Your Basal Body Temperature Can Be An Effective Test For Measuring Thyroid Function

Why Take Your Basal Body Temperature To Measure Your Thyroid Function?

So, what is "basal body temperature", or BBT all about anyway? Could this really be a worthwhile thyroid test for hypothyroidism or hypothyroidism type 2 - otherwise known as an underactive thyroid?

This test is used to detect how well your thyroid is doing – beyond what regular blood tests like TSH (thyroid stimulating hormone); FT3 (free T3 hormone) or FT4 may have shown.

How Medicine Normally Assesses Thyroid Function

Usually, medicine will diagnose thyroid disease by testing for TSH levels, or the amount of T3 and T4 hormone in the blood. Bring back to mind, however, that T3 is the primary hormone which helps regulate body temperature – not T4!

Hence, if - despite adequate secretion of T4 by the thyroid gland - we’re not getting sufficient conversion of T4 to T3, or T3 is unable to activate cellular receptor sites, then the basal body temperature, or BBT will be found to be low – as will thyroid function.

Want To Skip Ahead In This 'Hypothyroidism – Basal Body Temperature’ Discussion?

The following ideas will obviously flow more logically if you read it as it unfolds below, however, if you're in a hurry and wish to focus on one specific point initially, then simply click on any of the links in the blue box, directly below, in order to jump ahead.

Body Temperature Is A Major Indicator Of Thyroid Status
Low Body Temperature = Poor Thyroid Function
Why Does Body Temperature Need To Be At 37 Degrees Celsius?
Thyroid Testing Via Blood Alone Can Result In Misleading Conclusions
How A Miss-Diagnosis Can Result In A Wrong Prescription
How To Take Your Basal Body Temperature - BBT
Why Only Use The Old-Fashioned Mercury Thermometer?
Why Re-Set Your Mercury Thermometer The Night Before?
This Test Is Taken Under-Arm – Not Under-Tongue
Special Instructions For Menstruating Women Doing This Test
Interpreting Your Body Temperature Test
Celsius To Fahrenheit Conversion Formula


Body Temperature Is A Major Indicator Of Thyroid Status

By using the fact that the thyroid hormone, T3, helps keep our bodies warm, an effective form of thyroid testing can therefore be achieved by working backwards, and tracking basal body temperature via the use of a basal body thermometer.

In other words, using your body basal temperature provides us with a more realistic understanding of how efficiently your thyroid gland is actually functioning – compared to thyroid testing, done on a blood sample, which only measures how much hormone is present in that specific amount of blood – not how active it is.

Consequently, measuring your basal body temperature makes it possible to achieve a far more authentic way of testing for true thyroid function. It's based on the simple, yet scientific premise that in a sense, your thyroid is much like the thermostat in your air-conditioned home.

As you know, this little device keeps track of how cold or warm it is inside your house, and aims to maintain precisely the temperature you have chosen to be most comfortable for you. Similarly, a healthy thyroid will keep your body/'house' at a steady temperature, despite temperature fluctuations within your external environment.

Low Basal Body Temperature = Poor Thyroid Function

As your thyroid starts to fail in this major function of maintaining body temperature, it's no longer able to keep your body warm at a constant level, and you'll find your temperature becoming persistently lower.

A healthy human's normal body temperature is 37 degrees Celsius (98.6 Fahrenheit).

However, way back when I was a nurse, 30+ years ago, I remember being astounded by how many hospital patients would inevitably record a much lower temperature than that. Anywhere from the high 35's to the low 36 degrees Celsius.

I once remarked upon this to one of the doctors, whose response was that this is 'normal', because: 'everyone seems to present with less than 37 degrees nowadays'.

Interesting perspective... but very unscientific! Just because huge numbers of people – note: particularly ill people in hospital! – present with a certain clinical reading doesn't then mean that this is a 'normal' situation, let alone representative of a healthy population outside the hospital.


Why Does Body Temperature Need To Be At 37 Degrees Celsius?

Briefly, every metabolic function in your entire body is completely dependent on enzyme function. In turn, enzyme function is highly dependent on temperature.

Therefore, if your basal body temperature is below normal, then all enzymes in every cell of your body will be working below par, which in turn can have a profound effect on how efficiently your cells - and hence your entire body – are able to function.

It's actually as simple – and fundamental - as that. A chronically low, basal body temperature equals poor body function, which in turn can end up causing a huge number of symptoms.

Thyroid Testing Via Blood Alone Can Result In Misleading Conclusions

The problem is that using the 'normal' thyroid testing with which to measure function of the thyroid gland, and done via a blood sample, is in fact quite insensitive, plus the medical interpretation is also far too 'coarse'.

End result? Many people suffering from a genuinely under-functioning (compared to mal-functioning) thyroid will not be picked up by the current medical diagnostic system.

This can have both sad, as well as grave repercussions, since people suffering from very real symptoms are fobbed off as 'imagining' their un-wellness, or worse, are prescribed completely inappropriate drugs for their symptoms.


How A Miss-Diagnosis Can Result In A Wrong Prescription

Let's take just one example of this type of situation. One common symptom many people with an underactive thyroid may experience is depression. The problem is that if your doctor isn't able to 'connect the dots' between your unhappiness and your thyroid - because the blood tests keep saying everything is 'normal' - then that doctor is probably going to prescribe anti-depressants.

However, as you can see in this example, the primary reason for this patient's depression may well be a form of hypothyroidism – for which anti-depressants are not really the most appropriate treatment, as they don't treat the fundamental cause driving that depression.

