Thyroid, Blood Sugar, and Metabolic Syndrome | Chris Kresser

Thyroid, Blood Sugar, and Metabolic Syndrome

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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. It’s also closely related with diabesity.

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.

Studies show an increased frequency of thyroid disorders in diabetics, and a higher prevalence of obesity and metabolic syndrome in people with thyroid disorders.

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.

Thyroid, Blood Sugar, and Metabolic Syndrome

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,
  • inflammation.

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.

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  1. About a year ago I have been diagnosed with bad thyroid and was on meds and stoped them about 6 months ago and suger was fine and now a year later I was retested and NOW my thyroid is FINE but my blood suger level 130. I have been eating completely bad food for the past six months and even day before the test I ate bunch if Arby’s and nutty bars and whatever. But I didnfast for the 12 hours over night during sleep. So what is going on is it possible thyroid healed and my suger is high because if all the crap foods I have been eating or is it possible I’m a diabetic? Or since I have been eating so bad and my metabolism is really slow that 12 hours wasn’t enough to drop my suger back down?

  2. I have reactive hypoglycemia after a meal sometimes 30 mins later it drops to 80s. Sometimes I don’t know if a meal will drop it instantly or bring it up like it should. I have cut out all the sweets and white bread. I eat wheat rarely. I do drink sweet tea bc if not it drops to 70s. Never seen it below 66. I also am on thyroid medicine 50mg because they said it was too high. I have also gained 100 pounds in a year. I need advice on getting my life back and what could be going on. Someone had said my thyroid medicine wasn’t high enough. Also I know I had a candida infection that said it is linked to reactive hypoglycemia. In am currently waiting on results for that. I think something has caused this. I do not have anyone in my family with hypoglycemia.

  3. Thank you very much for your help in clarifying the relationship between Iodine and blood sugar level. This is the best article on the subject so far.

  4. An amazing factual right to the point article about Iodine and relationship to blood sugar.
    Thank you so very much for your help in clarifying the subject.

  5. I am fascinated that the Thyroid and Blood Sugar are connected. I was diagnosed with pre-diabetes about 5 years ago and put on Metformin. My fbs has never been great, but usually right around 100. My post meal bs has been usually around 115-120. About 3 months ago, I was also diagnosed as hypothyroid and put on 25 mg Synthroid, then moved to 50 mg Synthroid after 6 weeks. Now, my fbs is 143. Help! Now what do I do? I am slightly overweight at 137lbs (5’4″). Will loosing weight make a difference? Are there supplements that can help?

    • I have found plant supplements that are very clean with no artificial dyes or ingredients that relate blood sugar. It has helped both stabilize my blod sugar and thyroid function.

    • This has happened to me too! Why is the thyroid med affecting my blood sugar? My diet is ketogenic and super clean.

      • Because levothyroxine suppresses hypothalamic function, which also governs blood sugars. Switch to ARmour thyroid.

  6. I do have thyroid issues which they say now is back in line. I think I have reactive hypoglycemia. About a hour after a meal my sugar is in the 80s. Does anyone know if you have a high fasting insulin if it can cause the reactive hypoglycemia?

    • I am also having thyroid and reactive hypoglycemia issues and now I’m over weight. I want to follow your feed. Dealing with it for several months now. 🙁

  7. I am hypoglycemic and have been on a metabolic diet for a year now to help balance it (worked flawlessly). I also have hypothyroid that I take armour thyroid for it to keep levels normal. In the past few months, I have started to gain weight fast, I feel nauseated, everything I eat (healthy) my body responds like I am feeding it sugar, and my face oddly feels numb all day. I have been going to the doctor to find the problem. My progesterone levels are normal, my thyroid levels are normal, blood pressure is normal, and I have been on gut medication for 3 weeks with no results. I am wondering if, despite being on a diet, I could be pre diabetic? My insulin was 2 points lower than normal on an all-around blood test, but I am wondering if I should take an insulin resistance test to get a more clear reading?

