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Low Thyroid Function and Type 2 Diabetes

Study finds hypothyroidism tied to type 2 diabetes.

Having too little thyroid hormone in the blood–even in the low-normal range–raises the risk of developing type 2 diabetes, especially in people with prediabetes, a new study in nearly 8,500 people finds. Adults in the lowest third of thyroid function levels had a 1.4 time higher risk of progressing from prediabetes to type 2 diabetes than those in the highest third of thyroid function, according to a study presented at the Endocrine Society annual meeting. Dutch researchers used a cohort of adults without diabetes at baseline, ages 45 and older, and found those with higher thyroid-stimulating hormone had a 1.2-fold increased risk of developing diabetes.

Patients diagnosed with prediabetes have a 40% greater likelihood of developing diabetes if they are also diagnosed with hypothyroidism.

Layal Chaker, MD, of Erasmus Medical Center in Rotterdam, Netherlands, in his presentation, added that, “Low thyroid function is associated with higher risk of developing diabetes, but also the progression from prediabetes to diabetes and this is even within the normal range of thyroid function, “Low thyroid function as represented by higher TSH [thyroid-stimulating hormone] is with a 1.2-fold increased risk of diabetes and a 1.4-fold increased risk for progression from prediabetes.”

She added that, over a lifetime, 70% to 75% of people diagnosed with prediabetes will progress to diabetes. Dr. Chaker presented the results at ENDO 2016.

Thyroid hormone is important for metabolism, and thus important in controlling weight and cholesterol metabolism. Therefore, Dr Chaker and her team hypothesized that thyroid hormone could also be important in the development of type 2 diabetes.

To test their hypothesis, the research team evaluated thyroid function, incidence of diabetes, and progression from prediabetes to diabetes. Dr. Chaker and colleagues selected 8,452 participants from the Rotterdam Study, a population-based study of adults aged 45 or older that reflects the general population in the Netherlands. The study population was 58% women and average age was 65 years. On average, TSH and free thyroxine (FT4) were on par with that of the general population (1.91 mIU/L and 1.22 ng/dL, respectively).

No patient had diabetes at baseline. All participants were tested for blood sugar and thyroid function, and re-examined every 2 to 3 years to check for the development of type 2 diabetes.

Patients with fasting glucose between 108 mg /dL and 125 mg/dL. (6 mmol/L and 7 mmol/L) were considered to have prediabetes, and those with a fasting glucose of 125 mgm/dL.(7 mmol/L) or above were considered to have diabetes.

Over an average follow-up of nearly eight years, 1,100 participants developed prediabetes and 798 developed diabetes. Higher TSH was linked to increased diabetes risk (hazard ratio [HR]=1.13; 95% CI, 1.08-1.18 per log TSH), even within the reference range of thyroid function (HR=1.24; 95% CI, 1.06-1.45).

Risk for progression from prediabetes to diabetes was 1.4 times greater for participants in the lowest third of thyroid function levels compared with those in the highest third (P=.002).

The researchers found it surprising that even people whose thyroid function was in the low-normal range had an increased risk of diabetes. From the results, the researchers suggested that we should consider screening people with prediabetes for low thyroid function.

They also learned that hypothyroidism is associated with increased risk for diabetes and subclinical hypothyroidism appears to increase this risk only with statin use, according to research published in Diabetes Care.

Naomi Gronich, MD, from the Israel Institute of Technology in Haifa, and colleagues examined risk factors for the development of statin-associated diabetes in a two-phase study. Risk factors were identified in a high-throughput in silico processing phase.

In the second phase, the most prominent risk factor identified was confirmed in an observational cohort study at the largest healthcare organization in Israel. Overall, 39,263 statin nonusers were propensity score matched with 20,334 highly compliant statin initiators in 2004 to 2005; patients were followed through 2010.

In a multivariable model, hypothyroidism and subclinical hypothyroidism correlated with increased risk for diabetes (rate ratios, 1.53 and 1.75, respectively) among statin users and nonusers, according to the researchers. The correlation between hypothyroidism and increased diabetes risk was seen for statin users and nonusers, regardless of statin use (rate ratios, 2.06 and 1.66, respectively).

Subclinical hypothyroidism also correlated with increased diabetes risk only for statin users (rate ratios, 1.94; 95% CI, 1.13-3.34] for statin users and 1.2 95% CI, 0.52 -2.75 for nonusers).

There was no increased diabetes risk for patients with hypothyroidism treated with thyroid hormone replacement therapy.

The researchers wrote, “Hypothyroidism is a risk factor for [diabetes]…Subclinical hypothyroidism-associated risk for [diabetes] is prominent only upon statin use.”

Practice Pearls:

  • Study finds hypothyroidism tied to type 2 diabetes.
  • Risk for progression from prediabetes to diabetes was 1.4 times greater for participants in the lowest third of thyroid function levels compared with those in the highest third.
  • The correlation between hypothyroidism and increased diabetes risk was seen for statin users and nonusers, regardless of statin use.

Researched and prepared by Steve Freed, BPHarm, Diabetes Educator, Publisher and reviewed by Dave Joffe, BSPharm, CDE
Chaker L, Ligthart, Korevaar TIM, et al. OR33-2: Thyroid Function and type 2 diabetes risk: a population-based prospective cohort study. Presented at: ENDO 2016; April 1-4, 2016; Boston, MA.  Gronich N et al. Diabetes Care. 2015;doi:10.2337/dc14-2515.