Anti-depressant therapy may well help that person feel better, but as it is not dealing with the source of the problem, it most likely means such a person with depression may need to stay on anti-depressants for a long time.

Therefore, in order to get rid of that 'depression' on a fundamental level, would also necessitate the correct thyroid support therapy. As that person's thyroid function subsequently comes back to true-normal, so will their 'depression' in most cases simply melt away.

Dr. Broda Barnes (ref.1) was one of the pioneers who explored this major health issue of subclinical hypothyroidism, and who used what was called the 'Basal Metabolic Temperature Test' for diagnosing such cases.

Despite its seeming simplicity, this genuinely relevant diagnostic technique is capable of identifying many people who otherwise would 'fall between the cracks', because they did not show up as being hypothyroid via 'regular' blood tests.

How To Take Your Basal Body Temperature - BBT

This BBT thyroid test is quite simple, and is to some extent standardized by being performed first thing in the morning, upon awakening, and before you become physically active. Tracking basal body temperature over at least 3 mornings also gives you a better average to work from.


Why Only Use The Old-Fashioned Mercury Thermometer?

Unfortunately, most digital basal thermometers on the market are not accurate enough for this form of thyroid testing, whereby we are using your body basal temperature. A digital thermometer, and even an infrared thermometer inevitably under-records a person's body temperature, which in turn would lead to an over diagnosing of the type of subclinical hypothyroidism we're discussing here.

So, what we need to use instead is the old-fashioned mercury thermometer, around which this specific temperature test was originally created and standardized. These type of thermometers can still be found in many chemists/pharmacies, and are not particularly expensive. Another way of finding this style of mercury thermometer is to ask for a mercury-based fertility thermometer.

These are used during a woman's menstrual cycle; the results then plotted on a fertility chart, thus allowing her to establish the time of her ovulation, and therefore when she is most likely to be fertile.

Once again, please understand that the modern, digital-style of thermometers are calibrated differently from the mercury type, hence will give inaccurate readings for this particular test. Do ensure you only use the old-fashioned mercury thermometer.

Why Re-Set Your Mercury Thermometer The Night Before?

In the name of standardizing this test, it is not only important to use the mercury thermometer, but it is equally imperative that this style of thermometer is re-set, or primed, by shaking it down the night before the first morning test, as well as after you have recorded each morning's result. This ensures the thermometer is ready to use well before the next testing.

Bringing up these points is vital, because it takes quite a bit of shaking to get that mercury column to go down to below the 35 degrees Celsius (95.0 degrees Fahrenheit) figure on this style of thermometer.

Remember, however, that any physical activity will activate your metabolic rate... and hence increase your temperature, thus preventing you getting the required basal reading.


This Test Is Taken Under-Arm – Not Under-Tongue

As soon as you wake up, take your temperature, underarm, for a full 10 minutes. It is imperative to place the old-fashioned mercury thermometer underarm, and not under the tongue. It is also crucial for you to not move or get out of bed for any reason before taking the temperature. Such activity will only raise your basal body temperature, and make the test useless.

It is also best if you can gently push back most of your blankets before doing this test. To get a better average result, you're encouraged to do this test for at least 3 consecutive mornings – if possible. However, one or two skipped mornings usually doesn't matter.

Special Instructions For Menstruating Women Doing This Test

For a women who is having her menstruation, it's important to only take the temperature on the 2nd, 3rd & 4th morning of their period. In other words, if their period starts today, then tomorrow is considered the 2nd morning.

For men and non-menstruating women, the temperature can be taken on any 3 – or more - consecutive mornings.

Once you have recorded the 3 or more readings, work out the average temperature.

Interpreting Your Basal Body Temperature Test

Yet again, a genuinely normal body temperature in a healthy human being is 37 degrees Celsius (98.6 degrees Fahrenheit). If the average basal body temperature reading is below 36.5 degrees Celsius (97.7 degrees Fahrenheit), then this is regarded as - not an absolute – but definitely a good indication, along with a thorough consideration of a person's symptom profile, that they have an underactive thyroid.

The more the average temperature is below 36.5 degrees Celsius (97.7 degrees Fahrenheit), the more the thyroid is under-functioning. Any average temperature below 36.0 degrees Celsius, (96.8 degrees Fahrenheit) would suggest that the thyroid is starting to go into significant mal-function.

In such cases, a TSH reading (done on a blood sample) is also more likely to come back as 2.0 mU/L or higher.

It's important to accurately record the readings, as well as try to have those readings taken at about the same time each morning – as much as possible. An average reading of less than 36.5 degrees Celsius does strongly indicate an underactive thyroid, otherwise known as 'sluggish thyroid'; 'thyroid resistance', or what Dr. Starr termed as hypothyroidism type 2.

The greater the temperature is found to be below 36.5 (97.7 degrees Fahrenheit), the more the thyroid can be regarded as incapacitated, or not functioning at an optimal level.


Celsius To Fahrenheit Conversion Formula

The conversion formula for changing a reading from Celsius to Fahrenheit is:

°F = (9/5 °C)+ 32°

For example:

Converting 36.5 degrees Celsius to Fahrenheit:

1) 36.5 x 9 = 328.5

2) 328 divided by 5 = 65.7

3) 65.7 + 32 = 97.7


1) Barnes, Broda, MD, Galton, Lawrence, Hypothyroidism – the unsuspected illness, Harper & Row. NY. 1976. ISBN: 0-690-01029-X

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