Can Too Much Exercise Trigger Thyroid Autoimmunity?

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There is no question that engaging in regular exercise is important.  Exercise has many benefits, as it can decrease the risk of developing cardiovascular disease, improve insulin sensitivity, increase bone density, etc.  However, while many people don’t exercise enough, there are some people who exercise excessively, which also isn’t a good thing.  As I’ll discuss in this post, too much strenuous exercise can have a negative effect on the immune system and might potentially be a factor in the development of an autoimmune thyroid condition such as Graves’ Disease or Hashimoto’s Thyroiditis.

Although the focus of this post will be on the risks of overtraining in those with autoimmune thyroid conditions, moderate exercise seems to offer a protective effect on the immune system (1).  For example, while strenuous exercise can theoretically make someone more susceptible to an upper respiratory tract infection by temporarily suppressing the immune system defenses, moderate exercise can actually protect against upper respiratory infections (2).  Exercise has effects on both the humoral and the cellular immune system (2).

What Are The Potential Consequences Of Excessive Exercise?

Although there are no studies confirming that excessive exercise causes thyroid autoimmunity, there is no question that overtraining does affect the cytokines of the immune system.  And as I have discussed in other articles, these cytokines play a role in different autoimmune conditions, including Graves’ Disease and Hashimoto’s Thyroiditis.  In a properly functioning immune system you ideally want to have a healthy balance between T-helper 1 (Th1) and T-helper 2 (Th2) activity.  But certain factors can affect these pathways, and make someone Th1 or Th2 dominant.  This in turn can increase the chances of the person developing either Graves’ Disease or Hashimoto’s Thyroiditis.

Most cases of Hashimoto’s Thyroiditis are Th1 dominant conditions, whereas most cases of Graves’ Disease are Th2 dominant conditions.  However, this isn’t always the case, and the only way to know for certain is to test the cytokines.  A few years ago such testing was more common, as some natural healthcare professionals would test the cytokines through the blood to determine if someone was Th1 or Th2 dominant and then they would recommend specific nutrients or herbs to balance these pathways.  Although some healthcare professionals continue to do such testing on their patients, this remains controversial, and isn’t as commonly practiced these days.

So how does exercise specifically affect the cytokines and the Th1/Th2 balance?  Well, exercise of moderate intensity seems to cause a slight shift towards a Th1 profile, thus reducing inflammation and reducing the risk of infections (3).  However, it appears that acute exercise, as well as chronic moderate exercise, shifts the immune response towards a Th2 profile (3) (4).  Prolonged intense exercise may shift the balance towards Th2 to an even greater extent (3) (4).

What this is saying is that short bouts of intense exercise and chronic moderate exercise slightly shifts the immune response towards a Th2 profile, and excessive exercise seems to shift the immune system balance too much towards Th2.  Since most cases of Graves’ Disease are Th2 dominant conditions, this would suggest that excessive exercise can potentially trigger Graves’ Disease in those people who have a genetic predisposition for this condition.  However, the Th1 immune response offers protection against pathogens (i.e. viruses), and so this shift towards Th2 can make the person more susceptible to an infection, which can be a factor with either Graves’ Disease or Hashimoto’s Thyroiditis.  So excessive exercise might trigger Graves’ Disease by shifting the person to a Th2 dominant state, but it also might indirectly lead to Hashimoto’s Thyroiditis by making the person more susceptible to viruses and other infections.  For example, if someone with a genetic predisposition to Hashimoto’s exercises excessively this can weaken their immune system defenses, making them more susceptible to an infection, which in turn can lead to the development of Hashimoto’s Thyroiditis.

More About Excessive Exercise and Infections

Since infections can play a role in the development of autoimmune thyroid conditions I’d like to further discuss how excessive exercise can make someone more susceptible to developing an infection.  Secretory IgA plays an important role in providing protection by binding to pathogens, including viruses (5).  In other words, it is a first line of defense against pathogens.  However, prolonged strenuous exercise can cause a decrease in secretory IgA (6), which in turn can increase the chances of the person developing an infection.