    • Sounds like Adrenal Fatigue. Both Thyroid and Adrenal Glands are intimately linked together… Take 3000mg Vitamin C and 500mg Magnesium… Avoid yeast (this includes msg, vinegar, citric acid – its made from mold not citrus btw look it up), carbohydrates, and sugar at all costs, this includes starches (breads, pastas, etc…)… Basically, you need to change to a Meats Fruits and Vegetables ONLY Diet…Anyway, look it up. I’m going through the same basically. Good Luck.

    • Check your thyroid T3 and T 4 levels. Finally after years of doc telling my thyroid was normal, it wasn’t .
      Also there are additives in food today that are not labeled MSG, but for me I get an attack and black out. If a product says “yeast” it is a flavor enhancer and in just about everything

    • Diet is 80% of it, but the other 20% key to restoring your health is physical activity. Walking is an easy way to start, but even easier is to simply start by doing stretches that feel good! You can just sit on the floor or even on your couch and stretch your legs and arms in ways that feel satisfying, not overdoing it. Slowly increase your stretch and after a few weeks when you are then sleeping better and your joints and muscles are all feeling better too, bring in another activity. I really like jumping rope, because it only takes a few minutes to get your blood pumping, and it’s fun! When I started I was absolutely exhausted before 70 jumps (that is maybe a minute of exercise) so that is where I’d stop (stop when you’re exhausted) I have not been doing it long but I am now nearing 150 jumps. It’s fun to see progress.

      I highly suggest adding a physical activity regime alongside your healthy eating, something simple like this. It can really do wonders if you stick to it. Write what you did (or if you skipped workout that day) every day in a journal, and write out the next day’s date on the next page after you are finished as motivation to then actually fill it out the next day.

      (PS I suggest doing the jump rope in runners, it feels better than barefoot.)

  8. Hi, Chris. I love your information and am grateful. I also downloaded the free Thyroid Disorders ebook (thank you!), which had some good stuff; however, there wasn’t much in the ebook in the way of hyperthyroidism (specifically Grave’s Disease) and the roll of insulin resistance; the focus seemed to be mostly on hypothyroid/Hashimoto’s or autoimmune in general. My interest is because about a year ago I was diagnosed with GD. For the record the past couple of weeks I have been eating very low carb and also going through a basic elimination diet (including gluten and dairy) in an attempt to see what works, and I do feel better (though I don’t know if this is due more to the low-carb or the cutting out of dairy and gluten, etc, or both). I’ve read a paper by Drs. Tsai, Winer, et al about Diabetes Type 2 (http://diabetes.diabetesjournals.org/content/64/6/1886.long) and would love to hear your thoughts. Thanks!

  9. I have hypothyroidism. My TSH levels sometimes fluctuate so that I have to alter my synthroid dosage. I am very symptomatic of hypoglycemia yet my blood level tests show me as normal. I’ve done the six hour glucose test and have checked my blood at home, all normal. My doctor sent me to an endocrinologist and she said there is no connection of my symptoms to my thyroid. I usually have to eat 2 hours after breakfast and lunch yet I can go all evening after dinner until the next day, so my symptoms are worse during the day – weird right. Do you know what condition I have if it’s not hypoglycemia? Thanks.

    • You are just like me! I have just been diagnosed with Hirata’s Syndrome. I don’t know a whole lot about this syndrome as of yet, except it is an autoimmune situation. You might want to check into it though.

      • Dana, thank you for your response. I find it so disheartening that my doctor and the specialists don’t know what condition I have. A dietician said she feels it’s reactive hypoglycemia. I’d be interested to know how you came to get your diagnosis? Thanks.

          • Thank you for commenting on my post. I don’t take any medications at all. However, I do have Grave’s Disease and several other autoimmune disorders. My doctor prescribed Metformin to help with the insulin use. I am hoping it will help.

        • Hey, Nina! My endocrinologist has spent many moons testing me for different things. I do have several autoimmune disorders–one of which is Grave’s Disease. Many times, folks develop Hirata’s after Grave’s Disease. I am not on any medications for that right now because my Grave’s Disease is intermittent. I am not sure if you have been tested for any type of thyroid problems, but that is always a first stop for many things. I am hoping you do find something to help you—and quickly. It is very discouraging to not know what’s going on inside of you! My master’s is in public health and my doctorate is in naturopathy for that very reason!

