Basal Body Temperature for Thyroid Function - A Comprehensive Guide

Basal Body Temperature for Thyroid Function - A Comprehensive Guide
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It sounds like a pretty simple question, but it’s a super important answer that you need to know: what’s your temperature? Today, I want to talk to you about basal body temperature, and whether or not it has any use when it comes to predicting thyroid disease.

Basal Body Temperature and Your Thyroid

For over a century, the relationship between basal body temperature and thyroid disease has been known and well-documented. One of the earliest mentions of it was an 1888 compilation of case reports of those suffering from myxedema, which was a late consequence of severe hypothyroidism.

Many different symptoms and metrics were tracked, in hundreds of patients over many years - included in that tracking was basal body temperature. The authors discussed what was an unusually low temperature in nearly all of those with myxedema. In the years that followed, it became known that a lack of thyroid hormone was the cause of this condition and that the oral use of desiccated thyroid could cure it.

From this logic we get the work of Broda Otto Barnes. He took the idea of basal body temperature and thyroid disease one step further, and suggested that the use of basal body temperature could help with diagnosing thyroid disease - and ultimately determining the optimal dosage for those who were on replacement therapy.

What I appreciated about Dr. Barnes was his tenacity to find a solution. He saw that the tests of the day simply were not cutting it, and he ventured forth to try and figure out a new way to help people with thyroid disease. He was incredibly compassionate, and legitimately wanted to help his patients. While his methods might not have worked, as we will learn, you have to admire someone for trying to do the right thing.

Key Insight: How were tests not cutting it? Over the course of his research, Barnes saw that many blood tests were proposed to track thyroid disease, but they really were not very accurate. Keep in mind, though, that this was during a time where we did not have TSH, free T3 or free T4. Believe it or not, due to the unreliability of testing during that time, cholesterol levels were thought to be relevant for thyroid testing. It’s a good thing that we know so much about thyroid testing today (1).

In the very distant past, however, they would measure basal metabolic rate - which is what we might understand as basal body temperature. This was done by:

  • Taking your temperature in your mouth
  • Taking your temperature in your rectum
  • Taking your temperature in your armpit (axillary temperature)

Bottom Line: The truth is that, at the extremes of thyroid function, your thyroid does cause changes in body temperature. If you are very hyperthyroid, like during a hyperthyroid storm, your temperature may run higher. In the extremes on the opposite end, your temperature may run lower.

Barnes’ Research and Insight

After doing some serious thought about this, Barnes would ultimately argue that between those extreme temperatures was a strong indicator for overall thyroid status. He developed a range, between 97.8 to 98.2ºF, where a healthy person should always be. It’s pretty easy to see that this is a small range - 0.4ºF does not leave much room for error.

For Barnes, it came down to this:

  • The higher you were out of the range, the more thyrotoxic you were
  • The lower you were out of the range, the more you were hypothyroid

Bottom Line: What this essentially meant was that if your temperature was low, Barnes would encourage taking thyroid medication. Your overall temperature became the arbiter of your thyroid status - and your overall health. Basically, you would take more and more medication until you were within that optimal, and very slim, temperature range.

Is this an accurate model?

What we want to know today is how was that idea borne out, and is it accurate to tie body temperature and thyroid status together? These are the questions that we need answers to, and that can help give us a better read on our health.

Where’s your temperature supposed to be? You might have heard of the 98.6ºF. While this might seem like a legend to some, it actually came from a large number of data points in the 1900’s. The initial argument was that, for a big population, this would simply be the average temperature - not the optimal temperature, by any means.

Bottom Line: A recent study showed that the average temperature has gone down from the initial findings way back when, but they also found that healthy people can have varying temperatures of all kinds. People can be just about anywhere, and have no problems at all.

What does this mean for Barnes’ work?

Well, it means that the range he was trying to rely on (97.8 to 98.2ºF) is not indicative of good or bad health, necessarily. It means that the range is way broader for healthy people, and that a slim range like this just does not work. It would mean that around 98% of the population would need to be put on thyroid medication of some kind.

Does your thyroid regulate basal body temperature?

The short answer is no. The long answer is that although your thyroid is a key player in regulating metabolism and temperature, there are a cascade of other hormones and messenger molecules that are at work. Like we discovered before, even healthy and fit people do not fall within the optimal range of basal body temperature - does this mean that they should go on thyroid medication? Not at all.

