A new study for which the results are going to be presented at the Endocrine Society's 98th annual meeting in Boston concludes that having too little thyroid hormone in the blood--even in the low-normal range--raises the risk of developing Type 2 diabetes, especially in people with prediabetes.

In this study, it was observed that the risk of developing type 2 diabetes over long-term follow-up increased by 13 percent for people with low thyroid function--often called hypothyroidism--or even those with low-normal thyroid function. However, the diabetes risk was up to 40 percent higher for individuals with reduced thyroid function if they already had prediabetes, the investigators reported. The study by lead investigator Layal Chaker, MD, of Erasmus Medical Center, Rotterdam, the Netherlands and her colleagues included 8,452 participants from the Rotterdam Study, a population-based study in adults age 45 or older that reflects the general population in the Netherlands. Participants had an average age of 65 years. All participants had blood tests to measure their blood sugar and thyroid function. They were reexamined every two or three years to check for the development of Type 2 diabetes, and their medical records also were reviewed.

Over an average follow-up of nearly eight years, 1,100 participants developed prediabetes and 798 developed diabetes. The researchers found that even among participants whose thyroid function was in the normal range at first measurement, progression from prediabetes to diabetes was reportedly 1.4 times higher for those in the lowest third of thyroid function levels compared with the highest third. "We found it surprising that even people whose thyroid function was in the low-normal range had an increased risk of diabetes. These findings suggest we should consider screening people with prediabetes for low thyroid function," Chaker said.

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