Thyroid function and risk of type 2 diabetes: a population-based prospective cohort study.
BACKGROUND
The association of thyroid function with risk of type 2 diabetes remains elusive. We aimed to investigate the association of thyroid function with incident diabetes and progression from prediabetes to diabetes in a population-based prospective cohort study.


METHODS
We included 8452 participants (mean age 65 years) with thyroid function measurement, defined by thyroid-stimulating hormone (TSH) and free thyroxine (FT4), and longitudinal assessment of diabetes incidence. Cox-models were used to investigate the association of TSH and FT4 with diabetes and progression from prediabetes to diabetes. Multivariable models were adjusted for age, sex, high-density lipoprotein cholesterol, and glucose at baseline, amongst others.


RESULTS
During a mean follow-up of 7.9 years, 798 diabetes cases occurred. Higher TSH levels were associated with a higher diabetes risk (hazard ratio [HR] 1.13; 95 % confidence interval [CI], 1.08-1.18, per logTSH), even within the reference range of thyroid function (HR 1.24; 95 % CI, 1.06-1.45). Higher FT4 levels were associated with a lower diabetes risk amongst all participants (HR 0.96; 95 % CI, 0.93-0.99, per 1 pmol/L) and in participants within the reference range of thyroid function (HR 0.96; 95 % CI, 0.92-0.99). The risk of progression from prediabetes to diabetes was higher with low-normal thyroid function (HR 1.32; 95 % CI, 1.06-1.64 for TSH and HR 0.91; 95 % CI, 0.86-0.97 for FT4). Absolute risk of developing diabetes type 2 in participants with prediabetes decreased from 35 % to almost 15 % with higher FT4 levels within the normal range.


CONCLUSIONS
Low and low-normal thyroid function are risk factors for incident diabetes, especially in individuals with prediabetes. Future studies should investigate whether screening for and treatment of (subclinical) hypothyroidism is beneficial in subjects at risk of developing diabetes.
Rotterdam Thyroid Center, Erasmus University Medical Center, Rotterdam, The Netherlands.|Department of Internal Medicine, Erasmus University Medical Center, Rotterdam, The Netherlands.|Department of Epidemiology, Erasmus University Medical Center, Room NA-2828, 3000CA, Rotterdam, The Netherlands.
Layal
L
Chaker
Department of Epidemiology, Erasmus University Medical Center, Room NA-2828, 3000CA, Rotterdam, The Netherlands.
Symen
S
Ligthart
Rotterdam Thyroid Center, Erasmus University Medical Center, Rotterdam, The Netherlands.|Department of Internal Medicine, Erasmus University Medical Center, Rotterdam, The Netherlands.|Department of Epidemiology, Erasmus University Medical Center, Room NA-2828, 3000CA, Rotterdam, The Netherlands.
Tim I M
TI
Korevaar
Department of Epidemiology, Erasmus University Medical Center, Room NA-2828, 3000CA, Rotterdam, The Netherlands.|Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA.
Albert
A
Hofman
Department of Epidemiology, Erasmus University Medical Center, Room NA-2828, 3000CA, Rotterdam, The Netherlands.
Oscar H
OH
Franco
Rotterdam Thyroid Center, Erasmus University Medical Center, Rotterdam, The Netherlands. r.peeters@erasmusmc.nl.|Department of Internal Medicine, Erasmus University Medical Center, Rotterdam, The Netherlands. r.peeters@erasmusmc.nl.|Department of Epidemiology, Erasmus University Medical Center, Room NA-2828, 3000CA, Rotterdam, The Netherlands. r.peeters@erasmusmc.nl.
Robin P
RP
Peeters
Department of Epidemiology, Erasmus University Medical Center, Room NA-2828, 3000CA, Rotterdam, The Netherlands.
Abbas
A
Dehghan
Diabetes; Prediabetes; Thyroid function; Thyroid hormone; Type 2 diabetes
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