Daniel Litu Chena, b, g, Katherine Tonksa, b, Jerry R. Greenfielda, b, Charles El-Noutyc, Serge Hercbergc, d, Sebastien Czernichowe, f

aDepartment of Endocrinology, St Vincent’s Hospital, Sydney, Australia
bGarvan Institute of Medical Research and University of New South Wales, Sydney, Australia
cUMR (INSERM U557, INRA, CNAM, UP13), Universite Paris 13, Bobigny, France
dDepartement de Sante Publique, Hopital Avicenne, Bobigny, France
eNutrition Departement, Hopital Ambroise Pare, Boulogne-Billancourt, France
fUniversite Versailles St-Quentin, Boulogne-Billancourt, France
gCorresponding author: Daniel Li Tu Chen

Manuscript accepted for publication June 20, 2012
Short title: Thyroid Volume Predicts Body Mass Index
doi: https://doi.org/10.4021/jem99w

Abstract▴Top 

Background: Thyroid volume correlates positively with body mass index (BMI). This correlation holds true for both iodine-sufficient and mild/moderate iodine-deficient areas. We examined the association between thyroid volume and BMI and change in BMI over 4 years in middle-age adults recruited from the general population.

Methods: A total of 2,495 subjects, for whom thyroid volume, FT4 and TSH were available (women aged 35 - 60 years and men aged 45 - 60 years), were derived from the Supplementation en Vitamines et Mineraux Antioxydants (SU.VI. MAX) cohort study conducted in France since baseline (1994). Weight and height were measured 2 and 6 years after inclusion. Linear univariate and multiple regression analyses were performed to evaluate correlations between thyroid volume and BMI at 2 and 6 years and BMI change from year 2 to 6.

Results: Baseline thyroid volume was positively correlated with BMI at 2 years (men: β = 0.09, P < 0.01; women: β = 0.09, P < 0.01) and 6 years after inclusion (men: β = 0.10, P < 0.01; women: β = 0.09, P < 0.01). The correlation between thyroid volume and BMI at 2 and 6 years remained significant after adjusting for free T4, TSH, gender, age, smoking, alcohol consumption and TSH-thyroid volume interaction factor (β = 0.11, P <0.01). Baseline thyroid volume was not correlated with BMI change from year 2 to 6 in linear regression analysis.

Conclusion: In French adults, thyroid volume predicted BMI at 2 and 6 years. Further studies are needed to explore the association between thyroid volume and BMI.

Keywords: Body mass index; Thyroid volume; Weight change; Population study

Introduction▴Top 

Observational epidemiological studies have reported a positive correlation between thyroid volume and body weight [1], body mass index (BMI) [2, 3], body surface area [2] and lean body mass [4]. These correlations are observed in both iodine-sufficient and mild/moderate iodine-deficient areas [1, 3, 5]. However, studies are cross-sectional and cannot define causality. To date, there have been no studies that have examined the association between thyroid volume and BMI a number of years later.

We examined the correlation between thyroid volume and BMI 2 and 6 years later in a group of middle-age adults participating to the Supplementation en Vitamines et Mineraux Antioxydants (SU.VI.MAX) French cohort.

Materials and Methods▴Top 

Subjects

We undertook an analysis of data collected in the SU.VI.MAX study. This study was conducted in France. Subjects were participants of the SU.VI.MAX study, initially designed as a randomized, double-blind, placebo-controlled, primary prevention trial to test the potential efficacy of daily supplementation with antioxidant vitamins and minerals at nutritional doses (ascorbic acid, vitamin E, beta-carotene, selenium and zinc) on the risk of cancer, ischemic heart diseases and total mortality. The design and rationale of the SU.VI.MAX study (Supplementation en Vitamines et Mineraux Antioxydants) have been extensively detailed previously [6]. Eligible subjects, 7,713 women aged 35 - 60 years and 5,028 men aged 45 - 60 years at baseline, were included in 1994 - 1995 and followed up for 7.5 y [7]. During the follow-up, all participants underwent an annual visit, with alternating blood sampling (at baseline) or clinical examination (1995 - 1996), every other year. They also provided information regarding health, diet, drugs and various lifestyle indicators. On a subsample of 3,523 subjects, thyroid volume was assessed at baseline, through the use of a mobile unit (‘ThyroMobil van’), equipped with an ultrasound machine. We analysed the relationship between thyroid volume and weight and BMI at 2 and 6 years. Twenty-one percent of male subjects and 13% of female subjects did not have weight measurement 2 and 6 years after inclusion. Thus, 1,001 men and 1,494 women completed weight and height measurement 2 and 6 years after inclusion.

Several exclusion criteria were applied: goitre, signs of previous or current thyroid disease, treatment with thyroid hormones, antithyroid drugs and lithium treatment. Twenty subjects with urinary iodine concentration ≥60 µg/100 mL were eliminated, as was one subject with thiocyanate overload (urinary thiocyanate concentration≥ 50 mg/L). The final study group consisted of 1,274 men and 1,713 women.

The SU.VI.MAX study was approved by the Ethical Committee for Studies with Human Subjects of the Paris-Cochin Hospital (CCPPRB No. 706) and the “Commission Nationale Informatique et Liberté” (CNIL No. 334641), which ensures that medical information be kept confidential and anonymous.

