This article is part of a special report on Thyroid Disorders. To see the other articles in this series, click here.
According to the American Association of Clinical Endocrinologists, 27 million Americans suffer from thyroid dysfunction – half of whom go undiagnosed. Subclinical hypothyroidism, a condition in which TSH is elevated but free T4 is normal, may affect an additional 24 million Americans. Taken together, more than 50 million Americans are affected by some form of thyroid disorder.
Metabolic syndrome (MetS), also affects 50 million Americans, and insulin resistance, one of the components of metabolic syndrome, affects up to 105 million Americans. That’s 35% of the population. Metabolic syndrome has become so common that it’s predicted to eventually bankrupt our healthcare system. Both metabolic syndrome and insulin resistance are risk factors for heart disease and diabetes, two of the leading causes of death in the developed world.
With such a high prevalence of both thyroid dysfunction and metabolic syndrome, you might suspect there’s a connection between the two. And you’d be right.
That’s because healthy thyroid function depends on keeping your blood sugar in a normal range, and keeping your blood sugar in a normal range depends on healthy thyroid function.
How high blood sugar affects the thyroid
Metabolic syndrome is defined as a group of metabolic risk factors appearing together, including:
- abdominal obesity;
- high cholesterol and triglycerides;
- high blood pressure;
- insulin resistance;
- tendency to form blood clots; and,
Metabolic syndrome is caused by chronic hyperglycemia (high blood sugar). Chronic hyperglycemia is caused by eating too many carbohydrates. Therefore, metabolic syndrome could more simply be called “excess carbohydrate disease”. In fact, some researchers have gone as far as defining metabolic syndrome as “those physiologic markers that respond to reduction in dietary carbohydrate.”
When you eat too many carbs, the pancreas secretes insulin to move excess glucose from the blood into the cells where glucose is used to produce energy. But over time, the cells lose the ability to respond to insulin. It’s as if insulin is knocking on the door, but the cells can’t hear it. The pancreas responds by pumping out even more insulin (knocking louder) in an effort to get glucose into the cells, and this eventually causes insulin resistance.
Studies have shown that the repeated insulin surges common in insulin resistance increase the destruction of the thyroid gland in people with autoimmune thyroid disease. As the thyroid gland is destroyed, thyroid hormone production falls.
How low blood sugar affects the thyroid
But just as high blood sugar can weaken thyroid function, chronically low blood sugar can also cause problems.
Your body is genetically programmed to recognize low blood sugar as a threat to survival. Severe or prolonged hypoglycemia can cause seizures, coma, and death. When your blood sugar levels drop below normal, your adrenal glands respond by secreting a hormone called cortisol. Cortisol then tells the liver to produce more glucose, bringing blood sugar levels back to normal.
The problem is that cortisol (along with epinephrine) is also a sympathetic nervous system hormone involved in the “flight or fight” response. This response includes an increase in heart rate and lung action and an increase in blood flow to skeletal muscles to help us defend against or flee from danger. Cortisol’s role is to increase the amount of glucose available to the brain, enhance tissue repair, and curb functions – like digestion, growth and reproduction – that are nonessential or even detrimental in a fight or flight situation.
Unfortunately for hypoglycemics, repeated cortisol release caused by episodes of low blood sugar suppresses pituitary function. And as I showed in a previous article, without proper pituitary function, your thyroid can’t function properly.
Together, hyperglycemia and hypoglycemia are referred to as dysglycemia. Dysglycemia weakens and inflames the gut, lungs and brain, imbalances hormone levels, exhausts the adrenal glands, disrupts detoxification pathways, and impairs overall metabolism. Each of these effects significantly weakens thyroid function. As long as you have dysglycemia, whatever you do to fix your thyroid isn’t going to work.
How low thyroid function affects blood sugar
We’ve seen now how both high and low blood sugar cause thyroid dysfunction. On the other hand, low thyroid function can cause dysglycemia and metabolic syndrome through a variety of mechanisms:
- it slows the rate of glucose uptake by cells;
- it decreases rate of glucose absorption in the gut;
- it slows response of insulin to elevated blood sugar; and,
- it slows the clearance of insulin from the blood.
These mechanisms present clinically as hypoglycemia. When you’re hypothyroid, your cells aren’t very sensitive to glucose. So although you may have normal levels of glucose in your blood, you’ll have the symptoms of hypoglycemia (fatigue, headache, hunger, irritability, etc.). And since your cells aren’t getting the glucose they need, your adrenals will release cortisol to increase the amount of glucose available to them. This causes a chronic stress response, as I described above, that suppresses thyroid function.
How to keep your blood sugar in a healthy range
It’s important to understand that whether you have high or low blood sugar, you probably have some degree of insulin resistance. I described how high blood sugar causes insulin resistance above. But insulin resistance can also cause low blood sugar. This condition, called reactive hypoglycemia, occurs when the body secretes excess insulin in response to a high carbohydrate meal – causing blood sugar levels to drop below normal.
In either case, the solution is to make sure your blood sugar stays within a healthy range. There are two targets to consider. The first is fasting blood glucose, which is a measure of your blood sugar first thing in the morning before eating or drinking anything. I define the normal range for fasting blood glucose as 75 – 95 mg/dL. Although 100 is often considered the cutoff for normal, studies have shown that fasting blood sugar levels in the mid-90s were predictive of future diabetes a decade later. And although 80 mg/dL is often defined as the cutoff on the low end, plenty of healthy people have fasting blood sugar in the mid-to-high 70s (especially if they follow a low-carb diet).
The second, and much more important, target is post-prandial blood glucose. This is a measure of your blood sugar 1-2 hours after a meal. Several studies have shown that post-prandial blood glucose is the most accurate predictor of future diabetic complications and is the first marker (before fasting blood glucose and Hb1Ac) to indicate dysglycemia.
Normal post-prandial blood sugar one to two hours after a meal is 120 mg/dL. Most normal people are under 100 mg/dL two hours after a meal.
Now that we know the targets, let’s look at how to meet them. If you’re hypoglycemic, your challenge is to keep your blood sugar above 75 throughout the day. The best way to do this is to eat a low-to-moderate carbohydrate diet (to prevent the blood sugar fluctuations I described above), and to eat frequent, small meals every 2-3 hours (to ensure a continuous supply of energy to the body.
If you’re hyperglycemic, your challenge is to keep your blood sugar below 120 two hours after a meal. The only way you’re going to be able to do this is to restrict carbohydrates. But how low-carb do you need to go? The answer is different for everyone. You figure your own carbohydrate tolerance by buying a blood glucose meter and testing your blood sugar after various meals. If you’ve eaten too many carbs, your blood sugar will remain above 120 mg/dL two hours after your meal.
I highly recommend you pick up a blood glucose meter if you have a thyroid and/or blood sugar problem. It’s the simplest and most cost-effective way to figure out how much carbohydrate is safe for you to eat. There are tons of meters out there, but one that gets a lot of good recommendations is the ReliOn Ultima. It’s pretty cheap, and the test strips are also cheap, which is where the major expense lies.
Finally, if you have poor thyroid function it’s important that you take steps to normalize it. As I’ve described in this article, the cycle works in both direction. Dysglycemia can depress thyroid function, but thyroid disorders can cause dysglycemia and predispose you to insulin resistance and metabolic syndrome.