Is it dangerous to have a suppressed TSH level lower than the "normal" range?
Does a low TSH increase the risk for osteoporosis or heart problems?
Are there situations when having a suppressed TSH is not only safe but helpful?
Are there things that can be done to avoid the potential negative side effects of a low TSH?
I will try to answer these questions and others in this article...
Let's have a quick reminder of what exactly the TSH is and what it indicates.
TSH is short for Thyroid Stimulating Hormone. This hormone is produced by the pituitary gland in the brain. It's purpose is to stimulate the thyroid gland to produce thyroid hormone.
The pituitary gland measures the level of T4 and T3 in the blood of the pituitary and secretes TSH in order to keep the levels of thyroid hormone in the optimal ranges.
When the body is healthy and working normally, this feedback loop works seamlessly to regulate thyroid function in the body.
As a reminder, if there are low levels of T4 and T3 in the pituitary gland, it will increase TSH secretion to try to stimulate the thyroid to produce more thyroid hormone, so the TSH level will rise. Conversely, if there is an excess of T4 or T3, the pituitary will decrease TSH production. The TSH level will drop or sometimes even go to zero.
The result is the TSH moves in the opposite direction of the thyroid hormone level. If you are low in thyroid hormone, your TSH will usually go high, and vice versa.
When looking at a characteristic found in a large population of people, the results will follow a predictable distribution across a graph.
For example, if you graph the heights of everyone in the world, the results will range from as little as 21.5 inches to as tall as 97 inches with the average being about 68 inches. The majority of people in the world will be close to the average height. The further away from the average you go, the fewer people will be that height.
The result is what is commonly called a Bell Curve:
This is also how reference ranges for lab tests are determined.
However, a Bell Curve also assumes that all people included in the graph are equivalent - meaning none are on medication, have different diets, genetic history, etc. which could affect the results.
ZRT is a well-known national laboratory. Their website explains it like this:
Reference ranges do not always reflect a “normal” healthy population free of medications. Most laboratories establish their reference ranges from a large population of people where detailed information on health status, stage of life (premenopausal vs. postmenopausal), and medications and hormones used is unknown, and therefore not taken into account. Couple this with differences in lifestyles, physiology, dietary habits, and genetic heredity, and it’s even more difficult to define, let alone find, a normal population.
This is what happened when the "normal" reference range for TSH was first established. It has since been determined that up to 30% of the people who have a TSH > 3.0 have undiagnosed autoimmune thyroid disease, which skews the TSH results higher than what they would be in a population with no thyroid issues.
So instead of a normal range of TSH ranging from about 0.4-5.0 which it is for most labs, it should instead be about 0.4-2.0.
In other words, even if a patient's TSH comes back at something like 3.5, even before I look at the other lab tests, that signals to me that there is most likely some degree of thyroid dysfunction in that person.
The TSH is an indicator of blood levels of T4 and T3 in the pituitary, which may not be the same as in the rest of the body. This is because the pituitary has a different deoidinase enzyme than the rest of the body.
In this article, I discussed why I believe that the free T3 and reverse T3 levels are much better indicators of thyroid activity at the cellular level than is the TSH.
I recommend trying to get the free T3 > 3.5 and the reverse T3 < 15 if possible. In my experience, that is sometimes very difficult to do in many patients without suppressing the TSH to < 0.4.
So is lowering the TSH < 0.4 dangerous? What if the patient has none of the symptoms of an overactive thyroid (thyrotoxicosis) such as palpitations, tachycardia, insomnia, anxiety, etc.?
What if the free T4 and free T3 levels are in the optimal range even if the TSH is suppressed? Is the low TSH a concern?
The majority of concern about the dangers of lowering the TSH come from studying patients with Grave's Disease. Grave's is an autoimmune disease which results in the overproduction of thyroid hormone which results in a suppressed TSH.
Grave's disease has been shown to result in an elevated serum calcium level due to excessive bone turnover. Untreated, this could ultimately result in significant bone loss and osteoporosis.
Another study, however, showed that in order to get the free T4 level in the optimal range in patients with hypothyroidism, it required them to take a dose of levothyroxine that resulted in a TSH level suppressed below the reference range in over 48% of the patients.
There are actually 2 different instances where suppressing the TSH is not only acceptable but considered the standard of care in conventional medicine:
Both of those groups are good to study to see if any dangerous side effects occurred with long term TSH suppression.
So what does the literature say? Does lowering the TSH with thyroid medication result in the same potentially dangerous side effects that Grave's disease can cause?
Let's look at it further...
This study showed no decrease in bone mass after 1 year in patients receiving suppressive doses of thyroid hormone for treatment of thyroid nodules.
However, this meta-analysis did show a reduction in bone mass in postmenopausal women who received suppressive doses of thyroid hormone for over 9 years. Of note, it did not show the same result in premenopausal women. But this study did not show an increase in bone loss in women with low TSH levels.