The internal factors at work influencing your temperature include:

  • Leptin
  • Epinephrine
  • Norepinephrine
  • Cytokines

Basal body temperature is governed by so many internal and external factors, and not just the thyroid gland itself - in this way, we cannot tie any recommendations to how you should treat your thyroid to your temperature alone. When it comes to external factors, we can also understand that:

  • The season
  • The time of day
  • Your diet
  • Other menstrual factors
  • Circadian variations

Bottom Line: All of these factors play an important role in your basal body temperature, so why would we ever just attribute it to the function of your thyroid? While testing might not have been as nuanced in the past, where an answer was needed and people needed to be helped, today we can have a much more nuanced understanding of these factors and how your thyroid works alongside them.

The next question we might be wondering is, “does your thyroid have a role to play in the linear status of that range?” In a group of trauma patients, one study recorded their axillary temperatures with thyroid scores from current accurate tests. What they found was that almost everyone was outside of Barnes’ “optimal” range for thyroid patients. Those that had thyroid abnormalities, there was also no relationship between that and their blood pressure.

Are you only thyrotoxic when your temperature goes up?

In other words, is it safe to take more thyroid medication until your temperature goes up to 98.2ºF? The simple answer is no, that it is unfortunately not true. With hyperthyroidism, there is one version that we know as thyrotoxic storm. This is so bad for you, and is an emergency room situation that is not good for you in the slightest.

What we know about it, though, is that in some cases a fever will show up during a hyperthyroid storm. But, it is not that when your thyroid dose gets higher that you make a steady track up to hyperthyroid storm.

Bottom Line: If your temperature is going up, up, up, it is most likely not due to you being thyrotoxic - except in some incredibly serious situations where you might need to go to the hospital.

Big Picture: Basal Body Temperature

What we need to know is that basal body temperature was a useful thing in history, and that it is a helpful thing to track fertility and your menstrual cycle. You can see shifts in that, but we know that it is not a good tool to track changes in your thyroid. Please know that your temperature is important, but that not everyone has a high one. If you are not in Barnes’ optimal range, I would not worry about your long-term health - this is just the way you are. You cannot rely on it alone to see if your thyroid dose is safe enough.

What we know, with our present knowledge, is that basal body temperature cannot be safely relied upon to prevent hyperthyroid effects of thyroid therapy. The problem is that hypothyroidism is a highly prevalent condition, and that many who would benefit from treatment remain undiagnosed - can you just imagine how many people back in the day went undiagnosed?

The best way to find out if someone has a thyroid condition is to test, don’t guess, and by considering these key variables:

Differential Diagnosis

Understanding the root cause of your illness, this is the stage where you might be able to rule out other symptoms so that you can gain a clear understanding of how your health is changing and what other factors might be at play.


Symptoms are always important, and being able to recognize them is just as important. While testing can give you a clear picture of your health, acknowledging and understanding your symptoms can help you understand how these things make you feel.

Thorough Blood Tests

There are plenty of tests that you can consider, such as:

  • TSH
  • Free T3
  • Free T4
  • Thyroglobulin
  • Thyroid Antibodies

Structural Findings

This is all about figuring out the structural health of your thyroid. For your health, you need to understand the physical mass, size, and health of your thyroid by feeling it. This can be done by:

  • Getting an ultrasound
  • Self-exams
  • Yearly doctor’s exams

What we know today is that we do not have to rely on our basal body temperature to give us a good idea of our thyroid’s health, and we also do not have to rely on a range of temperature that can be virtually impossible for even perfectly healthy people to fall within. What we have now are reliable blood tests, examinations, and other methods that can really give us a fuller picture of our health.

Bottom Line: In my opinion, one of the greatest gifts that Barnes has left us is a healthy skepticism toward medical progress and a respect for the insights of those who have gone before us. If he did not question testing of the thyroid, we might not be at the point we are at today, and for that we can thank him.

Learning About Your Thyroid Today

Want to learn about a test that can give you a clearer picture about the performance of your thyroid? We talked today about how you can avoid your basal body temperature as a significant indicator of your thyroid health, instead you should turn your attention to learning more about your thyroid with the Thyroid Quiz right now (2). This quiz will give you a great starting point, and can help guarantee your health in the future. Learn more about your thyroid today, and get on the path to feeling better - without having to worry about your temperature.

Dr. Alan Glen Christianson (Dr. C) is a Naturopathic Endocrinologist and the author of The NY Times bestselling Adrenal Reset Diet.

Dr. C’s gift for figuring out what really works has helped hundreds of thousands of people reverse thyroid disease, lose weight, cure diabetes, and regain energy. Learn more about the surprising story that started his quest.

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