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Effects of 18 months of l ‐T4 replacement in women with subclinical hypothyroidism
Author(s) -
Adrees M.,
Gibney J.,
ElSaeity N.,
Boran G.
Publication year - 2009
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.2008.03509.x
Subject(s) - medicine , cystatin c , endocrinology , renal function , homocysteine , brachial artery , context (archaeology) , blood pressure , endothelial dysfunction , subclinical infection , triglyceride , lipoprotein , lipoprotein(a) , cholesterol , biology , paleontology
Summary Context Some of the cardiovascular and renal abnormalities seen in overt hypothyroidism have also been reported in subclinical hypothyroidism (SCH). Short‐term l ‐T4 replacement in SCH improves cardiovascular risk markers and reduces carotid intima‐media thickness (CIMT), a surrogate marker of atherosclerosis. The haemodynamic and renal effects of l ‐T4 replacement in SCH are poorly understood. Objectives To compare cardiovascular risk factors and renal variables in women with SCH and normal women. To study the effects of l ‐T4 replacement in SCH subjects on these variables and on structural and functional changes in common carotid and brachial arteries. Design Fifty‐six women with SCH before and after l ‐T4 replacement for 18 months and 56 normal women of similar age distribution were studied. Blood Pressure (BP), plasma lipids and homocysteine were measured and renal function evaluated [estimation of glomerular filtration rate (eGFR) using standard equations and measurement of serum Cystatin‐C] in women with SCH before and after 18 months of l ‐T4, and in healthy women. CIMT and endothelial function (using brachial artery ultrasound) were studied before and after l‐ T4 in a subgroup of women with SCH. Results Systolic and diastolic BP, total cholesterol, triglyceride, LDL‐cholesterol, lipoprotein(a) and homocysteine were greater in SCH ( P < 0·05), and following l‐ T4 replacement decreased ( P < 0·05) to levels that no longer differed from normal subjects. Estimated GFR was reduced and serum Cystatin‐C increased ( P < 0·05) in SCH. These variables also normalized following l ‐T4. Following l ‐T4 replacement the carotid artery baseline diameter increased by 7·1% and CIMT decreased by a mean value of 13%, while brachial artery diameter increased basally by 12·5% and following endothelium‐dependent vasodilatation by 17·5% ( P < 0·05). However, the increment following reactive hyperaemia did not differ before or following l‐ T4 replacement. Conclusion Normalization of cardiovascular risk factors following l‐ T4 replacement in SCH potentially explains reduced CIMT. Increased carotid and brachial artery diameters and normalized eGFR indicates a haemodynamic effect of l‐ T4 replacement, the importance of which requires further investigation.