Low Thyroid Function Linked to Greater Type 2 Diabetes Risk

Miriam E Tucker

April 11, 2016

BOSTON — Low and low-normal thyroid function are associated with an increased risk for type 2 diabetes, new research suggests.

The findings, from a large population-based cohort in the Netherlands, were presented April 3 here at the annual meeting of the Endocrine Society, ENDO 2016, by Layal Chaker, MD, of Erasmus Medical Center, Rotterdam, the Netherlands.

"Low thyroid function is associated with a higher risk of developing diabetes and also of progression from prediabetes to diabetes," Dr Chaker said during a press briefing, adding that this risk is also evident even among those in the low-normal range of thyroid function.

Asked to comment, briefing moderator Margaret Eckert-Norton, PhD, of St Joseph's College and the State University of New York, Downstate, Brooklyn, told Medscape Medical News, "Of course, we've always screened for thyroid disorders in patients with type 1 diabetes, because of the autoimmune association.…But there's overlap between the symptoms of hypothyroidism and type 2 diabetes."

Dr Eckert-Norton added, "This gives us something to bring to our insurance companies.…I think it makes the case for screening."

The study received an "Outstanding Abstract Award" at the conference.

Even in Normal Range, Low Thyroid Function Predicts Diabetes

The study included 8452 Rotterdam residents aged 45 and older without diabetes at baseline. They had a mean age of 65 years and mean body mass index (BMI) of 26.5 kg/m2, and 58% were female.

They had an average thyroid-stimulating hormone (TSH) level of 1.91 mIU/L and free thyroxine of 15.7 pmol/L, both within the expected range.

During a mean follow-up of 7.9 years, 1100 subjects developed prediabetes and 798 developed type 2 diabetes.

After adjustment for sex, age, smoking, fasting serum glucose, and cohort, those in the highest tertile for TSH had a significant 1.13 times increased risk of developing type 2 diabetes compared with the lowest tertile. When limited to the 85% of subjects within the normal TSH range, there was a significant 1.24-fold elevated risk for the highest vs lowest tertile.

Higher free T4 was associated with a lower diabetes risk, with a hazard ratio of 0.96 for both the full range of measurements and those within the normal thyroid-function range.

The risk of progression from prediabetes (fasting glucose 106-126 mg/dL) to type 2 diabetes (>126 mg/dL) was 1.25-fold higher comparing the lowest to the highest tertiles of TSH and 1.39 for those within the normal range (P = .002).

Free T4 again showed the inverse relationship, with hazard ratios of 0.92 and 0.90 for the highest vs lowest tertiles in the full and normal ranges of thyroid-function measurements, respectively.

In absolute terms, the risk for type 2 diabetes increased from 19% to 35% as TSH rose from 0.4 to 4.0 mIU/L, while the diabetes risk dropped from 35% to 15% as free T4 increased from 11 to 25 pmol/L.

Asked by Medscape Medical News during the briefing what the mechanism for the association might be, Dr Chaker said that this isn't really known, but that thyroid hormone is important for energy expenditure and weight, so the effect might be mediated by BMI and other metabolic-syndrome components or perhaps a direct effect on beta-cell function.

"It deserves further research," she said.

Dr Eckert-Norton commented, "This is, I think, a very strong piece of work. I really look forward to seeing if this is [also] true with our African-American, Latino, and Asian populations."

The study authors and Dr Eckert-Norton have no relevant financial relationships.

ENDO 2016; April 3, 2016; Boston, Massachusetts. Abstract OR33-2

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