In the JournalsPerspective

Thyroid hormones related to type 2 diabetes prevalence in adults

The prevalence of type 2 diabetes in adults is independently related to decreased free triiodothyronine and free triiodothyronine-to-free thyroxine ratio, and increased free thyroxine concentrations, study data show.

Kaijun Niu, MD, PhD, of the Nutritional Epidemiology Institute and School of Public Health at Tianjin Medical University in China, and colleagues evaluated data from the TCLSIHealth cohort study 2013-2015 on 15,296 adults (8,970 men) to determine whether thyroid hormone levels within the reference range are related to type 2 diabetes.

Overall, the prevalence of type 2 diabetes among participants was higher in men (16.2%) than women (7.7%). Compared with women, men had higher free T3 and free T4 levels (P < .0001 for both). However, thyroid-stimulating hormone levels were lower in men compared with women (P < .0001).

Compared with participants without diabetes, those with diabetes were older; had higher BMI, waist circumference, total cholesterol, triglycerides, and systolic and diastolic blood pressure; were more likely to have a family history of hyperlipidemia and diabetes; and had lower HDL levels (P < .01 for all). Men with diabetes had lower free T3 levels and free T3/free T4 ratio and higher free T4 levels compared with men without diabetes (P < .05 for all). Compared with women without diabetes, women with diabetes had higher LDL and free T4 levels and lower free T3/free T4 ratios (P < .01 for all).

Among men, gradual increases in free T3, free T3/free T4 ratios and TSH concentrations were related to the adjusted ORs of type 2 diabetes compared with men with the lowest concentrations of thyroid hormones.

“Decreased [free] T3, [free] T3/[free] T4 ratios and increased [free] T4 levels were independently related to the prevalence of [type 2 diabetes] among the adult population,” the researchers wrote. “[A] significantly negative relationship between TSH and [type 2 diabetes] was observed in males, but not in females. Future studies should be aimed at clarifying cause and effect relationship between [thyroid hormones] and [type 2 diabetes].” – by Amber Cox

Disclosure: The researchers report no relevant financial disclosures.

The prevalence of type 2 diabetes in adults is independently related to decreased free triiodothyronine and free triiodothyronine-to-free thyroxine ratio, and increased free thyroxine concentrations, study data show.

Kaijun Niu, MD, PhD, of the Nutritional Epidemiology Institute and School of Public Health at Tianjin Medical University in China, and colleagues evaluated data from the TCLSIHealth cohort study 2013-2015 on 15,296 adults (8,970 men) to determine whether thyroid hormone levels within the reference range are related to type 2 diabetes.

Overall, the prevalence of type 2 diabetes among participants was higher in men (16.2%) than women (7.7%). Compared with women, men had higher free T3 and free T4 levels (P < .0001 for both). However, thyroid-stimulating hormone levels were lower in men compared with women (P < .0001).

Compared with participants without diabetes, those with diabetes were older; had higher BMI, waist circumference, total cholesterol, triglycerides, and systolic and diastolic blood pressure; were more likely to have a family history of hyperlipidemia and diabetes; and had lower HDL levels (P < .01 for all). Men with diabetes had lower free T3 levels and free T3/free T4 ratio and higher free T4 levels compared with men without diabetes (P < .05 for all). Compared with women without diabetes, women with diabetes had higher LDL and free T4 levels and lower free T3/free T4 ratios (P < .01 for all).

Among men, gradual increases in free T3, free T3/free T4 ratios and TSH concentrations were related to the adjusted ORs of type 2 diabetes compared with men with the lowest concentrations of thyroid hormones.

“Decreased [free] T3, [free] T3/[free] T4 ratios and increased [free] T4 levels were independently related to the prevalence of [type 2 diabetes] among the adult population,” the researchers wrote. “[A] significantly negative relationship between TSH and [type 2 diabetes] was observed in males, but not in females. Future studies should be aimed at clarifying cause and effect relationship between [thyroid hormones] and [type 2 diabetes].” – by Amber Cox

Disclosure: The researchers report no relevant financial disclosures.

    Perspective

    PERSPECTIVE

    Layal Chaker

    The paper by Gu and colleagues is not the first study to report the link between thyroid function and type 2 diabetes in euthyroid individuals in the general population. Our group has recently published a study showing an up to 20% increase in the absolute risk of developing type 2 diabetes in euthyroid participants with lower free thyroxine and higher thyroid-stimulating hormone levels (Chaker L, et al. BMC Med. 2016;doi:10.1186/s12916-016-0693-4). Jun and colleagues also recently published a study with similar results, ie, a positive association of low-normal thyroid function with type 2 diabetes (Jun JE, et al. Thyroid. 2016;doi:10.1089/thy.2016.0171). Nevertheless, the study by Gu and colleagues is yet another study adding to the evidence that low-normal thyroid function could be a risk factor for type 2 diabetes, even though their results on free thyroxine levels are somewhat controversial.
    However, it is still unclear what the implications are for clinical practice. Treatment is not indicated and might even be harmful. After all, recent studies have also shown that high-normal thyroid function is associated with adverse clinical events, including sudden cardiac death and dementia. Therefore, it would be difficult to determine at which value treatment should be initiated. Importantly, there is also no evidence that thyroid hormone treatment decreases the risk for developing type 2 diabetes. Further studies are needed to answer these open questions. Without this evidence, treatment is not indicated and even discouraged in such a large number of individuals in the general population.


    Layal Chaker, MD, MSc
    Research and Curriculum Fellow, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA; Research Fellow, Department of Endocrinology and Epidemiology, Erasmus Medical Center, Rotterdam, Netherlands

    Disclosure:Chaker reports no relevant financial disclosures.