Which factor is known to decrease sex hormone binding globulin?

Obesity is known to decrease sex hormone-binding globulin (SHBG) levels. SHBG is a glycoprotein produced by the liver that binds to sex hormones, primarily testosterone and estradiol, regulating their availability in the bloodstream. In individuals with obesity, increased insulin resistance and elevated insulin levels can lead to a reduction in SHBG production. The higher amounts of free sex hormones due to lower SHBG levels can contribute to various metabolic and reproductive issues associated with obesity, such as polycystic ovary syndrome (PCOS) in women.

While hypoglycemia, chronic stress, and vitamin D deficiency may affect hormonal regulation and metabolic processes in the body, they do not have the same direct relationship with SHBG levels as obesity does. Hence, obesity is the most significant and well-researched factor that leads to decreased SHBG levels.