So there are two mechanisms in which overtraining can increase the risk of developing an infection, which in turn can trigger autoimmunity.  The Th1 pathway is important to help prevent someone from getting an infection, but excessive exercise can shift the immune system towards a Th2 dominant state, which will make someone more susceptible to developing an infection.  In addition, excessive exercise can also lead to a decrease in secretory IgA, which plays a big role in providing protection against pathogens, including viruses.

The Impact Of Excessive Exercise On The Cardiovascular System

Although the focus of this post is on the risks that excessive exercise can have on the immune system, and how it can potentially trigger an autoimmune thyroid condition, there are other risks of overtraining as well.  Although there is no question that moderate cardiovascular exercise has some great health benefits, and that high intensity interval training can also be beneficial, too much exercise can cause harm to the cardiovascular system.  Excessive exercise can cause oxidative stress and increase the risk of atrial fibrillation, coronary artery disease, and malignant ventricular arrhythmias (7) (8).  So while it’s important to exercise regularly, you don’t want to overdo it.

Overtraining and Adrenal Insufficiency

The chronic stress that results from overtraining can also cause problems with the adrenal glands, and can even lead to adrenal insufficiency in some cases (9).  However, it appears that excessive exercise alone isn’t the only factor, as in order for adrenal insufficiency to develop it takes a combination of chronic overtraining along with a triggering stressful event (9).  But of course many people deal with a great amount of stress in their lives, and sometimes they use excessive exercise as a way of managing their stress.  In other words, someone who is dealing with a great amount of stress might initially feel better when overtraining, not realizing that they are actually worsening their health.

How Much Exercise Is Too Much?

The question you might have at this point is “how much exercise is considered to be too much?”  Well, further research is still needed in this area, but if you are engaging in moderate aerobic activity then you should be able to hold a conversation while exercising.  However, you might not be able to hold a conversation while engaging in high intensity interval training, although you shouldn’t be working out at a very high intensity for longer than a few minutes consecutively.  Just as a reminder, high intensity interval training involves short bouts (i.e. 30 seconds to a few minutes) of high-intensity exercise separated by one to five minutes of recovery (which involves either no or low intensity exercise).  Although doing this is fine in most healthy individuals, if someone participates in continuous high intensity exercise for prolonged periods of time (i.e. five minutes or greater) then this will increase the risk of causing problems with the immune system, cardiovascular system, and possibly other areas as well.

In addition, if you have a condition such as Graves’ Disease or Hashimoto’s Thyroiditis then you probably need to be extra cautious about overtraining, and in some cases even engaging in moderate exercise can cause problems.  For example, if someone has Graves’ Disease and has an elevated heart rate, then they need to be very cautious when doing any type of cardiovascular exercise.  This might seem obvious to many people, but I have worked with patients who had an elevated heart rate who asked if it was okay to engage in high intensity aerobic exercise a few days per week.  On the other hand, while someone with Hashimoto’s Thyroiditis might not need to worry about an elevated heart rate, if they have compromised adrenals then they will want to be cautious about engaging in vigorous exercise, even if they aren’t overtraining.  I mentioned earlier how someone who engages in excessive exercise and deals with a high amount of stress has a greater risk of developing adrenal insufficiency, and so it shouldn’t be surprising that someone who already has compromised adrenals will be doing more harm than good by overtraining.

In summary, while exercising on a regular basis is important and can provide many health benefits, exercising too much can do more harm than good.  With regards to the immune system, excessive exercise can cause an imbalance of the cytokines and decrease secretory IgA, which can increase the risk of developing either Graves’ Disease or Hashimoto’s Thyroiditis.  In addition, overtraining can have a negative impact on cardiovascular health, as well as the adrenals.  And so you need to be very cautious about exercising too much, and this is especially true if you have an autoimmune thyroid condition.