Does vitamin D influence testosterone levels and reproductive endocrine function?

Vitamin D plays an active role in steroidogenesis and reproductive endocrine health, though its effects on sex hormones are highly population- and sex-specific.

Clinical and hormonal associations

• Sex-specific differences: While observational data in some male cohorts show a positive correlation between vitamin D and total testosterone, this association is highly confounded by body mass index (BMI). Conversely, in healthy adult female populations, vitamin D deficiency is associated with a more androgenic profile, characterized by higher free testosterone and lower sex hormone-binding globulin (SHBG).
• Pathological states: In women with polycystic ovary syndrome (PCOS), vitamin D deficiency correlates with heightened androgen excess. Clinical trials demonstrate that therapeutic supplementation in these cohorts helps restore hormonal balance by raising SHBG and decreasing both total testosterone and the free androgen index (FAI).

Mechanistic endocrine pathways

• Receptor localization: The vitamin D receptor (VDR) is widely expressed in reproductive tissues—including ovarian granulosa, theca, and luteal cells, as well as endometrial and placental tissues—enabling localized, genomic active vitamin D (calcitriol) signaling.
• Enzymatic regulation: Vitamin D signaling directly modulates the transcription of key steroidogenic enzymes, specifically regulating CYP19A1 (aromatase) to facilitate the conversion of androgens into estrogens. It also interacts with CYP11A1, which catalyzes the rate-limiting step of steroidogenesis.
• Functional outcomes: In knock-out models, VDR-null status leads to severe gonadal insufficiency and impaired folliculogenesis, highlighting the essential role of this pathway in maintaining healthy female reproductive physiology and local ovarian tissue function.

Bottom line

• While vitamin D deficiency is linked to lower testosterone in men, it correlates with elevated free androgens in healthy women; thus, maintaining optimal vitamin D status is critical for female endocrine health by regulating key steroidogenic enzymes like CYP19A1 and sustaining balanced hormone synthesis.