The hyperthyroid state is associated with prevalent and incident type 2 diabetes mellitus in two population-based studies

 

Background and Aims:

A potential causal relationship between thyroid function and type 2 diabetes mellitus is currently under debate, but the current state of research is limited. Our aim was to investigate the association of thyroid hormone levels with prevalent and incident type 2 diabetes mellitus (T2DM) in two representative studies.

Methods:

Analyses are based on data from the Study of Health in Pomerania (SHIP), a German population-based cohort with 4,308 individuals at baseline and 3,300 individuals at a five-year follow-up, and from INTER99, a Danish population-based randomized controlled trial with 6,784 individuals at baseline and 4,516 individuals at the five-year-follow-up. Serum thyroid-stimulating hormone (TSH) and free thyroxine (fT4) concentrations were measured in both studies. T2DM was defined by self-report or intake of anti-diabetic medication. Individuals with T2DM were defined as controlled if they had a HbA1c < 7.5% (58 mmol/mol).

Results:

Neither in SHIP nor in INTER99 we detected significant associations of serum TSH levels with prevalent T2DM. Serum fT4 levels were significantly positively associated with prevalent T2DM in SHIP and INTER99. In longitudinal analyses baseline levels of fT4 were significantly positively associated with incident T2DM in SHIP (RR = 1.07; 95%-CI = 1.04 – 1.10), while this association barely missed statistical significance in INTER99 (RR = 1.03; 95%-CI = 0.99 – 1.07). In both studies serum fT4 levels were significantly associated with incident controlled T2DM.

Conclusion:

We demonstrated positive associations of thyroid hormones with prevalent and incident T2DM suggesting that the hyperthyroid state may contribute to the pathogenesis of this condition.