Interactions among thyroid function, insulin sensitivity, and serum lipid concentrations: the Fremantle diabetes study.
BACKGROUND
Recent observations in healthy subjects showed that insulin resistance modifies the relationship between serum cholesterol and thyroid function.


OBJECTIVE
The aim of the study was to determine whether insulin sensitivity modifies the association between thyroid dysfunction and lipid parameters in diabetic patients.


METHODS
This is a cross-sectional study.


METHODS
This is a community-based observational study.


METHODS
One hundred seventeen females with type 2 diabetes who were not taking oral hypoglycemic therapy, insulin, or lipid-lowering therapy participated in the study.


METHODS
Serum TSH, insulin, total and high-density lipoprotein cholesterol, and triglycerides were measured.


METHODS
Age-adjusted multiple linear regression analysis of serum lipid concentrations and derived parameters, as functions of serum TSH and homeostasis model assessment-derived insulin sensitivity (HOMA-S), were measured.


RESULTS
The relationship among serum lipid concentrations, serum TSH, and HOMA-S was significantly modified by an interaction term ln(TSH)*ln(HOMA-S). In three-dimensional graphs, there were strong positive associations between TSH and lipid parameters with adverse cardiac risks at low insulin sensitivity that were absent at higher insulin sensitivity. The effect was strongest for lipid risk factors associated with insulin resistance.


CONCLUSIONS
The interaction between thyroid function and insulin sensitivity is an important contributor to diabetic dyslipidemia and may justify T4 replacement in some patients.
Chubb
S A P
SA
Department of Biochemistry, Fremantle Hospital, P.O. Box 480, Fremantle, Western Australia 6959, Australia. paul.chubb@health.wa.gov.au
Davis
W A
WA
Davis
T M E
TM
D000368:Aged; D003430:Cross-Sectional Studies; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000503:physiopathology*; D005260:Female; D006706:Homeostasis; D006801:Humans; D007333:Insulin Resistance; D016014:Linear Models; D008055:Lipids / Q000097:blood*; D008875:Middle Aged; D009994:Osmolar Concentration; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000503:physiopathology*; D013972:Thyrotropin / Q000097:blood
D008055:Lipids; D013972:Thyrotropin