Like all interacting components of the neuroendocrine system, the thyroid gland and the hormone estrogen are engaged in a carefully-choreographed dance. When the rhythm is right, these two elements interact in a dance that ensures proper functioning of many bodily functions.
The thyroid controls metabolism and body temperature, while estrogen influences fat storage and the development and regulation of the female reproductive system.
Estrogen Dominance in Hormonal Birth Control and Menopause
In some situations, such as with the use of hormonal birth control and in menopause, estrogen levels can become disturbed. This is called estrogen dominance when there is not enough progesterone to properly balance with either low, normal, or high estrogen. Estrogen dominance is characterized by:
- mood swings
as well as
- irregular periods
- heavy bleeding
- ovarian cysts
- vaginal dryness
- poor sleep
- weight gain
Estrogen dominance, or imbalanced estrogen levels, can be harmful to the thyroid; estrogen and thyroid’s dance becomes out of sync. Thyroid function depends on sufficient thyroid hormones circulating in the bloodstream.
Thyroid binding globulin, or TBG, binds to thyroid hormones and carries them through the blood. When TBG is elevated, there is more thyroid hormone bound to it; thus, there is less active thyroid hormone available to perform thyroid functions. When the thyroid cannot perform its dance, symptoms occur, such as:
- weight gain, fatigue
- decreased libido
- poor memory
Estrogen and Increased TBG
Estrogen is known to increase TBG, but it does not raise levels of the hormone that stimulates thyroid, or increase active thyroid hormone. [1, 3, 6, 8, 10, 11]
Research shows that estrogen-containing oral contraceptives can increase TBG and lower active free thyroid hormone. [4, 7, 13]
Hormone replacement therapy (HRT) using estrogen can also cause increases in TBG. [2, 9] The increase of estrogen and TBG disrupts the thyroid and may contribute to autoimmune thyroid disease. 8
Many people depend on estrogen through oral contraceptives or HRT, or naturally have more estrogen than progesterone, as seen in menopause. Research shows that using transdermal methods may be the solution.
Transdermal estrogen therapy doesn’t elevate TBG levels; therefore, it is unlikely that this method would negatively affect thyroid function. 
Balance Sex Hormones and Thyroid Hormones
In summary, the dance of thyroid and estrogen depends on a careful equilibrium of sex hormones and thyroid hormones. Imbalanced estrogen can suppress the thyroid and cause unwanted symptoms such as:
- weight gain
In menopause, this decreased thyroid function due to estrogen can be avoided through use of transdermal estrogen. Assessing the thyroid and sex hormones can help identify imbalances and guide treatment to maintain homeostasis, especially in the delicate dance of the thyroid and estrogen.
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