Effect Of Vitamin D Supplementation On Testosterone Levels In Men, Hormone and Metabolic Research, March 2011

From abstract:

The male reproductive tract has been identified as a target tissue for vitamin D, and previous data suggest an association of 25-hydroxyvitamin D [25(OH)D] with testosterone levels in men.

Participants received either 83 μg (3,332 IU) vitamin D daily for 1 year (n = 31) or placebo (n = 23).

Mean circulating 25(OH)D concentrations increased significantly by 53.5 nmol/l in the vitamin D group, but remained almost constant in the placebo group.

Compared to baseline values, a significant increase in total testosterone levels, bioactive testosterone, and free testosterone levels were observed in the vitamin D supplemented group [all measures p = 0.001]. By contrast, there was no significant change in any testosterone measure in the placebo group.

Might that extra vitamin D and testosterone improve muscle strength? It doesn’t appear so:

Vitamin D Supplementation Does Not Enhance Resistance Training-Induced Gains In Muscle Strength And Lean Body Mass In Vitamin D Deficient Young Men, European Journal of Applied Physiology, July 2021

In fact:

” … whereas strength gains in chest press and seated row were greater (P < 0.05) in placebo group compared to vitamin D group.”

From Harvard Medical School:

Problems associated with abnormally high testosterone levels in men include:

Low sperm counts, shrinking of the testicles and impotence
Heart muscle damage and increased risk of heart attack
Prostate enlargement with difficulty urinating
Liver disease
Acne
Fluid retention with swelling of the legs and feet
Weight gain, perhaps related in part to increased appetite
High blood pressure and cholesterol
Insomnia
Headaches
Increased muscle mass
Increased risk of blood clots
Stunted growth in adolescents
Uncharacteristically aggressive behavior
Mood swings, euphoria, irritability, impaired judgment, delusions

So, men who take vitamin D will increase their testosterone levels which may make it difficult to sleep and pee, increase risks for prostate cancer and heart attack, and put them in a bad mood. Is that what this says? Vitamin D? So many men are taking vitamin D…