The Thyroid Hormones - T3 & T4

The thyroid is one of the most important glands in the body.  In combination with the brain, the thyroid helps to regulate almost every system in the body!  This is why even minor changes in thyroid functioning can lead to major symptoms in the body. The thyroid works by secreting two major hormones: T3, and T4.  These hormones are named for how many iodine molecules they use when being formed. 

Before we go further, what is a hormone?  Hormones are the messengers that our body uses to communicate with the rest of the body.  When a hormone reaches its destination it changes the way that cells function in that area of the body.  In general, hormones can be made in an active or inactive form.  Whereas the active form can effect change from the moment it is created, the inactive form is exactly as stated, inactive!  Inactive hormones allow the body to store the hormone or to be converted to the active form once it reaches the targeted site. 

So now, back to the thyroid and your T3 and T4 hormones.  Under normal conditions, the thyroid produces 20% and 80% of T3 and T4 hormones respectively. The T3 hormone is the ACTIVE form and the T4 hormone is the INACTIVE form.  Now that we have established what active and inactive hormones mean, we know that most of our circulating thyroid hormone is actually inactive.  This is because, believe it or not, the thyroid is smart!  Because thyroid hormone has such profound effects on the cells of the body, T4 can selectively be converted to its active form in places far from the thyroid.  This process of conversion is aptly named peripheral conversion.  

Thyroid Stimulating Hormone

The hypothalamus portion of the brain regulates the output of thyroid hormones.  The hypothalamus responds to the body’s need for thyroid hormones by secreting Thyroid Stimulating Hormone, otherwise known as TSH.  The job of TSH is to increase the thyroid's production of T3 and T4 therefore TSH can be measured to gauge how well the thyroid is functioning and what kind of stress the thyroid is under.

Usually doctors monitor a thyroid by primarily looking at the TSH levels.  Too high means the thyroid is under active or hypothyroid.  Too low means there is an overactive thyroid or hyperthyroid. 

Thyroid Dysfunction

Thyroid dysfunction occurs when too much or too little thyroid hormones are being produced.  When doctors check thyroid function, this is the first factor that is taken into consideration.

However, many factors can diminish the functioning of the thyroid, these include: mineral and vitamin deficiencies, stress, autoimmune disease and food allergies or intolerances.

Peripheral conversion is also an important and often overlooked part of thyroid functioning.  An easy way to think about it is using the postal service as an analogy.  In order to successfully receive mail, there must be a functioning postal service (T3 and T4 hormones), there must be an address (cells outside of the thyroid) AND you must have a mailbox (the key to getting the hormones INTO the cell)!  When people have difficulty with peripheral conversion its as if they do not have a mailbox.

This is why so many people never solve their thyroid problems.  The conventional model only looks at whether there is enough hormone and not whether the mailboxes are there or open in the periphery.  Conversion from T4 (inactive) to T3 (active) requires a healthy microbiome (good bacteria in gut), minerals, a clean liver and more.  This is what makes naturopathic care so successful at helping those with thyroid issues.

Signs and Symptoms

Hypothyroidism (too little thyroid)

• Fatigue

• Hair Loss

• Sluggishness

• Weight Gain

• Constipation

• Heavy Menses

• Depression

• Sensitivity to cold

• Muscle Weakness

• Dry Skin

Hyperthyroidism (too much thyroid)

• Anxiety

• Changes to menses

• Irritability

• Erectile dysfunction

• Fatigue

• Heavy menses

• Rapid heart beat

• Increased sweating

• Difficulty sleeping

• Diarrhea

• A fine tremor

• Sensitivity to heat

Written by Dr. Erin Sharman, ND

Next issue, look for Thyroid - Beyond the Basics for a naturopathic/holistic view of thyroid dysfunction

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