Type 2 Diabetes Risk Increased With Low Thyroid Function

BOSTON — Patients diagnosed with prediabetes have a 40% greater likelihood of developing diabetes if they are also diagnosed with hypothyroidism.

“Low thyroid function is associated with higher risk of developing diabetes, but also the progression from prediabetes to diabetes and this is even within the normal range of thyroid function,” said Layal Chaker, MD, of Erasmus Medical Center in Rotterdam, Netherlands.“Low thyroid function as represented by higher TSH [thyroid-stimulating hormone] is associated with a 1.2-fold increased risk of diabetes and a 1.4-fold increased risk for progression from prediabetes.”

She added that, over a lifetime, 70% to 75% of people diagnosed with prediabetes will progress to diabetes.

Dr Chaker presented the results at ENDO 2016.

Thyroid hormone is important for metabolism, and thus important in controlling weight and cholesterol metabolism. Therefore, Dr Chaker and her team hypothesized that thyroid hormone could also be important in the development of type 2 diabetes.

To test their hypothesis, the research team evaluated thyroid function, incidence of diabetes, and progression from prediabetes to diabetes. Dr Chaker and colleagues selected 8452 participants from the Rotterdam Study, a population-based study of adults aged 45 or older that reflects the general population in the Netherlands. The study population was 58% women and average age was 65 years. On average, TSH and free thyroxine (FT4) were on par with that of the general population (1.91 mIU/L and 1.22 ng/dL, respectively).

No patient had diabetes at baseline. All participants were tested for blood sugar and thyroid function, and reexamined every 2 to 3 years to check for the development of type 2 diabetes.

Patients with fasting glucose between 6 mmol/L and 7 mmol/L were considered to have prediabetes, and those with a fasting glucose of 7 mmol/L or above were considered to have diabetes.

Over an average follow-up of nearly 8 years, 1100 participants developed prediabetes and 798 developed diabetes. Higher TSH was linked to increased diabetes risk (hazard ratio [HR]=1.13; 95% CI, 1.08-1.18 per log TSH), even within the reference range of thyroid function (HR=1.24; 95% CI, 1.06-1.45).

Additionally, diabetes risk was lower with higher FT4 levels in all (HR=0.96; 95% CI, 0.93-0.99 per pmol/L) and in those within the reference range (HR=0.96; 95% CI, 0.92-0.99).

Risk for progression from prediabetes to diabetes was 1.4 times greater for participants in the lowest third of thyroid function levels compared with those in the highest third (P=.002).

“We found it surprising that even people whose thyroid function was in the low-normal range had an increased risk of diabetes,” Dr Chaker said. “These findings suggest we should consider screening people with prediabetes for low thyroid function.”

Reference

1. Chaker L, Ligthart, Korevaar TIM, et al. OR33-2: Thyroid Function and type 2 diabetes risk: a population-based prospective cohort study. Presented at: ENDO 2016; April 1-4, 2016; Boston, MA.