Levothyroxine shows clear benefits on TC, LDL cholesterol in SCH patients
Levothyroxine demonstrates a lowering effect on total cholesterol (TC) and low-density lipoprotein (LDL) cholesterol in patients with subclinical hypothyroidism (SCH), including those with mild SCH, according to a systematic review and meta-analysis.
Researchers searched multiple electronic databases for randomized controlled trials evaluating the lipid-lowering effect of replacement therapy (eg, triiodothyronine [T3], thyroxine or both) in comparison with placebo or observation in SCH patients older than 18 years. Exclusion criteria included pregnancy, severe complications that influenced thyroid function or lipid metabolism, treatment with any other medicine that affected the thyroid or lipid metabolism during trials, and obviously poor compliance.
The primary outcomes investigated were changes from baseline in TC, LDL and high-density lipoprotein (HDL) cholesterol, and triglycerides. Subgroup analyses were performed to assess the effect of treatment duration, disease severity and ethnicity on the occurrence of discrepancy.
A total of 12 trials involving 940 participants were included in the final analysis. Compared with the control group, levothyroxine substitution yielded a significant reduction in TC (mean, −0.29 mmol/L; −0.42 to −0.16) and LDL cholesterol (mean, −0.22 mmol/L; −0.36 to −0.09), with no marked effects on HDL cholesterol (mean, −0.04 mmol/L; −0.08 to 0.01) or triglycerides (mean, −0.04 mmol/L; −0.08 to 0.00).
Pooled data from trials including only patients with mild SCH (thyrotropin <10 mIU/L) showed similar results, with the lipid-lowering effect of levothyroxine not significantly different when compared with the overall SCH population. Furthermore, the drug demonstrated efficacy when used in either the short- or long-term, although the effect was greater in studies with a treatment duration of duration no longer than 6 months.
SCH occurs when serum thyroid-stimulating hormone (TSH) levels are elevated while serum free thyroxine (FT4) remains at normal levels. Affected patients frequently present with lipid abnormalities, especially elevated TC and LDL cholesterol levels. The control of cholesterol, an independent risk factor of coronary heart disease (CHD), may therefore benefit SCH patients. [J Clin Endocrinol Metab 2015;100:1887-1894; JAMA 2010;304:1365-1374]
The present data reveal that levothyroxine treatment yields substantial reductions in TC and LDL cholesterol in SCH patients, including those with only mild SCH. Still, further studies are warranted to investigate the optimal way to employ this treatment in practice and to shed light on the underlying mechanism for attenuating efficiency during long-term treatment, researchers said.