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HYPOTHYROIDISM
Treatment of subclinical hypothyroidism slightly reduces risk of heart problems
BACKGROUND
Overt hypothyroidism, or underactive thyroid, is diagnosed with thyroid hormone levels (FT4) are low and TSH levels are high. Subclinical hypothyroidism (SCH) is defined as a mild form of hypothyroidism where the only TSH level is high but the FT4 level is in the normal range. The American Thyroid Association (ATA) and the U.K. National Institute for Health and Care Excellence (NICE) advise treatment only when the TSH level is above 10 mU/L. However, the ATA, American Association for Clinical Endocrinology (AACE) and NICE recommend treatment with TSH <10 mU/L only in specific cases, such as symptoms, evidence of autoimmune disease or cardiovascular risk factors.
Some studies showed that treating SCH can reduce cholesterol plaque formation and decrease the thickness of the carotid artery. Conversely, this was not demonstrated in patients over 65 years with SCH taking levothyroxine (L-T4), with no decrease in cardiovascular events and death from all-causes. Therefore, the use of L-T4 in decreasing cardiovascular outcomes in patients with SCH remains controversial. This study aimed to conclude whether L-T4 replacement affects the risk of major adverse cardiovascular events in patients with SCH.
THE FULL ARTICLE TITLE
Yu OUY, et al. Levothyroxine treatment of subclinical hypothyroidism and the risk of adverse cardiovascular events. Thyroid. Epub 20204 Aug 2024; doi: 10.1089/ thy.2024.0227. PMID: 39104265.
SUMMARY OF THE STUDY
Information was collected from the Clinical Practice Research Datalink Aurum database between 1998 and 2018, which includes over 40 million individuals in over 1700 general practices in the United Kingdom.
The study involved patient18 years of age or older with newly diagnosed SCH and TSH measurements between 5 and 10 mU/L on different dates within 1 year. The study included 76,946 patients with SCH treated with levothyroxine and 76,946 patients with SCH not treated. The average age was 62.8 years, and the majority of the participants, at 76.5%, were women. Patients were followed at 1.6 years and 2.5 years. The occurrence of major adverse cardiovascular events was 12.8 per 1000 person-years in the treated group and 13.9 per 1000 person-years in the untreated group.
L-T4 treatment was connected with a small decrease in the risk of major adverse cardiovascular events, with a decrease in the risk of nonfatal heart attacks and cardiacrelated death, as well as death from all causes. However, the association between L-T4 treatment and risk of major adverse cardiovascular events was similar in groups with TSH levels between 5 mU/L and 8 mU/L and TSH levels between 8.1 mU/L and 10 mU/L. In addition, average TSH and thyroxine levels were alike during follow-up in patients treated and untreated with L-T4.
WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study showed that L-T4 therapy in patients with SCH was linked with a 12% reduction in the risk of major adverse cardiovascular events, though contradictory results were found. Even though there was a mild decrease in major adverse cardiovascular events in the group treated with L-T4, it is challenging to say there was any difference between L-T4 therapy and the risk of major adverse cardiovascular events in all groups. Therefore, it is reasonable to consider therapy with L-T4 in patients with mild SCH and increased cardiac risk factors after a discussion with the patient.
— Joanna Miragaya, MD
ATA RESOURCES
Hypothyroidism (Underactive): https://www.thyroid.org/hypothyroidism/
Thyroid Function Tests: https://www.thyroid.org/thyroid-function-tests/
Thyroid Hormone Treatment: https://www.thyroid.org/thyroid-hormone-treatment/
ABBREVIATIONS & DEFINITIONS
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.
Overt Hypothyroidism: clear hypothyroidism an increased TSH and a decreased T4 level. All patients with overt hypothyroidism are usually treated with thyroid hormone pills.
Levothyroxine (T4): the major hormone produced by the thyroid gland and available in pill form as Synthroid™, Levoxyl™, Tyrosint™ and generic preparations.
Thyroid Hormone Therapy: patients with hypothyroidism are most often treated with Levothyroxine in order to return their thyroid hormone levels to normal. Replacement therapy means the goal is a TSH in the normal range and is the usual therapy. Suppressive therapy means that the goal is a TSH below the normal range and is used in thyroid cancer patients to prevent growth of any remaining cancer cells.
Thyroxine (T4): the major hormone produced by the thyroid gland. T4 gets converted to the active hormone T3 in various tissues in the body.
Triiodothyronine (T3): the active thyroid hormone, usually produced from thyroxine, available in pill form as Cytomel™.
Thyroid Stimulating Hormone (TSH): 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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