One difficulty of diagnosing and treating hypothyroidism is that many of the standard symptoms are highly variable between individuals, not well-correlated with lab values, difficult to measure, and not unique to hypothyroidism. Doh!

One useful measure seems to be low body temperature. Janie Bowthorpe of Stop the Thyroid Madness has a whole page on body temperature. She writes:

Generally, the average temperature of an adult with a healthy thyroid and a healthy metabolism is 98.6 degrees Fahrenheit or 37.0 degrees Celsius, and that occurs around mid-afternoon or 3 pm. So if you take your mid-afternoon temp and find it in low 98′s or even in the 97′s, you have been given a strong clue that you may be hypothyroid. And a few report their mid-afternoon temp being in the 96′s. BRRRR.

Another temperature clue is to take it before you rise from your bed in the morning. Dr. Broda Barnes, a doctor who paid attention to clinical presentation and prescribed Armour, found that a healthy before-rising morning basal temp should be between 97.8 – 98.2. If it’s higher, you may be hyperthyroid, and if it’s lower, you are most likely hypothyroid. He also recommended under-the-arm temperature testing, but patients have found oral to be just as effective.

Additionally, once you are on natural desiccated thyroid like Armour, and are consistently raising your doses, you will see your temps climb to healthy levels with increasing feel-good symptoms to match. In many patients, reaching 98.6 can happen before you are even on your optimal amount of Armour.

Janie also thinks that fluctuating temperatures can be a sign of adrenal fatigue. That’s a controversial diagnosis, but given the abysmal failure of the standard treatment of T4-only medication for so many people, I’m inclined to side with Janie’s experience.

Dr. Davis also recommends using body temperature in the diagnosis and treatment of hypothyroidism. He writes:

Is there an at-home test you can do to gauge thyroid status?

Yes. Measure your temperature.

Unlike a snake or alligator that relies on the sun or its surroundings to regulate body temperature, you and I can internally regulate temperature. The hypothalamus-pituitary-thyroid glands are the organs involved in thermoregulation, body temperature regulation. While the system can break down anywhere in the sequence, as well as in other organs (e.g., adrenal), the thyroid is the weak link in the chain.

Thus, temperature assessment can serve as a useful gauge of thyroid adequacy. Unfortunately, temperature measurement as a reflection of thyroid function has not been well explored in clinical studies. It has also been subject to a good deal of unscientific discussions.

He recommends taking an oral basal temperature — meaning as soon as you wake up, before you get out of bed or do anything. What temperature are you looking for?

Though there are scant data on the distribution of oral temperatures correlated to thyroid function, we find that the often-suggested cutoff of 97.6 degrees Fahrenheit, or 36.4 C, seems to track well with symptoms and thyroid laboratory evaluation (TSH, free T3, and free T4). In other words, oral temp < 97.6 F correlates well with symptoms of fatigue, cold hands and feet, mental fogginess, along with high LDL cholesterol, all corrected or improved with thyroid replacement and return of temperature to 97.6 F.

Of course, hypothyroidism is not equivalent to low body temperature — any more than it’s equivalent to high TSH. It’s just one sign among many symptoms and signs. And I think it’s a potentially useful sign.

However, I do have some questions about body temperature, some of which Richard Nikoley touched on in this post.

First, what’s the optimal range of body temperature? How much does it vary between persons?

It’s easy enough to determine average temperature in a population: just take a slew of temperatures. Determining optimal temperature is a whole new ball of wax — particularly if many people suffer from undiagnosed hypothyroidism! Plus, the optimal body temperature of a person eating a high-carb vegetarian diet might differ markedly from a person eating a high-fat paleo diet. Similarly, the sedentary person might have a different optimal temperature than the avid crossfitter, marathoner, or weightlifter. And perhaps genetic origins matter too: Inuits might differ from Polynesians. Moreover, perhaps individuals with very similar backgrounds and lifestyles vary in their optimal temperature due to random features of their biology.

