Levothyroxine did not ease symptoms in older adults with subclinical hypothyroidism
A randomised trial and a 21-study meta-analysis found thyroid hormone normalised the blood test but left tiredness and symptom scores unchanged. A guideline now advises against routine treatment.
For older adults whose blood tests show subclinical hypothyroidism — a raised thyroid-stimulating hormone with a normal thyroxine level, and usually no clear symptoms — starting levothyroxine did not relieve tiredness or hypothyroid symptoms in a large randomised trial, even though it normalised the blood test [s1]. A meta-analysis of 21 trials reached the same conclusion, and a clinical practice guideline now recommends against treating most such adults [s2][s3].
That gap — between a lab value that improves and a patient who does not feel any better — is the whole story of subclinical hypothyroidism, one of the most common reasons a healthy older person ends up on a lifelong daily pill.
What subclinical hypothyroidism is
It is a biochemical state, not a set of symptoms: thyrotropin above the reference range while free thyroxine stays within it [s1]. It is often found incidentally on a blood test. The clinical question is whether nudging the thyrotropin back to normal with levothyroxine actually helps the person, or merely tidies the number.
The TRUST trial
TRUST was a double-blind, randomised, placebo-controlled trial in 737 adults aged 65 or older with persisting subclinical hypothyroidism — thyrotropin of 4.60 to 19.99 mIU per litre, with free thyroxine in the reference range [s1]. It assigned 368 to levothyroxine, at a starting dose of 50 µg daily (or 25 µg for those under 50 kg or with coronary heart disease) with dose adjustment by thyrotropin level, and 369 to placebo with mock adjustment [s1]. The mean age was 74.4 years and 396 participants (53.7%) were women [s1].
The two primary outcomes were the change at one year in a Hypothyroid Symptoms score and a Tiredness score, each running from 0 to 100, with higher scores meaning more symptoms; the minimum clinically important difference was set at 9 points [s1].
The drug did what it is supposed to do chemically. The mean thyrotropin fell from 6.40 mIU per litre at baseline to 3.63 in the levothyroxine group, against 5.48 in the placebo group at one year (P<0.001), at a median dose of 50 µg [s1]. But the symptoms did not move. The change in the Hypothyroid Symptoms score was 0.2 in the placebo group and 0.2 in the levothyroxine group — a between-group difference of 0.0 (95% CI −2.0 to 2.1) [s1]. The Tiredness score changed by 3.2 and 3.8 respectively, a difference of 0.4 (95% CI −2.1 to 2.9) [s1]. Both are far short of the 9-point threshold, and neither reached significance. No benefit appeared on the secondary measures either, and there was no significant excess of serious adverse events [s1].
Not one trial — a body of evidence
The finding is not a one-off. A systematic review and meta-analysis in JAMA pooled 21 trials, with 2,192 adults randomised [s2]. Thyroid hormone therapy lowered mean thyrotropin into the normal range but was not associated with any benefit for general quality of life (n=796; standardised mean difference −0.11; 95% CI −0.25 to 0.03) or for thyroid-related symptoms (n=858; standardised mean difference 0.01; 95% CI −0.12 to 0.14) [s2]. The authors concluded the findings "do not support the routine use" of thyroid hormone therapy in adults with subclinical hypothyroidism [s2].
What the guideline says
On that evidence, a BMJ Rapid Recommendations panel issued a strong recommendation against thyroid hormones for almost all adults with subclinical hypothyroidism [s3]. It judged that the hormones have little or no effect on quality of life, thyroid-related symptoms, depressive symptoms, fatigue or body mass index, on moderate-to-high-quality evidence [s3]. The panel weighed those absent benefits against the burden of lifelong management and uncertainty about harms, and advised monitoring the thyroid rather than treating it [s3].
There are limits and exceptions. TRUST enrolled older adults with relatively mild elevations, and the evidence is weaker at thyrotropin levels above 20 mIU per litre, in younger adults, in pregnancy, and for people with marked symptoms — situations the guideline treats separately [s1][s3]. The result is about the common scenario: an incidental, mildly abnormal test in an older person who feels well.
What it means
The value of this evidence is in what it prevents: a reflexive prescription that normalises a number without changing how anyone feels, and then continues for years. Where a treatment fixes the test but not the patient, that is worth knowing before the pill is started.
This article describes research findings. It is not advice about any medicine, and nothing here should be used to start, stop or change treatment.
Sources
- Thyroid Hormone Therapy for Older Adults with Subclinical Hypothyroidism, New England Journal of Medicine, 3 April 2017
- Association of Thyroid Hormone Therapy With Quality of Life and Thyroid-Related Symptoms in Subclinical Hypothyroidism, JAMA, 2 October 2018
- Thyroid hormones treatment for subclinical hypothyroidism: a clinical practice guideline, The BMJ, 14 May 2019
Sources
- Thyroid Hormone Therapy for Older Adults with Subclinical Hypothyroidism — New England Journal of Medicine , April 3, 2017
- Association of Thyroid Hormone Therapy With Quality of Life and Thyroid-Related Symptoms in Patients With Subclinical Hypothyroidism: A Systematic Review and Meta-analysis — JAMA , October 2, 2018
- Thyroid hormones treatment for subclinical hypothyroidism: a clinical practice guideline — The BMJ , May 14, 2019
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