Diabetes linked to hypothyroidism risk

Patients with Type 2 diabetes are at an increased risk for hypothyroidism, especially if they are aged 65 years or older, research shows.

The study also showed that diabetic macroangiopathy and metformin treatment might be predictors for unidentified hypothyroidism in this population.

“Recent retrospective and prospective surveys have shown that Type 2 diabetes patients have a remarkably high prevalence of unidentified thyroid disease,” say J. Díez and P. Iglesias (Hospital Ramón y Cajal, Madrid, Spain).

The authors previously found that among 318 patients with diabetes, the overall prevalence of hypothyroidism and newly diagnosed hypothyroidism was 25.8% and 8.2%, respectively. “However, we could not find any diabetes-related variables with the predictive capacity for the presence of thyroid dysfunction,” they explain.

The team therefore analyzed the relative risk for hypothyroidism in a larger cohort of diabetes patients who underwent a screening program for hypothyroidism during 2004–2010. The study included 1112 individuals, aged a median of 66.7 years, with a median diabetes duration of 10 years. A previous history of thyroid dysfunction was present/reported in 179 patients (136 with hypothyroidism and 43 with hyperthyroidism).

A control group comprising 911 individuals without known diabetes or thyroid disease was also evaluated.

As reported in Diabetic Medicine, 204 of the participants were found to have hypothyroidism; there were 110 cases of overt thyroid hypothyroidism (thyroid stimulating hormone [TSH] >5 mU/L and free thyroxine [T4] <9 pmol/L) and 94 cases of subclinical thyroid hypothyroidism (TSH >5 mU/L and normal T4).

In patients without previous thyroid dysfunction, four were found to have overt hypothyroidism and 64 subclinical hypothyroidism.

Overall, diabetes patients were at a significantly increased risk for hypothyroidism compared with control individuals, at a gender-, age-, and weight-adjusted odds ratio (OR) of 2.81.

The increased hypothyroidism risk was significant in both women and men, patients over 65 years of age, obese and nonobese patients, and patients with and without thyroid autoimmunity. In individuals without thyroid antibodies, the increased risk was significant in men and in patients over 65 years of age.

Logistic regression analysis revealed that among those without a history of thyroid disease, incident hypothyroidism was significantly associated with the presence of macroangiopathy, metformin treatment, and thyroid autoimmunity, at ORs of 2.85, 2.51, and 19.15, respectively.

“To our knowledge this is the first study that demonstrates an increase in the risk for undiagnosed hypothyroidism in patients with Type 2 diabetes,” write Díez and Iglesias.

The researchers say their results “have clinical implications because of the high prevalence of hypothyroidism in patients with diabetes and because unrecognized thyroid hypofunction may increase the existing cardiovascular risk in patients with Type 2 diabetes.”

The data favor detection of hypothyroidism in patients with Type 2 diabetes, particularly in those older than 65 years, they conclude.

Reference: Diabet Med 2012; Advance online publication