Thyroid Dysfunction an Underestimated Comorbidity in Patients with Type 2 Diabetes

A new study suggests HCPs test for thyroid imbalances every two years

With Paul Chubb MD

Though patients with thyroid disorders are screened for diabetes, type 2 diabetics are not regularly tested for thyroid imbalances.

Patients with diabetes are prone to many co-morbidities – from heart disease to vision loss, from circulatory problems to gum disease. But there has not been consensus on how often those with diabetes also have problems with thyroid dysfunction.

There have been multiple studies showing a relationship between thyroid disorders and diabetes. Among the findings are studies showing:

  • glucose abnormalities, as an excess of thyroid hormone can result in increased glucose gut absorption
  •  Graves’ disease patients often have higher proinsulin levels
  • hypothyroidism is associated with metabolic syndrome and might be indirectly related to the onset of diabetes

But while those studies look at the incidence of diabetes among thyroid patients, a new study published in April views it from the other side: the incidence and prevalence of thyroid problems among those with diabetes.

Study results

The observational study involved more than 1,600 patients in a community setting in Australia. Of that patient cohort, 8% had been diagnosed with type 1 diabetes, 87.1% with type 2 diabetes, and 4.9% with latent autoimmune diabetes of adults (LADA). The study authors looked at the thyroid stimulating hormone (TSH) levels and free thyroxine levels of the patients over a four-year period.

Among the findings:

  • Prevalence, based on those who self-reported thyroid medication use or hospitalization data, was 11.7%
  • In a further 5.1%, there was evidence of subclinical hypothyroidism
  • Just over 1% had overt hypothyroidism
  • 0.3% had subclinical or overt hyperthyroidism
  • The total baseline prevalence was just under 17.5%

During follow-up over four years, the authors found:

  • 3% of those with normal baseline thyroid function developed thyroid disease
  • 3.4% of the baseline normal population developed subclinical hypothyroidism
  • 0.7% developed overt or subclinical hyperthyroidism.

There was not a statistical difference between the prevalence or incidence of thyroid disease among the various types of diabetes.

Analysis

Study author Paul Chubb MD, a senior clinical scientist in the biochemistry department at the University of Western Australia, says that the level of thyroid dysfunction he and his coauthors found with diabetes was “about what we expected.”

But what they did find surprising was that the level of thyroid disease among those with type 1 diabetes and those with type 2 diabetes was similar before adjustments were made for age and gender, he says.

“That means that for the primary care provider seeing a typical patient with type 2 diabetes, the probability of thyroid disease being present is similar to a typical patient with type 1 diabetes.” Chubb believes this is due to the fact that those with type 2 diabetes are older in the community-based cohort they studied.

That there is a significant proportion of type 2 diabetes patients who also develop thyroid conditions is not something Chubb believes should alarm patients. “But if they start showing symptoms of thyroid dysfunction, such as tiredness or unexplained weight gain, then these should be discussed with their doctor and thyroid testing considered.”

In Australia, where the study was conducted, he says that most cases of thyroid dysfunction among diabetes patients are detected by physicians. However, about 1.2% of the study cohort who had type 2 diabetes without a history of thyroid issues had signs of the disease that could be detected. “Regular thyroid testing, perhaps at 2-year intervals among this group of patients would seem advisable,” says Chubb.

Recommendations

That said, Chubb notes that there is not much good evidence about how frequently those diagnosed with diabetes should have their thyroid function tested, and the study did not examine that. Patients should not take the recommendation as a reason to insist on screening if there is no sign of thyroid disease.

In the United States, there are recommendations that those with type 1 diabetes should be screened shortly after diagnosis, he says, but that is not so for type 2 diabetes patients, despite the fact that those patients have the same likelihood of developing a thyroid disorder as the other group. “Therefore, doctors should remain vigilant for the occurrence of thyroid dysfunction among people with type 2 diabetes, as well as type 1.”

The study also found that sometimes, some abnormal thyroid hormone levels are transient, not permanent. This mimics the results other researchers have found. In this current study, Chubb and his colleagues found that more than 40% of the patients who had abnormal TSH at their baseline tests had normal TSH at the follow-up. Abnormal results should be confirmed with repeat testing, he suggests, so that there is no unnecessary treatment.

Increasing dietary iodine may help

Another recent study also found that dietary iodine intake may be responsible for some of the thyroid dysfunction among those with diabetes, and ensuring the diabetic diet includes adequate amounts may be a way to ensure this particular co-morbidity is not one that they have to endure.

Another point of interest Chubb points out is that they also looked at patients with latent autoimmune diabetes of adults. LADA is thought to account for between 2 and 10% of diabetes cases in adults. It differs from other diabetes in adults in that these patients do not need insulin treatment for at least six months after diagnosis. It is similar to type 1 diabetes, but it first occurs in adults.

The researchers found that the rate of thyroid antibody positivity among the LADA group was between the rates of those with type 1 and type 2 diabetes. However, their prevalence of thyroid disease was similar to that of the patients with type 2 diabetes. Chubb says there needs to be further study of those with LADA to confirm their observations.

Chubb says he would also like to see more research into what it means for those with diabetes to have thyroid dysfunction. “While large population studies do not show significant effects of mild thyroid dysfunction on mortality, it is possible that it may contribute to, or interact with, other co-morbidities of diabetes such as lipid metabolism and glucose handling.”

Continue Reading:
Early Detection of Diabetes Comes Through the Eyes
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