High Blood Sugar Impacts Thyroid Function
Most people understand that sugary foods are not the healthiest for their body and over consumption of refined carbohydrates are tied to unwanted weight gain.
However, few people realize that the fluctuations in blood sugar related to excess carbohydrates can wreak havoc on the thyroid gland.
Not only do blood sugar spikes impact the thyroid, but we also know that foods like bread, pasta, sugar and various desserts can cause or exacerbate autoimmune thyroid conditions like Hashimoto’s Disease. 
Making matters worse, thyroid dysfunction, in turn, causes more glucose regulation issues.
The Blood Sugar-Thyroid Cycle
- A high carb diet causes glucose levels to fluctuate 
- Glucose fluctuations increase cortisol (stress hormone) 
- Too much cortisol causes hypothyroidism 
- Hypothyroidism causes insulin resistance 
- Insulin resistance causes high blood glucose 
- High blood glucose causes more insulin release
- More insulin causes glucose levels to crash (initiating cravings)
- The cycle continues
These hormone patterns become a vicious circle that is self-reinforcing, creating what is called a positive feedback loop.
As medical research clearly shows, hypothyroidism and diabetes are closely linked together.
Knowing that hypothyroidism and diabetes are connected, addressing either of these conditions should be done in a holistic fashion that balances both systems – glucose and thyroid regulation at the same time.
This is another reason why a Functional Medicine approach is far superior to conventional medical treatments of glucose and thyroid conditions.
Low Blood Sugar Impacts Thyroid Function
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.
When your blood sugar levels drop below normal, your adrenal glands respond by secreting cortisol (a primary stress hormone).
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.
Unfortunately for hypoglycemics, repeated cortisol release caused by episodes of low blood sugar suppresses pituitary function.
Without proper pituitary function, your thyroid can’t function properly.
So high blood glucose and low blood glucose can both impact thyroid function.
Together, hyperglycemia (high glucose) and hypoglycemia (low glucose) 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 and as long as you have dysglycemia (imbalances in glucose), whatever you do to fix your thyroid isn’t going to work.
Thyroid Disorders Impact Blood Sugar
We’ve already discussed how high and low blood sugar can cause thyroid dysfunction.
It's equally important know that poor thyroid dysfunction can cause dysglycemia and metabolic syndrome through a variety of mechanisms: 
- slows the rate of glucose uptake by cells;
- decreases rate of glucose absorption in the gut;
- slows response of insulin to elevated blood sugar; and
- slows the clearance of insulin from the blood.
These mechanisms present clinically as hypoglycemia.
When someone has hypothyroid, their cells aren’t very sensitive to glucose.
So although they may have normal levels of glucose in their blood, they’ll have the symptoms of hypoglycemia (fatigue, headache, hunger, irritability, etc.).
And since the cells aren’t getting the glucose they need, the adrenals will release cortisol to increase the amount of glucose available to them.
This causes a chronic stress response that further suppresses thyroid function.
How to Balance Your Blood Sugar
When it comes to balancing blood sugar, the first step is to get a running average of what your blood sugar is doing.
To do this, there are two targets that you want to start tracking:
- Fasting Blood Glucose
- Post-Prandial Blood Glucose
Fasting blood glucose is a measure of your blood sugar first thing in the morning before eating or drinking anything.
I would consider a normal range for fasting blood glucose to be anywhere from 75-105 mg/dL and optimal ranges to be between 75-85 mg/dl.
Generally speaking, 100 mg/dl is the cutoff for normal and studies have shown that fasting blood sugar levels above 95 had more than 3X the risk of developing diabets compared to people below 95 mg/dl. 
Another study showed progressively increasing risk of heart disease in men with fasting blood glucose levels above 85 mg/dL, as compared to those withlevels of 81 mg/dL or lower. 
Post-prandial blood glucose 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.
A continuous glucose monitoring study showed that sensor glucose concentrations were between 71 – 120 mg/dL for 91% of the day, whereas values were less than or equal to 60 or 140 mg/dL for only 0.2% and 0.4% of the day, respectively. 
This suggests that if post-meal blood sugar rises above 140 mg/dl and stay there for a significant part of the day, health consequences are severe.
Now that we understand what is normal and expected, I'd suggest anyone with thyroid problems to start tracking their fasting blood glucose and post-prandial blood glucose to get an idea of where they are.
If you’re hypoglycemic (low blood glucose), 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 (high blood glucose), 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.
I would start by figuring out how my carbohydrate tolerance by buying a blood glucose meter and testing my blood sugar after various meals.
If you eat too many carbs, your blood sugar will remain above 120 mg/dL two hours after your meal.