Not yet investigated
What we have so far
It decides how much of your testosterone is available, so a normal total with a high SHBG is a low free level — and insulin drives SHBG down.
This star is on the map because the show intends to take the question apart properly — the trials, how it is actually tested, whether the thing sold is the thing studied. That work is not done yet, and nothing here should be read as a conclusion. When the investigation is published it will appear on this page.