Clinical Thyroidology® for the Public

Summaries for the Public from recent articles in Clinical Thyroidology
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THYROID AND WEIGHT
Is obesity is associated with increased fat cells in the thyroid?

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BACKGROUND
Obesity has been associated with hypothyroidism and thyroid nodules. To date, there is not a clear link between obesity and thyroid disorders other than this association. One possible link is inflammation, which is present in both disorders. In hypothyroidism and thyroid nodules, antibodies that attack the thyroid cause the inflammation. This is known as autoimmune thyroid disease. In obesity, inflammatory cells enter into fat tissues and cause low-grade inflammation. Findings of an association between obesity, thyroid inflammation and autoimmune thyroid disease have been inconsistent. This study evaluated thyroid tissue from normal-weight, overweight, and obese individuals to assess potential differences in inflammation that might contribute to altered thyroid function in obesity.

THE FULL ARTICLE TITLE
 Basolo A et al 2021 Histological pattern and gene expression profiling of thyroid tissue in subjects with obesity. J Endocrinol Invest. Epub 2021 Aug 15. PMID: 34392500.

SUMMARY OF THE STUDY
Patients undergoing surgical treatment for thyroid nodules were included in this study. Patients with pre-existing autoimmune thyroid disease or a final diagnosis of thyroid cancer were removed from the study. The tissues were evaluated for the presence of fat cells inflammatory cells. In a subset of patients, the tissues were evaluated for genes that are associated with inflammation.

The study enrolled 98 patients (30 normal-weight, 34 overweight, 34 with obesity). Fat cells were seen within the thyroid gland in 55 individuals. Overall, fat cells in the thyroid were seen in 73.5% of the obese individuals, 52.9% of the overweight individuals and 40% in the normal weight individuals. The absolute number of fat cells within the thyroid increased directly with the increase in BMI. No differences in inflammatory cells in the thyroid was observed among groups, nor was there a significant association between fat cells and inflammatory cells within the thyroid. Further, there were some differences in gene expression in the thyroids from overweight and obese individuals as compared to normal weight individuals.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
In individuals without autoimmune thyroid disease, obesity is associated with increased fat cells and altered gene expression in the thyroid. These findings suggest a role for the associated inflammation seen in obesity in causing changes in thyroid structure and function. Further studies are needed to clarify the contribution of obesity to clinically relevant thyroid disorders and the development of thyroid nodules.

— Alan P. Farwell, MD

ABBREVIATIONS & DEFINITIONS

Body-mass index (BMI): a standardized measure of obesity calculated by dividing the weight in kilograms by the square of the height. A normal BMI is 18.5-24.9, overweight is 25-30 and obese is >30.

Autoimmune thyroid disease: a group of disorders that are caused by antibodies that get confused and attack the thyroid. These antibodies can either turn on the thyroid (Graves’ disease, hyperthyroidism) or turn it off (Hashimoto’s thyroiditis, hypothyroidism).

Hypothyroidism: a condition where the thyroid gland is underactive and doesn’t produce enough thyroid hormone. Treatment requires taking thyroid hormone pills.

Thyroid nodule: an abnormal growth of thyroid cells that forms a lump within the thyroid. While most thyroid nodules are non-cancerous (Benign), ~5% are cancerous.

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