Male fertility and thyroid hormones

Area of Science:

• Endocrinology
• Reproductive Medicine
• Andrology

Background:

• In vitro studies suggest testicular unresponsiveness to thyroid hormones.
• In vivo investigation is needed to clarify the relationship between thyroid hormones and male reproductive function.

Purpose of the Study:

• To evaluate the correlation between blood concentrations of thyroid hormones and male reproductive parameters.
• To determine if thyroid hormones influence sperm count and motility in vivo.

Main Methods:

• Measured total blood concentrations of thyroxine (T4) and free thyroxine index (IT4L) in normal and infertile subjects.
• Assessed sperm count and percentage of motile spermatozoa.
• Analyzed correlations between hormone levels and reproductive parameters.

Main Results:

• T4 concentrations showed a significant positive correlation with sperm count (r = 0.43, p < 0.02).
• T4 concentrations also correlated positively with the percentage of motile spermatozoa (r = 0.48, p < 0.01).
• No significant correlation was found for triiodothyronine (T3) or free thyroxine index (IT4L).

Conclusions:

• Thyroid gland function is linked to the hypothalamo-hypophyseotesticular axis in men.
• Peripheral metabolism of circulating thyroid hormones does not appear to be involved in this relationship.
• Thyroxine (T4) levels are associated with male reproductive capacity.