Association between subclinical hypothyroidism and cardiovascular diseases in type 2 diabetic patients

Objective To assess the relationship between subclinical hypothyroidism and cardiovascular diseases in patients with type 2 diabetes. Methods A total of 123 type 2 diabetic patients with subclinical hypothyroidism (case group) and 266 type 2 diabetic patients with normal thyroid function (control group) were admitted from July 2013 to July 2014. The general information, as well as the level of plasma glucose, serum lipids, thyroid function, etc., were collected and compared. Tensors were stratified according to serum thyrotropin (TSH), free triiodothyronine (FT3) and free thyroxine (FT4). After adjusting for confounding factors, logistic regression analysis was used for analyzing the correlation among subclinical hypothyroidism, thyroid related indicators and cardiovascular disease. Results (1) In the case group, the proportion of male patients [41.46% (51/123) ], statins use [1.67% (2/123) ] and smoking [10.57% (13/123) ], level of glycated hemoglobin (HbA1c) (8.61%±0.18%) and FT4 [ (16.20±0.25) pmol/L] was significantly lower than that in the control group [60.15% (160/266) , 9.40% (25/266) , 24.06% (64/266) , 9.45%±0.12%, (16.85±0.14) pmol/L, t=-3.808-13.150, all P<0.05]. The level of TSH in the case group was significantly higher than that in the control group [4.9 (4.5-7.1) vs (1.8 (1.2-2.6) nU/L, t=-24.069, P<0.05]. (2) After adjusting multiple traditional cardiovascular risk factors, the risk of cardiovascular disease in case group was significantly increased compared to the control group (OR=3.205, 95%CI=1.219-8.425, P=0.018). The risk of cardiovascular disease was significantly increased in the third TSH tertile group compared to the first TSH tertile group [4.369 (1.462-13.046) , P=0.008]. The tertiles of FT3 and FT4 were not associated with the risk of cardiovascular disease [FT3: 0.806 (0.305-2.130) , P=0.663; 1.268 (0.481-3.347) , P=0.631; FT4: 0.462 (0.181-1.179) , P=0.106; 0.873 (0.349-2.185) , P=0.772]. Conclusion Subclinical hypothyroidism is associated with cardiovascular disease in type 2 diabetic patients independently, and it might increase the risk of cardiovascular disease of type 2 diabetic patients by improving the level of serum TSH. Key words: Diabetes mellitus, type 2; Cardiovascular diseases; Thyrotropin; Subclinical hypothyroidism