The fact that they're necessary conditions for its production doesn't mean they're sufficient, though. It doesn't follow that you can just take a vitamin pill and get some sunlight and you'll naturally have high levels of testosterone.
The evidence is strongly suggestive that vitamin D supplementation has an effect on testosterone levels in men.
On a purely anecdotal, personal level, I had my free test checked some years back, before I started vitamin D supplementation. After supplementing with 10,000 IUs a day for around a year, I had it checked again and it was significantly higher (I don't have the numbers now, sorry).
10 000 IU a day?
Was that a typo? How did you got that target?
Just asking because I was considering 10 000 IU a week following my MDs advice (which is already higher than what it the normal off the shelf dose: 1000 IU a day).
Although safe, according to current search, there's no benefits from supplementing 10,000 UI daily (2,000-5,000 being recommended dose) — http://examine.com/supplements/Vitamin+D/
This doesn't prove that 10,000 is unnecessary, but there's no proof that it's necessary either :) (or is there?)
If you're deficient you'll have lower test levels. That doesn't mean you can megadose vitamin D to get high test levels, just that if you don't have adequate supply you'll have lower than normal levels.
Specifics? Evidence?