In short, knowing the average body temperatures and standard deviations of seemingly healthy people is a far cry from knowing your own optimal body temperature.

Here’s the standard view of normal body temperatures from WebMD:

Most people think of a “normal” body temperature as an oral temperature of 98.6F. This is an average of normal body temperatures. Your temperature may actually be 1°F (0.6°C) or more above or below 98.6F. Also, your normal body temperature changes by as much as 1°F (0.6°C) throughout the day, depending on how active you are and the time of day. Body temperature is very sensitive to hormone levels and may be higher or lower when a woman is ovulating or having her menstrual period.

They also indicate that an oral temperature of less than 96F indicates low body temperature. (I’ve had plenty of temperatures below 96.0 lately, but I’ll post on that separately.)

However, even the standard number of 98.6 is controversial. Here’s a report from Harvard Medical School:

The 98.6° F “normal” benchmark for body temperature comes to us from Dr. Carl Wunderlich, a 19th-century German physician who collected and analyzed over a million armpit temperatures for 25,000 patients. Some of Wunderlich’s observations have stood up over time, but his definition of normal has been debunked, says the April issue of the Harvard Health Letter. A study published years ago in the Journal of the American Medical Association found the average normal temperature for adults to be 98.2°, not 98.6°, and replaced the 100.4° fever mark with fever thresholds based on the time of day.

Now, researchers at Winthrop University Hospital in Mineola, N.Y., have found support for another temperature truism doctors have long recognized: Older people have lower temperatures. In a study of 150 older people with an average age of about 81, they found that the average temperature never reached 98.6°. These findings suggest that even when older people are ill, their body temperature may not reach levels that people recognize as fever. On the other hand, body temperatures that are too low (about 95°) can also be a sign of illness.

The bottom line is that individual variations in body temperature should be taken into account, reports the Harvard Health Letter. Ideally, you and your doctor should have enough temperature measurements at various times of day to establish a baseline for you. Short of this, recognize that 98.6° isn’t the benchmark that we’ve long believed it to be.

So perhaps the best way to know your own optimal body temperature would be to record a series of body temperatures when you feel well with a good-quality thermometer. I wish I’d done that a year ago.

Second, how can a person get precise and accurate measurements of body temperature?

That’s a harder problem than you might think! The article “Temperature measurement in paediatrics has an excellent discussion of the problems with the various methods of measurement. (I’m omitting the citations, as well as some material relevant only to children. You can find that in the article.)

Rectal thermometry: Rectal thermometry has traditionally been considered the gold standard for temperature measurement, but some studies have revealed limitations of this method. Rectal temperatures are slow to change in relation to changing core temperature, and they have been shown to stay elevated well after the patient’s core temperature has begun to fall, and vice versa. Rectal readings are affected by the depth of a measurement, conditions affecting local blood flow and the presence of stool. Rectal perforation has been described, and without proper sterilization techniques, rectal thermometry has the capacity to spread contaminants that are commonly found in stool.

Axillary thermometry: While axillary [armpit] temperature is easy to measure (compared with oral or rectal measurements), it has been found to be an inaccurate estimate of core temperature in children. This type of measurement relies on the thermometer remaining directly in place over the axillary artery, and it is largely influenced by environmental conditions.

Oral thermometry: The sublingual site is easily accessible and reflects the temperature of the lingual arteries. However, oral temperature is easily influenced by the recent ingestion of food or drink and mouth breathing. Oral thermometry relies on the mouth remaining sealed, with the tongue depressed for 3 to 4 min …

The only good news is that (high-quality, properly-functioning) digital thermometers are as accurate as mercury thermometers.

As I said to Richard Nikoley when he e-mailed me that link: “I suppose that the most accurate method is the coroner’s liver temp, but I think I’d rather avoid that!”

As for my own body temperatures, I’ve posted that separately: Body Temperature: Personal Results.