Thyroid volume

Thyroid volume was estimated using a high frequency 7.5 MHz linear array transducer (Sonoline SI-400, Siemens, Erlangen, Germany). The examination was performed with the patient in a supine position with the neck hyperextended. The isthmus was not taken into account in volume calculation. Nodules and/or cystic areas were included in volume determination. All ultrasonographic examinations were performed and interpreted by the same radiologist.

Anthropometry

Weight was measured 2 and 6 years after inclusion with an electronic scale (Seca, Germany) with subjects in indoor clothing and no shoes. Height was measured with a wall-mounted stadiometer with no shoes to the nearest 0.5 cm. BMI was calculated as weight divided by height squared (kg/m2).

Statistical analysis

Men and women were evaluated separately. The relationship between baseline thyroid volume and BMI at 2 and 6 years was estimated by linear univariate analysis. Multiple linear regression was used to adjust for potential confounders including age, TSH, free T4, alcohol and tobacco consumption to consolidate the relationship between baseline thyroid volume and BMI at 2 and 6 years. Data were analysed using ‘version 9.1’ SAS statistical software (SAS Institute, Cary, USA).

Results▴Top 

Baseline thyroid volume, TSH, free T4 (fT4) and BMI 2 and 6 years after inclusion are shown in Table 1. Mean BMI 2 years after inclusion was 25.3 ± 2.9 kg/m2 in men and 22.8 ± 3.3 kg/m2 in women; mean BMI 6 years after inclusion was 26.0 ± 3.1 kg/m2 in men and 23.6 ± 3.6 kg/m2 in women. The mean weight change between the 2nd and 6th years was 2 ± 5.4 kg. Mean thyroid volume at inclusion was 11.5 ± 5 mL. The median thyroid volume was 13.2 mL in men and 9.1 mL in women.

Table 1.
Click to view
Table 1. Characteristics of SU.VI.MAX Cohort
 

Baseline thyroid volume was positively correlated with BMI 2 years (men: β = 0.09, P < 0.01; women: β = 0.09, P< 0.01) and 6 years (men: β = 0.01, P <0.01; women: β = 0.09, P < 0.01) after inclusion (Table 2). In the total cohort, correlations between baseline thyroid volume and BMI at 2 and 6 years remained significant after adjusting for gender, age, TSH, fT4, smoking and alcohol consumption (BMI 2 years: β = 0.11, P < 0.01; BMI 6 years: β = 0.11, P < 0.01).

Table 2.
Click to view
Table 2. Linear Regression Analysis of BMI 2 and 6 Years After Inclusion With Baseline Characteristics (n = 2,413)
 

Baseline TSH was negatively correlated with weight change (β = -0.25, P < 0.01), but not thyroid volume (P =0.77) or free T4 (P = 0.96). The correlation between TSH and weight change was eliminated after adjusting for other variables including gender, free T4, alcohol/tobacco consumption (men: P = 0.84, women: P = 0.88).

Discussion▴Top 

Our study demonstrates that thyroid volume is positively correlated with BMI at 2 and 6 years, even after adjusting for other variables, such as fT4, TSH, gender and age. This is the first study to examine the correlation between thyroid volume and BMI 2 and 6 years later. Previous studies have evaluated the association between thyroid volume and BMI or body weight at one point in time (Table 3). These studies have all demonstrated a positive correlation between thyroid volume and BMI/body weight.

Table 3.
Click to view
Table 3. Literature Review of Correlation Between Thyroid Volume and Body Weight or BMI
 

Our study did not show any significant correlation between baseline thyroid volume and weight change between 2 and 6 years. Although TSH correlated negatively with weight change, this correlation became insignificant after adjusting for other confounders. The lack of marked weight change over 4 years may undermine any possible significant correlation between thyroid volume and weight change. Other explanations could be due to the low heterogeneity in the study population and a short follow-up period between measurements. Two studies have examined the effect of weight loss on thyroid volume changes. Sari [8] examined intentional weight loss over 6 months using sibutramine 15 mg/day and/or orlistat 360 mg/day and its effect on thyroid volume. Wesche [9] evaluated correlation between 6 months of intensive rowing training and thyroid volume in lean subjects. Both studies achieved significant weight loss (> 10% of body weight and mean weight loss of 2.5 kg respectively) and demonstrated a positive correlation between weight loss and reduction in thyroid volume.

Our study had some limitations. Firstly, thyroid volume was only measured at baseline. Secondly, as this was an observational study, we cannot draw causal inferences regarding to the association between thyroid volume and BMI. Therefore, there may be potential confounders that contribute to BMI other than baseline thyroid volume.

In summary, our study shows that baseline thyroid volume predicts BMI 2 and 6 years later. Further studies are needed to explore the association between thyroid volume, and BMI.

Acknowledgments

We thank Stephen Besseau, UMR (INSERM U557, INRA, CNAM, UP13), Universite Paris 13, Bobigny, France for his support in performing statistical analysis.

Conflict of Interest

All authors declare no conflict of interest.


References▴Top 
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