          • Hi Dana and April, thanks so much for your comments. I’m going to mention Hirata’s Syndrome to my doctor.
            You mentioned sulfhydryl compounds but I’m not taking any meds except for Synthroid for my hypothyroid. However, something occurred to me which maybe completely unrelated…I am addicted to using Blistex. I decided to read the ingredients which includes Padimate and Oxybenzone. When reading about this ingredient it made reference to sulfa drugs. I know this may be a bit of a stretch. Anyway, it might be worth a try getting off the lip balm.

            The other thing worth mentioning is that my hypoglycemic episodes came about at the same time my thyroid went out. This can’t be a coincidence.

  10. Read a study the other day that tested a variety of foods for their insulinogenic effect… Beef came out top – what do you make of this?

    The theory is that fat in the blood stops insulin from being used effectively by the cells to uptake glucose – and proponents of this say excess fat is the real cause of diabetes.

    I’m not sure yet either way, but surely excess fat in the blood would either be caused by a slow liver or by excess weight. And surely the problem would be compounded by refined carb intake. So perhaps it is the combination of the 2 which causes the damage?

  11. I have hypothyrioid and nodules on my thyroid. The doctor tried medicine to see if it helped and it did not work so he took me off it. I had gastric bypass in 2010 because health issues. Now I started to have seizures and black out because my blood sugar bottoms out & I feel it happens when my thyroid decides to work and wipes out what sugar I do have in my system. Can anyone give any advice what my next step should be or what to do so I quit having the seizures ?

    • Disclaimer: Not a doc, take advice with a grain of salt.

      First thing, get your diet right. Take out ALL restaurant food. No more eating out EVER. Eat foods as close to what you would find in nature as possible (think Paleo with wild caught fish for your protein, iodine, and DHA source).

      Especially eliminate high-fructose corn syrup and other added sugars from your diet (these could be the cause of those hypoglycemic episodes you said you are having). If it’s high in carbs, low in natural fiber and it didn’t grow on a tree, picked from a bush or vine, or get pulled from the ground, probably don’t eat it.

      Do research on hypothyroidism. Read research papers online. Stick with the science. Doctors are dangerous (they almost always want to give drugs, not assay and fix the actual problem), but research papers can be very illuminating.

      Almost all issues can be cleared up with good food and good exercise or the elimination of bad food, but it takes time. Sometimes years.

      The important thing is sticking with the most healthy diet you can eat and getting regular weight-bearing exercise in your life.

      If you are having hypoglycemic episodes either due to the bariatric surgery (because now your stomach is compromised) or your thyroid, I advise you to get some glucose tablets to have on you at all times.

      Since you are limited to the amount of food you can put in your stomach, you must eat the most nutritionally dense foods on the planet.

      I hope these simple things will at least put you on the right track.

    • I jave successfully stopped hypoglycemia AND seozures by using Progesterone. I was estrogen dominant at Peri menopause and it was hell. Now 5 years later and now i am fine still. I was started st first on Prometrium then i switched to cream. I also use Estrosmart to keep estrogen at bay. For some reason i have trouble clearing it out of my system. I also have been prescribed Erfa thyroid 2 grains. Much improved overall.

      • That would make sense as progesterone is one of the hormones needed to make cortisol and cortisol is required to increase blood sugar levels ? if you are having trouble clearing out excess oestrogen I would suggest you get some liver herbs and dim which will help clear out excess hormones by enhancing liver detoxification pathways (student nat)

  12. I have Hashimoto and eat a relatively low carb diet, carbs are mainly from green vegetables and berries/apples. For past four months my fast glucose is 122, and then 112 after eating. I am stumped my fasting blood is consistantly too high even though I am eating limited to no sugar or carbs. How is it showing this elevated readings, the day before my last fasting blood test, I ate 88 g carbs- fruit and veggies and the results were 122. Dr said limited carbs and sugar, but offers no advice when I tell her I am not eating sweets, processed foods, etc. Any insight because, can I be getting a false reading somehow?

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