Clinical Thyroidology® for the Public

Summaries for the Public from recent articles in Clinical Thyroidology
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HYPOTHYROIDISM
What is the effect of age on the frequency of subclinical hypothyroidism?

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BACKGROUND
Hypothyroidism is common. Overt hypothyroidism is diagnosed with an increased TSH and a low FT4 and is treated with thyroid hormone therapy, usually levothyroxine. The most common cause of overt hypothyroidism in the United Stated is autoimmune thyroid disease, where the body produces antibodies that attack and destroy the thyroid. Subclinical hypothyroidism is diagnosed with an increased TSH and normal FT4 and treatment with thyroid hormone is less clear and often controversial.

Thyroid levels vary with age, and several studies have shown that a large majority of people over 80 years old have a TSH above 7 mIU/L, which is mildly increased based on the standard TSH reference range. Further, subclinical hypothyroidism is present in 19.09% of the population over the age of 70 years. It is unclear if this represents a disease that should be treated or a variant related to normal aging. Thus, it is debated whether a more specific age reference range TSH should be used for the older population. Besides, the immune responses change with aging, and the levels of thyroid antibodies may also. In this study, the authors examined the changes in thyroid function and thyroid antibodies in the older population, and whether it affects the diagnosis of thyroid disease.

THE FULL ARTICLE TITLE
 Razvi SS et al. Changes in thyroid function and autoimmunity in older individuals: longitudinal analysis of the Whickham cohort. J Clin Endocrinol Metab. Epub 2024 Dec 14:dgae875; doi: 10.1210/clinem/dgae875. PMID: 39673773.

SUMMARY OF THE STUDY
The Whickham cohort is a random population of individuals living in Whickham, England, who have been followed over many years to study development of disease. In particular, thyroid hormone levels have been followed in this group over the years. Of 1704 survivors of the Whickham cohort, a total of 204 remained for the study after attending a baseline visit between 2008 and 2012 and a follow-up visit between 2016 and 2019. Thyroid function levels were assessed as the change in TSH, FT4, and FT3 levels between baseline and follow-up values.

The average age of the individuals was 77.0 and 55.9% were female. The follow-up average was 7.8 years. The results showed that the serum TSH concentration increased from 1.94 mIU/L to 2.18 mIU/L over this time period, while FT4 remained similar and FT3 concentration decreased slightly. At the beginning of the study, 3.5 % of patients were diagnosed with subclinical hypothyroidism. Throughout 7.8 years of follow-up, patients with subclinical hypothyroidism increased to 9.0% when using standard TSH reference ranges (0.3–4.5 mU/L), but it decreased to 2% when using the visit-specific reference ranges (0.54–6.28 mU/L). Thyroid antibodies also decreased significantly over the period of time.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that TSH levels increase and thyroid antibodies decrease with aging. Therefore, it is important to develop and use more age-appropriate TSH reference ranges to avoid overdiagnosis and overtreatment of hypothyroidism in older adults.

— Joanna Miragaya, MD

ABBREVIATIONS & DEFINITIONS

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).

TPO antibodies: these are antibodies that attack the thyroid instead of bacteria and viruses, they are a marker for autoimmune thyroid disease, which is the main underlying cause for hypothyroidism and hyperthyroidism in the United States.

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

Subclinical Hypothyroidism: a mild form of hypothyroidism where the only abnormal hormone level is an increased TSH. There is controversy as to whether this should be treated or not.

Thyroxine (T4): the major hormone produced by the thyroid gland. T4 gets converted to the active hormone T3 in various tissues in the body.

TSH: thyroid stimulating hormone — produced by the pituitary gland that regulates thyroid function; also the best screening test to determine if the thyroid is functioning normally.

 

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