The Journal of urology2026n = 2,205 men
Cross SectionalHuman
This study looked at whether time spent outdoors is linked to testosterone in men. It analyzed 2,205 men in the US National Health and Nutrition Examination Survey, tracking daily outdoor…
Nutrients2026n = 75 enrolled, 70 completed
RCTHuman
This study looked at whether vitamin D changes how well metformin (a common diabetes drug that lowers blood sugar) can bring down prolactin (a pituitary hormone that suppresses testosterone when…
European urology focus2026n = 2209
Cross SectionalHuman
This study set out to see whether exposure to bright light is linked to testosterone in men, an area far less studied than diet and exercise. It analyzed data from…
Nutrients2026n = 21 comparison-level records from 18 reports
Meta AnalysisHuman
This systematic review and meta-analysis set out to see whether vitamin D supplements raise testosterone or related markers in men. It pooled randomized trials measuring total testosterone, SHBG (sex hormone-binding…
Journal of medical biochemistry2025n = 64 couples
Cross SectionalHuman
This study set out to identify which factors might influence pregnancy success in couples undergoing assisted reproductive technology (ART, fertility treatments that handle eggs and sperm outside the body). It…
The journal of nutrition, health & aging2025n = 1,292 (53% women)
CohortHuman
This study looked at whether vitamin D levels in the blood are linked to developing sarcopenia (age-related muscle loss) in older adults. It followed 1,292 Korean adults aged 70-84 without…
The Journal of clinical endocrinology and metabolism2017n = 98
RCTHuman
This study set out to test whether vitamin D supplements raise testosterone in healthy men. It randomly assigned 98 men with normal testosterone but low vitamin D to a high…
Andrology2014n = 225
Cross SectionalHuman
This study looked at whether vitamin D levels track with testosterone, and with hypogonadism (when the testicles do not make enough testosterone, which shows up as low drive, fatigue and…