Sex hormone-binding globulin (SHBG) is thought to mainly function as a transporter and reservoir for the estradiol and testosterone sex hormones. However it has also been demonstrated that SHBG can bind to a cell surface receptor (SHBG-R). The SHBG-R has not been completely characterized. A subset of steroids are able to bind to the SHBG/SHBG-R complex resulting in an activation of adenylyl cyclase and synthesis of the cAMP second messenger.  Hence the SHBG/SHBG-R complex appears to act as a transmembrane steroid receptor that is capable of transmitting signals to the interior of cells.
Some, semi-common conditions that affect a good portion of society, and more who are non optimal excercisers: methylation problems (active folate, B12, b6 issues pyrroles (zinc, active b6, gla and some magnesium) (see Walsh protocols for a wide range of conditions from variouse malfunction, including sulphication issues, includes methylation) these are issues common in autism spectrum disorders, with Asperger’s being part of the disorder, I suspect trials on University students that be skewed by this), nor-adrenalin, copper vitamin C, iron or zinc and other issues, and people with ATP dysfunction, such as from the virus associated with chronic fatigue. Either a supplement addresses issues, or the underlying physiology might have to run smoothly to maximise it’s affect.