In this study, any bone loss associated with prolonged use of thyroid hormone therapy was prevented by the use of estrogen replacement. The use of calcium has also been shown to negate any bone loss caused by thyroid hormone.
Bottom Line? Prolonged suppression of the TSH for years may cause bone loss in postmenopausal women. The amount of bone loss appears to depend on how long they TSH is suppressed and how much it is suppressed. The risk seems to be minimal in premenopausal women.
It also appears that the bone loss can be prevented by using bioidentical hormone replacement and nutrients such as calcium and vitamin D.
So what if the only way you can get your free T3 and free T4 levels to the optimal range is by lowering your TSH < 0.4?
First of all, you need to discuss the pros and cons with your doctor before a decision is made. If you decide to take suppressive doses of thyroid hormone, then the bone loss risk can probably be minimized by also taking bioidentical estrogen, calcium, and vitamin D.
Thyroid hormone definitely has an impact on cardiac function. It helps regulate heart rate, the size of the heart, and the pressure inside the chambers of the heart.
Conditions such as Grave's Disease that cause large increases in thyroid hormone levels have been shown to increase the risk for things such as atrial fibrillation, heart enlargement and heart failure.
So the question becomes, does taking excessive amounts of thyroid hormone result in the same risks as Grave's Disease? At this point, there is not enough data to say yes or no.
So how does thyroid hormone affect the heart?
The heart appears to only respond to T3, yet it is unable to convert T4 to T3 in the cardiac tissues.
It therefore only makes sense that thyroid medications that contain T3 (Cytomel, liothyronine, natural dessicated thyroid) may have more of a cardiac effect than thyroid medications that only contain T4 (Synthroid. Tyrosint, levothyroxine).
If someone has a very healthy T4 to T3 conversion system, they may still get cardiac symptoms from a T4 only medication, but many people have a defect in that conversion.
The risk of excessive thyroid hormone on the heart appears to depend on both how long the TSH is suppressed and how much it is suppressed.
For example, people with a slightly suppressed TSH (subclinical hyperthyroidism) have only mild cardiac issues when compared to Grave's patients.
Fortunately, studies also show that the cardiac abnormalities return to normal once the thyroid level in the body is normalized.
There is also evidence that using beta blockers can prevent and reverse the cardiac changes seen in hyperthyroidism.
Bottom Line? Based on the studies, it appears that suppressing the TSH temporarily will not lead to long term cardiac complications.
Also, if you are taking suppressive doses of thyroid hormone, taking a beta blocker at the same time may actually prevent any cardiac complications from occurring.
There may therefore be situations where taking suppressive doses of thyroid medication for a short time may be beneficial with minimal risk. However, it should only be considered after consulting with a doctor with experience in thyroid management.
I had a patient ask me recently, "If the TSH is not an accurate measure of thyroid levels in the cells of the body, why even check it?"
That is a fair question, but the fact is, monitoring the TSH is still considered standard of care for managing the thyroid. The TSH should therefore be monitored, just not by itself.
The whole picture of the thyroid should be evaluated by monitoring the complete thyroid panel which also includes the free T4, free T3, reverse T3, and thyroid antibody levels.
If your doctor is not checking all of these labs when testing or monitoring your thyroid function, you are not getting a complete picture of what is going on with your thyroid.
Read this article if you want to know more about each of these lab tests, what they mean, and optimal ranges of each.
It is important to monitor your TSH level as part of your thyroid hormone management, but it is even more important to monitor all of the tests in a complete thyroid panel.
Taking enough thyroid hormone to lower your TSH level below the normal reference range may have some potential long term consequences. Fortunately, most of those can be avoided if your thyroid levels are closely monitored and managed properly.
It may require taking suppressive doses of thyroid hormone temporarily in some patients in order to get their free T4 and free T3 levels into the optimal ranges. In those instances, it is extremely important to monitor bone density and cardiac health.
In many cases, the bone loss may be prevented by also taking bio-identical estrogen and calcium.
Many of the cardiac issues may be prevented by also taking a beta-blocker.
As a general rule, taking enough thyroid hormone to suppress the TSH should be avoided in postmenopausal women, whereas the risk does not appear to be as high in premenopausal women and in men.
Now it's your turn...
Have you even taking enough thyroid hormone to suppress your TSH?
Did you have any negative side effects?
Do you currently have a TSH in the normal range, yet you still have symptoms of low thyroid?
Leave your questions or comments below.
Dr. Whelchel is a family physician who specializes in functional medicine, especially hormone optimization. He has over 20 years experience in private practice managing patients with various medical issues. His passion is helping patients reach their full potential of wellness and quality of life. He grew up in the Texas Panhandle where he currently lives. He is married and has 3 awesome children.