One of the many pieces to the thyroid dilemma includes the balance of other hormones. Particularly in females with the balance of estradiol (also known as E2, the most potent form of estrogen) and progesterone. You may have remembered way back to the introductory article, or the article explaining how the liver can affect your thyroid physiology, a mention of a specific protein that binds thyroid hormone called thyroid binding globulin. This protein acts in a similar scenario to goldilocks and the three bears, you want thyroid binding globulin to be not too high or too low. If it’s too low, you can have too much free thyroid hormone which can lead to thyroid resistance. If it’s too high, it acts as a ball-and-chain in which thyroid hormone is bound and can’t enter the cell. Just like how goldilocks likes her porridge, you want thyroid binding globulin to be “just right.” We will come back to this later in this article.
The sea of estrogenIn today’s day and age, we are swimming in a sea of estrogen. Estrogen-like compounds such as: Atrazine, BPA, Dioxins, PBB, PCBs, Phthalates, and many more. These compounds are literally everywhere, and are next to impossible to avoid. They are in the air, the water, our food, our utensils, plastics, receipts and cosmetics. The group of individuals this effects most is developing infants and children. One study says that growing children are so sensitive to estrogens that they can respond with increased breast development at serum levels below the current detection limits. (1) It is without question and reasonable to believe that environmental estrogens are playing a role in the steady decline of the age of puberty. One study done in 2012 found that 30% of girls will enter puberty (determined by increased breast growth) around age eight(2). The changes that are occurring from exogenous sources of estrogen are becoming more and more prevalent. This is not even mentioning the sheer amount of changes to hormones females are willing to use, such as hormone replacement therapy and birth control/oral contraceptives. The prevalence of birth control prescriptions is staggering. Around 98% of US women have used some form of contraception during their lives (3). As with anything in the body, you cannot compartmentalize one system in the body. You alter your sex hormones, other systems are going to be affected-especially your thyroid hormone.
Estrogen and Thyroid Binding Globulin
Estrogen, has been shown to increase the production of thyroid binding globulin from the liver (4,5). Some studies states that elevated estrogen can increase thyroid binding globulin by the liver over 2 – 3 fold (6). It is no wonder why the United States is riddled with thyroid as well as reproductive related issues. In animal studies, compounds from soy which mimic estrogen have been shown to competitively inhibit thyroid hormone synthesis via thyroid peroxidase enzyme (7,8).
Progesterone and Estrogen – A Balancing Act
Progesterone has been shown to oppose estrogen receptors (9). Since estrogen seems to decrease thyroid hormone production and increase thyroid hormone binding, it makes sense that in certain studies they found that when subjects who when on progesterone showed increases in their circulating levels of Free T4 (10). If estrogens were like the little crazy children running around, progesterone is like the parents who watch over the children. When you have not enough parents watching the kids, one of them breaks free and can cause problems. Too much unopposed estrogen tends to cause not only problems in thyroid physiology, but proliferation of tissues which can increase the risk for cancers. This is why it is important to check the balance of these hormones in every patient who has thyroid related dysfunction. If you suspect you may have a problem with your hormone levels, please do not try and fix this alone. Find a good practitioner who will help. If you do have to use estrogen for hormone replacement therapy it seems that the transdermal delivery is a better choice for not raising thyroid binding globulin levels (4,5).
What About Male Hormones and Thyroid Function?
Yes, testosterone can impact thyroid physiology too in both males and females. A decrease in testosterone in males, results in a decrease in the available tissue T3 without the subsequent rise in TSH (11). This implies a decrease in the ability for thyroid hormones to enter the cells, as well as a decrease in the sensitivity between the hypothalamic pituitary thyroidal axis. Generally, testosterone tends to decrease thyroid binding globulin (5). So females with elevated androgens, like those with polycystic ovarian syndrome or those with insulin resistance have a greater susceptibility to thyroid hormone resistance.
Sex Hormone Binding Globulin (SHBG) – A Unique Way to Measure Thyroid Hormone Resistance
When estrogen and thyroid hormone get into liver cells, the liver tends to produce more sex hormone binding globulin (note this is different than Thyroid Binding globulin). It is a normal response to see an elevation in SHBG with both estrogen and thyroid hormone. Dr. Kent Holtorf who has done extensive research on the thyroid and how it gets used inside of the cell (12), suggests-if estrogen levels are normal and you don’t see a rise in SHBG when given thyroid hormone that it is indicative of thyroid hormone resistance.
If you are one who has been trying to find answers to your thyroid problems, it is important to find a functional medicine practitioner who can run the necessary tests to better address the root problem. Many things can impact healthy thyroid function, and sex hormones like: estrogen, progesterone, and testosterone are just a few of them.