August 29, 2016
2 min read

Subclinical hypothyroidism ‘benign state’ in older adults

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In older adults, variations in thyroid-stimulating hormone levels that are within the reference range are not associated with all-cause or vascular mortality, according to recent findings.

In a prospective, observational study, researchers also found that, in older men, lower serum TSH predicted disability, whereas higher serum reverse triiodothyronine predicted disability in older women.

“There is a real paucity of high-quality data concerning management of borderline thyroid function tests, particularly in older people,” Simon H. S. Pearce, MD, MBBS, FRCP, professor of applied epidemiology at the Institute of Health & Society at Newcastle University, United Kingdom, told Endocrine Today. “Nevertheless, physicians are frequently tempted to ‘tamper’ when the lab result shows a serum TSH marginally above the reference range, as levothyroxine is correctly perceived as a cheap and very safe medication. The patient often feels good because something has been done, and the doctor feels they are doing something simple and appropriate; but is treating mild or subclinical hypothyroidism in older people really benefiting them?”

Pearce and colleagues analyzed data from 643 adults aged 85 years participating in the Newcastle 85+ Study, a longitudinal study of health trajectories and outcomes in a single-year birth cohort (1921) in the United Kingdom. Participants, assessed in their own home or institution, underwent health exams, provided fasting blood samples and completed questionnaires; medical records were also reviewed to determine prevalence of 17 common diseases. Researchers followed the cohort for mortality and disability for up to 9 years; a disability score was created from 17 activities of daily living at baseline and at 18, 36 and 60 months. Primary outcomes were all-cause mortality, cardiovascular mortality and disability according to thyroid disease status and baseline thyroid hormone parameters (serum TSH, free thyroxine, free T3 and reverse T3); models were adjusted for age, sex, education, BMI, smoking and disease count.

Within the cohort, 83.1% were euthyroid at baseline, 12.5% had subclinical hypothyroidism, 2.9% had subclinical hyperthyroidism and 0.81% were overtly hyperthyroid.

Researchers did not find an association between thyroid status and all-cause mortality or CV mortality after adjustments. In an unadjusted analysis of individual serum thyroid hormones, researchers found that all-cause mortality was negatively associated with free T3 (HR = 0.81; 95% CI, 0.73-0.91) and positively associated with reverse T3 (HR = 1.23; 95% CI, 1.12-1.34), but only the association with reverse T3 persisted after adjustments for education, BMI, smoking status and disease count.

Although the researchers could not confirm that it is beneficial to have an elevated TSH level, Pearce said he found no evidence that an elevated serum TSH was detrimental, adding that it was “quite safe” to monitor the situation.

“We find that baseline serum TSH had no substantial association with all-cause or vascular mortality in our cohort, which confirms the findings of many previous studies, albeit in a cohort of older participants,” the researchers wrote. “These findings, therefore, provide further reassurance that subclinical hypothyroidism is a benign state in advanced older age.”

In separate analyses for men and women, there was a trend toward increasing disability with decreasing levels of TSH and free T3 and increasing levels of reverse T3 in women followed for 60 months; only the association with reverse T3 persisted after adjustment. In men, decreasing levels of TSH predicted increased disability over 60 months.

“Our study is reassuring that individuals aged 85 years with both subclinical hypothyroidism and subclinical hyperthyroidism do not have a significantly worse survival over 9 years than their euthyroid peers,” the researchers wrote. “However, thyroid function tests did predict disability, with higher serum TSH levels predicting better outcomes. These data strengthen the argument for routine use of age-specific thyroid function reference ranges.” – by Regina Schaffer

Disclosure: Pearce reports receiving speaking fees from Merck and consulting for ViroPharma and Shire.