My View on Your Hormones

Interaction between Thyroid Function and Sex Hormones

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Normal thyroid function is important for the normal sexual function of the gonads.

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Thyroid hormones have direct effects on the ovaries, testes and corpora cavernosa through specific receptors on the cell nucleus. Additionally, thyroid hormones influence the production of estrogen, progesterone and testosterone. T4 affects the maturation of female eggs and T3 supports the ovulation of the mature egg. Both hypothyroidism and hyperthyroidism can significantly impair fertility.

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Thyroid hormones also have indirect effects on the gonads through the interaction with and the influence of the hypothalamus-pituitary-thyroid axis and the hypothalamus-pituitary-gonad axis. Sometimes, TRH not only stimulates the release of TSH, but also promotes the release of prolactin. In non-pregnant women, an excess amount of prolactin can lead to anovulatory cycles (no ovulation) and even to amenorrhea (absence of menstruation).

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Moreover, thyroid hormones regulate the bioavailability of sex hormones by modulating the concentrations of HNF4alpha. This factor, coming from the liver, affects the concentrations of binding proteins of sex hormones (SHBG). Conversely, sex hormones influence the bioavailability of thyroid hormones. With estrogen therapy, for instance, the concentrations of TBG increases, which raises the need for thyroid medication in women with hypothyroidism.