There are a lot of connections between thyroid and blood sugar control, such as metabolic rate and mitochondrial function.

There is also a strong indication – according to a study published earlier this month by The Endocrine Society – that the thyroid hormone T3 controls and regulates the release of insulin, suggesting that low thyroid function could raise the risk of developing type 2 diabetes, especially in people with prediabetes.

The study, involving nearly 8.500 people, has found that among participants presenting a mild elevation in blood glucose, those with hypothyroidism or even low-normal thyroid function had a 13 per cent higher chance of developing type 2 diabetes and that risk rose up to 40 per cent for people with prediabetes.

A 2003 study also found thyroid disorder to be more common in diabetic females than males.

In this new study, 1,100 participants ended up developing prediabetes while 798 developed type 2 diabetes over the course of an average follow-up lasting nearly eight years.

We have known for years that undiagnosed thyroid disease leads to type 2 diabetes. Yet so few physicians ever test patients with prediabetes or slightly high blood sugars for thyroid disease.

For the lead investigator of the study and MD of the Erasmus Medical Center in Rotterdam, Layal Chaker, these findings indicate that screening people with prediabetes for low thyroid function should be systematic.

Most experts currently recommend thyroid screening only for people with type 1 diabetes, as they have a greatly increased risk of thyroid disease.

Yet balanced thyroid hormones are essential to metabolic health. When out of whack they have the power to deregulate fat storage and insulin release, two risk factors for type 2 diabetes.

Low thyroid function could raise the risk of developing type 2 diabetes, especially in people with prediabetes.

It is thought that the thyroid hormone T3, especially, directly controls insulin secretion whereby the insulin goes down in response to low thyroid.

Getting the T3 hormone into the cells, which helps preserve beta cell function – and is essential for blood sugar control – requires healthy cortisol levels. High cortisol levels prevents the conversion of the inactive form of the thyroid hormone T4 into the active form T3 in the peripheral tissues.

When insulin is reduced due to low thyroid hormone, excess sugar can’t be shuttled out of the bloodstream into the cells to be utilised.

Researchers were surprised to find that even people whose thyroid function was in the low-normal range had an increased risk of diabetes, which suggests two things: either the association of thyroid function with type 2 diabetes remains unclear – and we know that it’s now well-documented – or people get tested improperly for low thyroid.

A routine preliminary test usually includes the Thyroid-Stimulating Hormone (TSH), which is regularly reported as being an often misleading and unreliable marker of the body’s overall thyroid status.

It is inversely correlated with pituitary T3 levels that are physiologically influenced by things like stress, depression, inflammation or chronic fatigue, that stimulate local mechanisms to increase them accordingly. Often tests will thus come back borderline, normal or at the high end of the normal range.

Instead, recommends Rph Suzy Cohen at the on-going Diabetes Summit 2016, the right tests to ask for include reverse T3, which numbers should be less than 15 or 150, Ferritin 9 (a form of iron) of 70 to 90, Thyroid Peroxidase Antibody (TPO) antibodies (which, if high can indicate that the cause of thyroid disease is an autoimmune disorder such as Hashimoto’s) and basal body temperature, which should be greater than 97.8 upon waking up.

Warning signs to look out for when suspecting a low thyroid function include: being overweight, insulin resistant, changes in mood and apathy, lower sex drive, anxiety, panic attacks, arthritis, joint pain, slow digestion and depression. Unsurprisingly, these symptoms are also very similar to those of high blood sugar or type 2 diabetes.

Screening people with prediabetes for low thyroid function should be systematic – Layal Chaker, MD at the Erasmus Medical Center in Rotterdam.

People with diabetes or with elevated blood sugar are going to have higher levels of oxidative stress, the body’s natural response to inflammation, and it plays a big part in adrenal regulation too.

When the body is in a high inflammatory state, it makes more cortisol. Cortisol is the hormone we make to fight inflammation. Add to that a poor diet with highly inflammatory food to create the perfect storm for adrenal burnout.

Blood sugar and adrenal problems go hand in hand. Adrenal failure leads to an inability to adapt or cope with the inflammation.

When the adrenal glands get worn out, the body’s natural inflammatory control mechanism is gone and this negatively impacts the liver. One of the things that then happens as a side effect to that is excessive insulin production, which encourages fat storage.

A 2011 mice study looking at the role of thyroid hormone on insulin signalling and insulin resistance has found that treatment with exogenous T3 can slow down this inflammatory cascade by decreasing blood glucose and reversing insulin resistance.

Apart from HbA1c, which measures the amount of glycation (brought about by oxidative stress) to red blood cells all over the body, elevated C-Reactive Protein (CRP) in the blood also signals high levels of inflammation and has been described in number of studies as a risk factor with type 2 diabetes, gestational diabetes and metabolic syndrome.

It was also the object of a 2004 study into the development of type 1 diabetes in children.

Apart from diligent testing, ensuring good thyroid function alongside diabetes medication relies on watching out for deficiencies and restoring nutrients that the body has been depleted of as a result of adrenal burnout.

Although they can’t replace drugs prescribed for neither the treatment of diabetes or thyroid dysfunction, dietary supplements can be used to good effect under medical supervision to stay metabolically fit.

Preliminary studies in human models have for example described how antioxidants like resveratrol can curb the detrimental effect of oxidative stress on the body and how using adaptogens like ashwagandha or, even better, holy basil (that also help with glucose metabolism) would help regulate cortisol secretion.

Get our free newsletters

Stay up to date with the latest news, research and breakthroughs.