Hypothyroidism – A Female Problem
Hypothyroidism affects women seven times more frequently than men. The higher incidence of genetically inherited autoimmune thyroiditis among women is one reason why. The effect of female hormonal imbalance is another.
The menstrual cycle is characterized by changing ratios of the female hormones estrogen and progesterone. During the first half of the cycle estrogen dominates, and during the second half progesterone dominates. However, as the ovaries age, women produce decreasing amounts of progesterone, resulting in a condition called estrogen dominance.
Estrogen dominance causes the liver to produce increasing levels of thyroid-binding globulin (TBG), a protein that has a strong attraction to circulating thyroid hormones. When TBG latches onto a thyroid hormone, the hormone is no longer free to enter into the cells and be used for metabolic reactions.
Even in the most ideal of circumstances, only 0.05 percent of thyroid hormone circulating in the bloodstream—a mere five parts in ten thousand—remains unbound and available to the cells. The remainder—a full 99.95 percent—is bound to TBG and other proteins in the blood. In women with estrogen dominance, the situation is even worse, due to the higher levels of TBG that are produced by the liver.
Birth control pills, pregnancy, and postmenopausal estrogen supplementation also increase levels of TBG, compounding the problem for women. In contrast, the male hormone testosterone has no effect on TBG and actually stimulates the conversion of the inactive thyroid hormone, T4, to the active thyroid hormone, T3, within the cells. It’s no mystery why women are much more likely than men to experience low thyroid function.
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