Short answer: The trials so far mostly say no. A 2011 study of 54 overweight men low in vitamin D saw total testosterone rise over a year on vitamin D, but that was a change within the group. Two later placebo-controlled trials from the same Austrian team, one in about 100 men with normal testosterone and one in about 100 men with low testosterone, found no effect on total testosterone after 12 weeks.
Studies that look at large groups of men have found that men with lower vitamin D levels tend to have lower testosterone, and the 2011 trial authors note that the male reproductive tract is a target tissue for vitamin D. That link led to the idea that a vitamin D supplement might raise testosterone. A link in observational data does not show cause, so the question has to be tested in trials where men are randomly given vitamin D or a placebo.
| Study | Men | Vitamin D given | Result |
|---|---|---|---|
| Pilz 2011 | 54 overweight men in a weight-loss program, low vitamin D at the start (31 on vitamin D, 23 on placebo) | 3,332 IU a day for 1 year | Total testosterone rose from 10.7 to 13.4 nmol/L in the vitamin D group; no significant change on placebo |
| Lerchbaum 2017 | 98 healthy men with normal testosterone and vitamin D below 75 nmol/L | 20,000 IU a week for 12 weeks | No significant effect on total testosterone, measured by mass spectrometry |
| Lerchbaum 2019 | 94 healthy men with total testosterone below 10.4 nmol/L | 20,000 IU a week for 12 weeks | No significant effect on total testosterone or the other hormones measured |
The 2011 result compared each group with its own starting values rather than reporting a head-to-head difference between vitamin D and placebo, and the men were also in a weight-loss program at the same time. The authors called for more trials. The two later trials were built to answer that, used a placebo, and found nothing. The 2017 trial also saw a small drop in one measure of insulin sensitivity on vitamin D.
All three trials were small and run in Austria or Germany. None tested men already on testosterone therapy, whose testosterone level comes mainly from the dose, and none reported on symptoms.
Vitamin D is still a nutrient people need for bone and muscle. The NIH Office of Dietary Supplements lists an upper limit of 4,000 IU a day for adults; the trials above used amounts below that, averaged per day, under supervision. See the vitamin D3 page for levels and limits.
If a testosterone result is low, the cause, the repeat test and the treatment are for the prescriber. A vitamin D blood test (25-hydroxyvitamin D) can be ordered alongside if there is a reason to check it. Dose Track can log a daily vitamin D next to testosterone doses and lab dates, so a later result can be read against what was being taken at the time.
Read more on Dose Track: Vitamin D3 · Low testosterone · Free testosterone · Randomized controlled trial