So I found an article related to long-term boron use and it suggests it can increase Estradiol. This article may be bro science though. On top of that, it mentions that boron may reduce SHBG creating a higher Free T count...? As I have discovered over my time using the "interwebs" there's seldom consensus

Ultimately, I am not concerned about E going up because I'm looking for the joint benefits, longer telomeres and a younger age profile. Ah, the fountain of youth!
"Estrogen Reduction: Boron increases testosterone, but it can reduce estrogen levels as well. The same study mentioned above found that over the course of a week, 10mg of boron consumption decreased serum estradiol levels a whopping 39%! However, this effect may not be sustainable, as another study revealed that longer term supplementation, 4 weeks, actually led to increases in serum estradiol levels. So it may be best to keep supplementation limited to short periods of time. I suggest you cycle Boron 2 weeks on, 1 week off to reap all the benefits without the negatives."
When it comes to nutrients we consider for peak performance, Boron is far from being one of the more popular ones. In fact, chances are you’ve never even heard of it. Regardless, you’re in the right place. When it comes to nutrients we consider for peak performance, Boron is far from being one...
breakingmuscle.com