BOSTON – Results of a population-based study involving more than 8,000 adults from the Netherlands who were diabetes free at baseline has implicated low thyroid function with a 13% increased likelihood of developing type 2 diabetes, and up to 40% higher in individuals with prediabetes.

The heightened risk exists even for individuals with subclinical hypothyroidism, in whom thyroid-stimulating hormone (TSH) in the blood is still in the normal concentration range.

“These findings suggest we should consider screening people with prediabetes for low thyroid function,” Dr. Layal Chaker of Erasmus Medical Center, Rotterdam, the Netherlands, said at the annual meeting of the Endocrine Society.

Thyroid screening is recommended for patients with type 1 diabetes, since they are at increased risk of thyroid disease. An association between thyroid dysfunction in the form of hypothyroidism and type 2 diabetes has been surmised, since type 2 diabetes and hypothyroidism tend to be more prevalent in older adults, and since hypothyroidism has been linked with weight gain and reduced sensitivity to insulin.

To further study the link between thyroid function and diabetes, Dr. Chaker and her colleagues studied data from 8,452 participants aged 45 years and above (mean age 62 years, 58% female) from the Rotterdam Study, a prospective, longitudinal cohort study in the Ommoord district of Rotterdam that was undertaken to investigate the risk factors of cardiovascular, neurological, ophthalmologic, and endocrine diseases in the elderly. The cohort was considered representative of the general population in the Netherlands. All participants had blood tests to measure blood glucose, TSH, and free thyroxine (FT4). Normal blood glucose was considered to be under 5.9 mmol/L, prediabetes as over 5.9 to less than 7.0 mmol/L glucose, and diabetes as above 7.0 mmol/L.

Prediabetes and type 2 diabetes developed in 1,100 and 798 subjects, respectively, during a mean follow-up of 7.9 years. Higher TSH levels increased the risk of development of type 2 diabetes risk (hazard ratio [HR] 1.13, 95% confidence interval [CI], 1.08-1.18, per logTSH). This risk held even for subjects whose TSH levels were at the lower end of the reference range of thyroid function (HR 1.24, CI, 1.06-1.45). The risk of diabetes was reduced in subjects with FT4 levels that were elevated (HR 0.96, CI, 0.93-0.99, per pmol/L) and for those whose FT4 levels were in the reference range (HR 0.96, CI, 0.92-0.99). Low thyroid function, even within the normal range, was associated with a 1.4 times risk of progression from prediabetes to type 2 diabetes (P = .002).

“Low and, surprisingly, low-normal thyroid function are risk factors for incident diabetes, especially in individuals with prediabetes,” said Dr. Chaker.

The data point to the need to clarify whether screening for and treatment of subclinical hypothyroidism can help curb the development of diabetes, she added.

Dr. Chaker had no disclosures.

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