Subclinical hypothyroidism (SCH) is an asymptomatic condition associated with increased thyroid stimulating hormone (TSH) > 4 mIU/L with normal thyroxine (T4) and triidothyronine (T3) levels. It is more common in older subjects and especially in women with an overall incidence of 10%.
Because the normal TSH levels increase with age up to 7.5 mIU/L in older people, several studies have reported either no benefits whereas other have reported benefits of treatment. These studies have caused a great debate over the treatment of SCH, especially in older subjects. Therefore, the objective of this study was to review the current evidence over this debate by reviewing the recent literature on the subject to discern whether treatment of SCH is necessary and under what circumstances.
In order to get a better perspective on the current debate over treatment of SCH, a focused Medline search of the English language literature from 2012 to 2019 using the terms, hypothyroidism, subclinical, dyslipidemia, cardiovascular disease, heart failure, and 38 papers with pertinent information were selected.
The analysis of results from these papers indicated that the normal levels of TSH are increasing with the advancement of age from 4 mIU/L up to 7.5 mIU/L for patients ≥ 75 years of age. Also, several of reviewed studies have shown no benefits of treatment whereas, other have shown definite benefits of treatment with levothyroxine supplementation on the clinical and metabolic effects of SBH with reductions in CVD, HF, and mortality. The treatment is more effective in younger persons and less so in older persons.
Based on the overall evidence, treatment of SCH is indicated in younger persons with a TSH level > 4.0 mIU/L. In older subjects, treatment should be individualized and based on the presence of symptoms, the level of TSH, and initiated at TSH levels ≥ 10 mIU/L and at low doses to avoid adverse cardiovascular effects from overtreatment.

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