Subclinical hypothyroidism is a risk factor for nephropathy and cardiovascular diseases in Type 2 diabetic patients.

AIMS: The purpose of this study was to determine the relationship between subclinical hypothyroidism and prevalence of retinopathy and nephropathy, incident cardiovascular disease, and mortality in Type 2 diabetic patients without taking thyroid medication.

METHODS: Serum thyrotropin and free thyroxine concentrations were measured in 588 Type 2 diabetic subjects in Taipei Veterans General Hospital, Taiwan. In a cross-sectional study, we examined the prevalence of retinopathy and nephropathy. In a longitudinal study, we examined the risk of cardiovascular disease events, cardiovascular mortality and total mortality in the 4-year follow-up.

RESULTS: In the cross-sectional analysis, subclinical hypothyroidism was associated with a greater prevalence of diabetic nephropathy (odds ratio, 3.15 [95% CI, 1.48-6.69]) and did not show a high prevalence of diabetic retinopathy (odds ratio, 1.15 [95% CI, 0.59-2.26]) compare to euthyroid diabetics. During the 44.0 +/- 7.4 months of follow-up, 51 participants had cardiovascular events. The risk of cardiovascular events was significantly increased in Type 2 diabetics with subclinical hypothyroidism after adjustment for age, sex, A1C, other standard cardiovascular risk factors and medication (hazard ratio, 2.93; 95% CI, 1.15-7.48; P = 0.024), but it became nonsignificant after additional adjustment for urinary albumin-to-creatinine ratio (hazard ratio, 2.06; 95% CI, 0.67-6.36; P = 0.211). The rates of cardiovascular-related and total mortality did not significantly differ by thyroid status.

CONCLUSIONS: Type 2 diabetic patients with subclinical hypothyroidism are associated with an increased risk of nephropathy and cardiovascular events, but not with retinopathy. Our data suggest that the higher cardiovascular events in subclinical hypothyroidism with Type 2 diabetes may be mediated with nephropathy.