A: You may notice that your lab tests list two values for testosterone— total testosterone and free testosterone. That is because testosterone can be bound to other proteins in the bloodstream—most notable sex hormone binding globulin (SHBG)—or can be unbound (free).

Only free testosterone can be used by the body and therefore free testosterone is the more important result to consider. It is possible (in fact quite common) to have a normal total testosterone level, but low free testosterone. This is primarily affected by the amount of SHBG circulating in the bloodstream. Therefore, as SHBG levels rise, free testosterone decreases. Conversely, by decreasing SHBG levels, a man can increase his bioavailable testosterone.

 

A: Among other things, SHBG rises with malnutrition, alcohol abuse, smoking, cirrhosis, and low growth hormone levels.

 

A: Not surprisingly, diet and exercise help. Specifically, high-protein diets can reduce SHBG levels. Whey protein is an easily absorbed supplemental protein source. As far as supplements go, boron, zinc, vitamin D, calcium, magnesium, and fish oil have been shown to reduce SHBG. Additionally, an herb native to Asia called tongkat ali has been shown to decrease circulating SHBG levels and is commonly used to stabilize free testosterone.