The relationship between thyroid stimulating hormone within the reference range and coronary artery disease: impact of age.

Studies on the relationship between thyroid stimulating hormone (TSH) within the reference range and coronary artery disease (CAD) have produced conflicting results. Furthermore, the effect of age on this relationship has never been explored. The aim of this study was to investigate the association between TSH levels and CAD among euthyroid subjects and whether age influenced this relationship. A total of 318 subjects who underwent coronary angiography were included. Serum TSH, T3, T4, lipid, blood glucose and creatinine levels were measured and compared between the groups with and without CAD. Age-stratified analysis and multivariate logistic regression analysis were performed. Levels of TSH, T3 and T4 did not differ significantly between CAD (n=196) and non-CAD group (n=122) (TSH: 1.77 ± 0.99 vs 1.89 ± 0.98 mIU/L, T3: 1.45 ± 0.36 vs 1.51 ± 0.35 nmol/L, T4: 100.06 ± 20.49 vs 103.95 ± 24.06 nmol/L, respectively) when comparisons were performed among all subjects. A significant between-group difference in levels of TSH was observed among subjects less than or equal to 65 years old (CAD group: n=121, non-CAD group: n=106), with higher TSH levels in CAD group (2.03 ± 0.94 vs 1.75 ± 0.97 mIU/L, adjusted p=0.024). Multivariate logistic regression analysis revealed that elevated level of TSH was an independent predictor for CAD (odds ratio: 1.512, p=0.011). No significant between-group difference in TSH levels was observed among subjects older than 65 years (CAD group: n=75, non-CAD group: n=16). The results showed that higher levels of TSH within the reference range were independently associated with the presence of CAD only among subjects less than or equal to 65 years old, suggesting age might influence the relationship.