What is SHBG?
Sex Hormone Binding Globulin (SHBG) is synthesized in the liver, and in the blood it transports and regulates the access of sex steroids to their target tissues. Variants in this gene have been shown to lead to lower testosterone, calculated free testosterone, and SHBG in men.
The SHBG Genes and Testosterone
The associations of rs12150660 and rs6258 were confirmed in the three replication cohorts showing that men with the GT and TT genotype for rs12150660 had higher levels of testosterone, free testosterone, and SHBG, while the TC genotype for rs6258 had lower testosterone, calculated free testosterone and SHBG compared to the wild-type CC genotype. Not enough subjects had the homozygous TT genotype to produce data.
The rs6258 was found to substantially affect SHBG binding affinity by lowering free testosterone levels. The lowest testosterone levels were found in those with the GG genotype of rs1210660 and the TC or TT genotype of rs6258. You can check your rs1210660 genotype in the Hormones section.
Optimal Testosterone and Men’s Health
Only a small fraction of the total testosterone – from 1% to 2% – is free in the blood and biologically active. About 40% to 70% of total testosterone travels around with SHBG and is not available to your cells. This means a large part of total testosterone may not be biologically active and available to your cells if SHBG is high even though your testosterone is in a healthy range.
On the other hand, low SHBG and lower total testosterone may be misleading since more of that testosterone is free and active. However, a study of men in the U.S indicated that men with lower concentrations of total testosterone and SHBG had a higher likelihood of having metabolic syndrome than those with higher concentrations.
Symptoms are one of the best indicators of understanding how much free testosterone is getting delivered to the target tissues. Low testosterone in men will affect sex drive, mood, muscle mass, confidence, ambition, and cardiovascular health. Men whose testosterone levels were slightly above average were 45% less likely to have high blood pressure, 72% less likely to have experienced a heart attack, and 75% less likely to be obese than men whose levels were slightly below average. Optimal testosterone is between 550-990ng/ml according to the Journal of the American College of Cardiology.
A study published in the International Journal of Sports Medicine revealed that strength athletes who consumed the most fat also had the highest testosterone levels, however, excessive protein also compromised the anabolic response. A study from the Journal of Clinical Endocrinology & Metabolism reported that a low-fat, high-fiber diet reduced testosterone levels in middle-aged men.
Research has also found that that magnesium, zinc, vitamin D, fish or fish oil, boron, compound weight lifting, sprints, chopping wood, and eight hours of sleep per night all positively influence SHBG and testosterone levels.