Related Experiment Video
Updated: Mar 29, 2026

Author Spotlight: In Vivo Assessment of Thyroid Hormone Disruption Using the THAI Mouse Model
Published on: October 6, 2023
Paradoxical Relationship Between Body Mass Index and Thyroid Hormone Levels: A Study Using Mendelian Randomization
Peter N Taylor1, Rebecca Richmond1, Neil Davies1
1Thyroid Research Group (P.N.T., O.O., J.W.G., C.M.D.) and Institute of Molecular and Experimental Medicine (A.R.), Cardiff University School of Medicine, Cardiff, CF14 4XN United Kingdom; Medical Research Council Integrative Epidemiology Unit (R.R., N.D., G.D.S., N.J.T.), University of Bristol, Bristol, BS8 2BN United Kingdom; Department of Social and Community Medicine (A.S., A.G., K.N., S.R.), University of Bristol, Bristol, BS8 2BN United Kingdom; Department of Biochemistry (K.S.), Bristol Royal Infirmary University Hospitals Bristol National Health Service Foundation Trust, Bristol, BS2 8HW United Kingdom; Geschäftsleiter Medizinisches Versorgungszentrum Labor Dr. Reising-Ackermann und Kollegen (W.W.), D-04289 Leipzig, Germany; Department of Biochemistry (A.T.), Royal United Hospital, Bath, BA1 3NG United Kingdom; Department of Non-Communicable Disease Epidemiology (D.N.), Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, CF14 4XN United Kingdom; Molecular Endocrinology Group (G.R.W.), Department of Medicine, Imperial College London, London, WC1E 7HT United Kingdom; and Musculoskeletal Research Unit (J.H.T.), University of Bristol, Learning and Research Southmead Hospital, Westbury on Trym, Bristol, BS10 5NB United Kingdom.
Higher childhood body mass index (BMI) causally increases free T3 (FT3) levels, potentially explaining observed associations. This finding is crucial given rising childhood obesity rates.
Area of Science:
- Endocrinology
- Genetics
- Pediatrics
Background:
- Free T3 (FT3) shows positive associations with body mass index (BMI) in healthy individuals.
- This contrasts with findings in pathological thyroid dysfunction, necessitating further investigation.
Purpose of the Study:
- To investigate the influence of childhood adiposity on free T3 (FT3) levels.
- To explore the causal relationship between BMI and FT3 using genetic data.
Main Methods:
- Employed Mendelian randomization analysis utilizing genetic variants strongly associated with BMI.
- Utilized data from the Avon Longitudinal Study of Parents and Children cohort.
- Analyzed thyroid function (FT3, FT4) and body composition (dual x-ray absorptiometry) in 3014 children with genetic data.
Main Results:
- Observationally, higher BMI at age 7 was associated with increased FT3 and decreased FT4 levels.
- Genetically determined increase in BMI was significantly associated with higher FT3 levels at age 7.
- No substantial change in free T4 (FT4) levels was observed with genetically determined BMI increase.
Conclusions:
- Childhood BMI and fat mass play a causal role in elevating FT3 levels.
- This causal link may resolve paradoxical associations seen in observational studies.
- The relationship between rising childhood obesity and FT3 warrants further attention.
Related Concept Videos
Regression Toward the Mean
Synthesis and Regulation of Thyroid Hormones
Upon reaching the thyroid gland, TSH stimulates the follicular cells' active uptake of iodide ions from the blood. The ions diffuse to the apical surface of the cells and are oxidized to iodine. The...
Functions of Thyroid Hormones
TH is indispensable for the normal development and maturation of the skeletal, muscular, and nervous systems during fetal and childhood growth. It facilitates bone mineral turnover and regulates protein synthesis in developing tissues, contributing significantly to overall growth and...
Study Designs in Epidemiology
Observational studies are those where the researcher does not intervene but rather observes natural variations. They include cross-sectional, cohort, and...
Confounding in Epidemiological Studies
Bias in Epidemiological Studies
