It’s estimated that 10% of the North American population is afflicted by a thyroid condition, and for post-menopausal women the number goes up to 20%! And just like all other hormones, thyroid hormone levels are influenced by other hormones, such as progesterone and cortisol, so it plays a very important role in female hormone balance.
The thyroid gland is a butterfly shaped gland at the base of our throat that is responsible for maintaining our metabolism (among other things). It gets a signal from the brain (Thyroid Stimulating Hormone – TSH) and then releases thyroid hormone in the form of mostly thyroxine (T4) and a little bit of triiodothyronine (T3). The T4 then loops back up to the brain to say “okay got the message, we’re making thyroid hormone down here so you can stop sending the signal”. That way the TSH level stays pretty normal. If for some reason the thyroid isn’t secreting T4, then the brain doesn’t get the message and sends the TSH signal a little bit louder. So if your TSH levels are very high, it means that your thyroid hormone isn’t being secreted. So high TSH means low thyroid hormone.
Now lets move on to the different types of thyroid hormone. The thyroid produces both T4 and T3, and about 5-10x the amount of T4 than T3, even though T3 is much more biologically active than its more prevalent counterpart (T3 is 3 to 4 times more potent than T4). Only 20% of circulating T3 is secreted by the thyroid; the remainder is produced by altering T4 in the liver, kidney, and other peripheral tissues (requiring selenium).
I like to look at this like the thyroid is a parent of millions of kids (our cells). The thyroid makes each kid/cell a PB&J sandwich, and then leaves a ton of bread on the counter so that if they want any more, they can butter their own bread as they get hungry. In this way the thyroid knows every cell has been fed, but also recognizes that each cell is different, and has different requirements at different times.
The Role of the Liver
As a major portion of the peripheral conversion of T4 to the active form T3 occurs in the liver, any liver insufficiency may reduce the amount of circulating active thyroid hormone. In addition, 75% of T4 circulates bound to thyroxine-binding globulin (TBG), with much of the remaining T4 bound to other carrier molecules leaving only a very small amount (less than 0.01%) to circulate in an unbound state. Only hormones that are in an unbound state can have activity in our bodies. Therefore, anything that might change the amount of TBG, will also alter the fraction of free T4 available for use by the cells. There are many drugs, hormones and other substances that can impact TBG. TBG is produced in the liver, so this is yet another situation where the liver can impact hormonal function.
What is reverse T3?
T4 can also be converted into reverse T3, which is not only another inactive form of thyroid hormone, but actually inhibits T3 formation by blocking the enzyme that is required for T3 formation (WTS).
Stress & Cortisol
Cortisol is our stress hormone, which is secreted and allows us to perform under pressure (be that running from a predator or submitting a report on time). Unfortunately, it can suppress thyrotropin secretion by the pituitary, the signal from our brain to our thyroid telling it to make more hormone (Rundsarah & Baha).
Also, the enzyme that converts T4 to T3 is negatively impacted by stress, fasting and illness. So ensuring that your stress level stays low is an important aspect for getting your thyroid back into balance.
Progesterone makes thyroid receptors more sensitive to thyroid hormone. So when we miss an ovulation (whether that be due to menstrual cycle irregularity or full-blown menopause), our level of progesterone drops, meaning that so does its supportive role for our thyroid hormone. Not only that, but when we miss ovulations we end up with a relative estrogen dominance. When estrogen and progesterone are not in balance, unopposed estrogen increases the amount of thyroid binding globulin (TBG) in the blood, making a percentage of the circulating thyroid hormone unavailable. It does so by making the liver sluggish, and reducing clearance of TBG by the liver.
Oral estrogen administration to hypothyroid women who were chronically treated with thyroid hormone (Synthroid for example) caused a decrease in thyroxine levels and a simultaneous increase in TSH levels, meaning it makes them more hypothyroid (Rundsarah & Baha). So taking oral birth control is creating an estrogen dominant state that can inhibit thyroid function and may lead to weight gain, fatigue and other symptoms.
Progesterone on the other hand decreases TBG allowing for more active thyroid hormone in circulation. Futhermore, thyroid hormone also helps convert pregnenolone to progesterone (Bhattacharrya, et al), as well as supports progesterone release from the ovary (Datta et al). So not only is progesterone helping boost thyroid levels, but thyroid hormone also boosts progesterone!
