I believe most supplements / vitamins have a threshold, where really low levels causes obvious health problems, while being somewhat deficient isn't obvious but supplementing will improve or change some blood levels like E2 for FT, as an example.
But once you cross that threshold of no longer even being somewhat deficient, more isn't going to produce more of the same result. And more can often start producing a negative result by either competing with other supplements / vitamins or shutting down / creating a negative feedback loop.
An easy example is iodine, where you need iodine for many process, the thyroid especially. However, if you take a lot of iodine (too much) it will cause your TSH to start to rise and T3 fall.
When I first took boron, I wasn't on TRT and it did raise FT / ET, though not enough to be able to avoid TRT.
It didn't have any noticeable effect on SHBG, I have read boron is known to play a role in extending the half-life of vitamin D and estrogen and boosts magnesium absorption, which maybe the the reason FT/E2 went up. However measuring SHBG after starting TRT shows a steady rise in SHBG regardless of my continuing to take boron.
I would take 3-6 mg boron and not worry about SHBG being affected, though I can't say boron has had any negative or positive effects after the intial change a couple of years ago.
