Why measure your basal body temperature?
For starters, it’s a cheap way to assess your thyroid status (helpful for weight loss and fertility), your adrenal status (helpful to understand your energy levels) and for assessing if you are ovulating (again helpful for fertility).
You can potentially get all of this valuable information by simply checking your basal body temperature each and every morning with a basal thermometer.
It’s not 100% accurate but it’s a cheap and effective way to gather valuable insight about your body.
If you want to understand more about how and why you should be checking your basal body temperature keep reading:
Basal Thermometers Give you Insight into 3 Hormone Systems in the Body
In the most basic sense, your body temperature provides insight into how much energy your body is producing at rest.
The higher amount of energy you burn at rest the more heat your body produces which is reflected in your basal body temperature.
What is more interesting is that several hormones influence your basal body temperature and therefore reflect how much energy your body is burning.
This is incredibly important when we talk about weight loss.
Because over 90% of the calories you burn are burned away by simply maintaining bodily functions (breathing, sleeping, eating, thinking, etc.).
Most people (probably you at some point) focus on the number of calories you burn that are within your control – meaning the excess calories you burn with exercise.
But think about it this way:
Even if you triple the number of calories you burn with exercise you are only influencing less than 10% of the total amount of calories your body burns each day.
It’s far better to focus on your basal body temperature and increase that number because it represents a much larger fraction of your total calories burned.
But before we get too much into weight loss, let’s talk about these hormone systems and how they each alter your body temperature:
Thyroid Hormone and Your Basal Body Temperature
Everyone knows that one of the most common side effects of hypothyroidism is weight gain (1), but did you ever stop to think about why? (for a full list of hypothyroid symptoms check out this post)
Thyroid hormones directly influence energy production at the cellular level.
So as we discussed above:
Low cellular energy production = decreased heat production = decreased body temperature = slower metabolism = weight gain.
This is obviously a very simplified version of what is happening, but it helps illustrate the point.
So if we know that body temperature is related (at least somewhat) to thyroid hormone status in your body, it follows that we should be able to track thyroid function by checking basal body temperature.
At that certainly seems to hold true in many instances like this study (2).
Patients undergoing T3 therapy for hypothyroidism do in fact show an increase in their basal body temperature which can be useful to monitor their thyroid status and overall symptoms.
In fact, you can even see an example from one of my patients below:
This example clearly shows what happens to body temperature as thyroid hormone is given to a hypothyroid patient.
The beginning shows a very chaotic and low body temperature that quickly becomes regulated both during and after ovulation after starting on Armour thyroid.
Pretty interesting, right?
So I’m saying that if you have hypothyroidism and you are currently being treated with some sort of thyroid hormone (levothyroxine, Armour thyroid, WP Thyroid, or T3) you should be able to track your basal body temperature to see if that medication is working for YOU.
Testing your basal body temperature can be particularly helpful if you are being treated but still remain symptomatic despite having “normal” labs.
If this is the case then you might either be under-treated or have other hormone imbalances contributing to your body temperature.
Adrenal Function and Basal Body Temperature
No doubt you’ve heard of the idea of adrenal fatigue.
The concept is that your adrenal (stress response system) system in your body can become overloaded and therefore “poops” out over time causing a reduction in adrenal hormones.
This concept originated from the general adaptation syndrome (3) proposed decades ago but has never been proven to be true.
Does that mean the concept of adrenal fatigue doesn’t exist?
Hardly, it just means that we probably don’t understand this condition very well.
Adrenal fatigue probably refers to a combination of hypercortisolism, hypocortisolism, and cortisol receptor resistance which manifest as the symptoms of “adrenal fatigue”.
You know, the symptoms like:
- Feeling wired but tired
- Having a boost of energy at night
- Salt and sugar cravings
- Debilitating and crushing fatigue
- Getting a “second wind” of energy late in the night
- Crashing around 2-3 pm and feeling like you need a nap
I know these symptoms well because I went through them during/after residency and was able to treat myself.
In fact, you can see my cortisol test below:
What is interesting about the adrenals is that they produce a combination of hormones ranging from sex hormones to adrenaline.
It’s the adrenaline I want to talk about for a minute:
The autonomic nervous system likely plays an important role in many of the symptoms of adrenal fatigue (wired but tired, etc.) but it also plays a role in regulating your body temperature as well (4).
That means your basal body temperature can be used as another measure of “adrenal status” in your body.
Of course, it’s not the most accurate way to measure cortisol, and adrenal function – but it can help provide insight into your body.
Generally, those with autonomic issues and cortisol dysregulation show a chaotic basal body temperature that bounces up and down day to day.
Some changes would be considered normal, but large swings of 1-2 degrees of body temperature may be indicative of adrenal dysregulation (5).