Thyroid panel: TSH, T3, T4, rT3, TPO, TRH
If you go to your family doctor to get your thyroid tested they will likely do a physical exam which will include feeling your neck for bumps and adhesions, and they will probably also do a blood test for Thyroid Stimulating Hormone (TSH). If the TSH comes back as abnormal, they will then potentially test for T4. Now remember, T4 is not the more active form of thyroid hormone, so it’s not the best marker of thyroid function. That being said, if your T4 and TSH are off and if you have symptoms of hypothyroidism, you will probably be given a prescription for artificial T4 (Synthroid or Levothyroxine usually). For many people this will medically correct the deficiency (though not the root cause because why did the thyroid fail in the first place?) and they’ll start feeling better. If you are still not feeling better after the prescription, then it’s possible that your problem more relates to your ability to convert the T4 to the more active T3. We’ll talk more about this in the treatment section, but testing your T3 levels might be the next step. It also might be valuable to test your reverse T3 and your thyroid antibodies to see if there is an autoimmune component that needs to be addressed. It’s also possible to test your Thyrotropin Releasing Hormone (TRH) to determine if the problem stems from the brain level (but this is rare).
Below is a list of important items to be sure are in line for optimal thyroid health:
- Synthroid and Levothroxine are T4, the inactive form of thyroid hormone, so if part of your issue is the inability to efficiently convert T4 to T3, though your TSH level might improve with medication, the actual thyroid function may not. There are other medications out there that are either straight T3 (though you often have to take them multiple times per day, so are more inconvenient), a combination of T3 and T4, or you can get dessicated thyroid hormone which has everything a thyroid would need (though are usually of non-organic animal source).
- Iodine is a nutrient that is very important for thyroid hormone production, and is not easily found in our diets. The average iodine intake in the United States has decreased by approximately 50% between the 1970s and the 1990s (Kliegman). You can either supplement directly (though it is a volatile nutrient and too much can be dangerous, so doing so under supervision is advised) or it can be found in iodized salt or seaweeds. My preferred method is to eat about 2 tbsp or 1 sheet of nori per day.
- Iodine is a halogen (on the periodic table of elements), so other halogens can look very similar to our receptors and block iodine activity. So be mindful to avoid chlorines (in municipal water, salt), fluorine (in toothpaste and municipal water) and bromine (found in wheat and some citrus flavoured drinks). If you are iodine deficient then you become more susceptible to iodine suppressing activity of foods such as soy and cruciferous veggies (but if you have normal iodine levels then these are usually healthy food choices!)
- For more information on iodine read this detailed article by Dr. Flechas, MD.
- Tyrosine is an amino acid required for thyroid hormone synthesis, and the typical dose is between 500-1500mg per day.
- Several trace minerals and vitamins are required as well including zinc, selenium, iron and the B vitamins. You can either supplement with these, or ideally eat a diet rich in veggies and nuts and should give you adequate amounts in a natural form.
- Selenium prevents production of rT3, so it’s particularly important!
- Fat soluble vitamins D, E and A are of value for your thyroid function as well, and therefore it’s necessary to have proper function of your liver and gallbladder to secrete adequate amounts of bile for fat absorption. Vitamin D is often low in northern climates, and though it’s usually safe to supplement with 1000-2000IU per day, I prefer to do the blood work to assess the baseline levels, as vitamin D can also be dangerous in high levels.
- Gut health is important to ensure nutrients are being absorbed. Towards the end of our first visit together I’ll break down my patient’s case into a list of issues that need to be improved. Often my list will be a lot longer than what my patient came in for, but we almost always agree on the longer list and proceed from there. One item that people often overlook is their digestion. They may have simply adapted to manage their daily constipation or loose stool issue, and no longer see it as a problem. They view digestion as a lifestyle inconvenience. In reality, digestion is probably the most important health issue for all of us. If we’re not properly digesting our food, then we’re not acquiring those valuable nutrients integral to the proper operations of our bodies. If you’re not absorbing the iodine, zine, selenium etc that your thyroid needs to make active thyroid hormone, then you can medicate until the cows come home with artificial thyroid hormone, and your cells still won’t benefit.
- Though a sensitivity to any food can be detrimental, gluten and dairy antibodies have been often seen in those with hypothyroidism, and in particular, celiac’s disease is often found concurrently with thyroid disease. A gluten and dairy free dietary experiment for 3 weeks won’t hurt, so it’s worth trying it out and seeing if you feel a bit better.
- Due to the close relationship between the adrenals and the thyroid, improving adrenal health is vital for returning the body’s hormone to balance. Often in practice I need only prescribe dietary seaweed and support the adrenal glands, and the thyroid rebalances on its own. We might also need to balance female hormones to be sure ovulation occurs for proper pairing of progesterone with thyroid hormone.