The Relationship between Serum Cholesterol and Serum Thyrotropin, Thyroxine and Tri-Iodothyronine Concentrations in Suspected Hypothyroidism

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Abstract
The relationship between serum cholesterol, thyrotropin, thyroxine and tri-iodothyronine was investigated in 1018 female patients over 40 years of age with suspected hypothyroidism. The correlation between serum thyrotropin and cholesterol (r = 0.398) and between thyroxine and cholesterol (r = — 0·217) were both highly significant (P < 0·001), but the correlation between tri-iodothyronine and cholesterol (r = −0·011) was not significant. Only in patients with a serum thyrotropin in excess of 40 mU/L was there a clinically appreciable increase in the serum cholesterol. In 139 patients treated for hypothyroidism by thyroxine replacement there was a highly significant correlation (P < 0·001) between the decrease in serum thyrotropin and cholesterol (r = 0·593). The correlation between increase in serum thyroxine and decrease in cholesterol (r = — 0·401) was also highly significant (P < 0·001), but there was an even stronger correlation between the increase in serum tri-iodothyronine and the decrease in serum cholesterol (r = — 0·529).