Ovulation and Sex Hormone Function & Basal Body Temperature
One of the best-known reasons for checking basal body temperature is to assess for ovulation.
Why is this important?
Around the time of the LH Surge, the body temperature will increase around 1 degree from baseline indicating that ovulation may have occurred.
This can then be used as a reference to determine when to have intercourse if the goal is pregnancy.
So checking basal body temperature can be used as a relatively cheap and effective way if you are trying to conceive.
But does it work all the time?
Each person is unique and their response to both hormones and changes in body temperature is no different.
Some studies (6) show that the body temperature increases as much as 2-3 days prior to or after the LH surge – which can make timing ovulation in these patients difficult.
In a relatively small sample size, as many as 15-20% of patients may experience these changes in response to their body temperature and ovulation.
Does this mean you shouldn’t use the basal body temperature if you are trying to conceive?
It can still be used as a guide, and instead of focusing on intercourse immediately after your raise in body temperature, you can attempt conception 2-3 days before and after (using estimation and history).
This is, of course, assuming other factors (like thyroid hormone and adrenal status) are not interfering with basal body temperature.
As a note, you can also use the combination of basal body temperature + LH strips to help determine when you are most fertile.
How to Use a Basal Thermometer
If you are interested in tracking and taking your basal body temperature for any of the reasons below then I recommend you follow the instructions below.
There are several ways to do it, but by far the most important part is consistency.
That means making sure that you are checking your body temperature at the same time each day while controlling for as many variables as possible.
Also, realize that it is impossible to find a “perfect” thermometer because each will have some faults and there will be SOME inaccuracy no matter how many variables you control for.
Understanding your basal body temperature has more to do with trends than absolute numbers.
For instance, your basal body temperature may only elevate 0.5 degrees during ovulation, but that may be significant for YOUR body – especially if that elevation remains consistent throughout the next 10 days.
How do you take your basal body temperature?
For best results use these guidelines for checking your Basal Body Temperature:
- Keep your basal thermometer RIGHT by your nightstand with a pen and paper
- Check your thermometer (preferably orally) RIGHT upon awakening and before you get out of bed – try to wake up at the same time each and every day
- Write down your results and the time of day that you took the measurement
- Rinse and repeat these steps each and every morning
- Graph your results after 1-2 months of consistent readings to get an idea of thyroid function, adrenal function, and ovulatory status
The goal here is consistency.
That means don’t check your body temperature after you get a glass of water or brush your teeth.
And most importantly:
Keep track of your results!
You can’t make changes if you don’t have the data.
For more information on thyroid status, adrenal status and other FAQ keep reading below:
What is a Basal Body Temperature Thermometer?
A basal thermometer is a thermometer that is more accurate than a regular thermometer and can be used to track your core body temperature.
The information from a basal thermometer can help track ovulation, thyroid, and adrenal status.
It can also be used as a method to assess your general resting energy expenditure or basal metabolic rate which is important for weight loss purposes.
How do you Track Ovulation?
To track ovulation follow the steps outlined above in order to accurately check your basal body temperature.
At the time of ovulation, usually around day 14 (on a 28-day cycle), your body temperature will rise as a result of the LH surge by around 1 degree Fahrenheit.
If you are trying to conceive then this is the time for intercourse as this represents the time of the month when you are most likely to be fertile.
Remember that ovulation does not ALWAYS occur each and every month and other hormones may influence your body temperature, but checking your body temperature can still act as a relatively cheap and efficient way to monitor ovulatory status.
How do you Track Thyroid Hormone treatment?
If you are increasing your dose of thyroid hormone, changing medications, or decreasing your dose you should be tracking your basal body temperature.
As you increase thyroid hormone your basal body temperature should increase.
If your basal body temperature does NOT increase as a result of increasing your thyroid medication then this may serve as an indicator that your body is not converting or not absorbing the medication correctly.
In general, medications that contain T3 thyroid hormone influence your body temperature more than those that contain T4-only medications (Synthroid, levothyroxine, and Tirosint).
How do you monitor Adrenal status?
If you are undergoing treatment for your adrenals then measuring your basal body temperature can help to determine if you are on the right track.
Remember that thyroid hormones, and even sex hormones, influence the body temperature so it’s not 100% accurate, but it still can be helpful.
Body temperatures in adrenal disorders tend to be very chaotic and as treatment occurs the body temperature should become more stable over time.
Generally, these changes take months to be seen, so don’t expect changes within 1-2 months.
The Best basal Thermometer:
I recommend this basal thermometer.
At the end of the day, the exact thermometer doesn’t matter so much as the consistency with which you take your temperature.
The combination of consistency and the general trend of your body temperature, says much more than the digital recording on the thermometer itself.
Now it’s your turn:
Has taking your basal body temperature helped you recover?
Why or why not?
Leave your comments below!