Testosterone Action versus Testosterone Levels: Why SHBG Matters

By Neel Duggal, January 10, 2023

Testosterone and SHBGSex Hormone Binding Globulin or SHBG is essential for maximizing the availability of testosterone, the biomarker every man wants to measure. Today, science is telling us that both men and women need an optimized hormonal profile, and testosterone is widely known to be important for men.

But growing research points out the importance of testosterone for women. Blood testing is a practical way to "look under the hood" and get guidance to optimizing oneself. In this blog we will discover how SHBG is like a key and unlocks the door to optimizing health and performance.

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Why SHBG is important for your health and performance

Sex hormone binding globulin (SHBG) is a glycoprotein primarily produced in the liver and most commonly found in the bloodstream. It binds to any of 17 sex hormones, including testosterone and estrogen, and transports these chemicals throughout the body. Testosterone and sex hormones are referred to as “bound” when attached to SHBG. When these hormones are not bound to SHBG, they are referred to as “free”, or “bioavailable”, and can freely exert their effects upon your body. The sum of bound and free testosterone is referred to as total testosterone.

It is well-known that a proper balance of testosterone and other sex hormones have a crucial impact on your health. Recent research has unveiled that imbalances of sex hormones are often preceded by abnormalities in SHBG. High levels of sex hormones can lead to excess growth of cells leading to the formation of certain cancers such as breast cancer [1]. Low SHBG is also associated with elevated levels of triglycerides and low-density lipoprotein (LDL) [2]. Because of this, low levels of SHBG are linked with multiple cardiovascular illnesses in both sexes, including heart disease, type 2 diabetes, and high blood pressure [3].

Excessively high SHBG is problematic especially for males and athletes because it decreases the amount of free testosterone. High levels of SHBG are associated with infertility, a decreased sex drive, and erectile dysfunction, especially when total testosterone levels are already low [4]. In both men and women, low levels of free testosterone can result in reduced muscle growth and impaired post-workout recovery [5]. Additionally, recent research suggests that high levels of SHBG bind to estrogen and reduce bone mass in both men and women- potentially leading to osteoporosis. Thus, optimal SHBG levels are crucial in maintaining proper bone health and some experts are now suggesting routine measurement of SHBG as a useful new marker for predicting severe bone diseases [6].

So how do you know if you need to increase or decrease your SHBG levels? The only way is to get your blood tested using InsideTracker. Once you know your SHBG levels, you can make the proper lifestyle changes to modify your levels and optimize your health. Below we examine some research showing how two diets (calorie-restricted and vegetarian) and a rigorous physical exercise regimen impact your levels of SHBG and testosterone.


SHBG levels on a chart

Counting calories: Increasing your SHBG & reducing your testosterone

A sustained, reduced calorie diet may significantly increase SHBG levels in women. In a single-blind, randomized control study, researchers assessed the long-term impacts of a diet reduced by 10% in calories over 12 months in two groups: 117 females consuming a reduced-calorie diet with no exercise regimen and 118 consuming a reduced-calorie diet in conjunction with a moderately intense aerobic exercise regimen.  A group of 87 females participating in neither the exercise regimen nor the reduced-calorie intervention served as the experimental controls. After the 12 month study, researchers observed that serum SHBG increased by 22.4% in the diet intervention group and 25.8% in the diet and exercise intervention group in comparison with the control group [7]. Similarly, free estrogen decreased by 21.4% and 25.8% respectively for the diet intervention group and diet & exercise intervention group [7]. Additionally, free testosterone decreased by 10.0% and 15.6% respectively in the reduced-calorie diet only group and the reduced-calorie diet & exercise intervention group [7]. Collectively, these findings suggest that a reduced calorie diet- especially in conjunction with aerobic exercise- is an effective method in significantly increasing SHBG levels and decreasing levels of free sex hormones such as testosterone and estradiol.

Key Takeaways: A calorie-restricted diet is a useful weight-loss method if you are seeking to increase SHBG levels and decrease levels of certain serum sex hormones such as testosterone and estrogen. However, if you are looking to increase free testosterone and estradiol for performance or health related reasons, a calorie-restricted diet is a poor weight-loss choice and may harm your health.

Health effects of underfueling

Does overtraining lead to overactive SHBG?

In a 2011 Finnish study, researchers assessed the impacts of overtraining on levels of SHBG and total testosterone (TT). They enlisted 57 males with an average of age of 20 years and tested them during 8 weeks of basic military training in cold, winter temperatures (-13.6 Celsius average). The physical regimen started at 2 hours/day in week one and increased to 7 hours/day by week 8. According to the researchers, these subjects had their first experience of very demanding physical training, eating outdoors, and performing overnight exercises in a forest. As a result, they surmised that these men experienced overtraining and would experience physiological effects such as a sudden decrease in performance. The researchers took blood samples of the subjects after 12 hours of fasting before weeks 1, 4, and 7 where the first blood sample served as the baseline blood levels of SHBG and TT. Researchers revealed that TT remained the same as baseline after the 4th and 7th weeks. While serum SHBG concentrations remained the same after week 4, they increased after week 7 [8]. Because of the increase in SHBG and same level of TT, the free serum testosterone levels decreased resulting in lower muscle recovery and ultimately poorer physical performance.

Key Takeaways: Overtraining leads to increases in SHBG which reduces free testosterone and facilitates processes that can lead to reduced physical recovery. Thus, it is crucial for people participating in physically demanding activities (i.e. athletes, military personnel) and those at risk for diseases associated with high SHBG such as osteoporosis to carefully monitor their biomarkers to prevent overtraining.


Vegetarianism and SHBG

In a 2009 research study, scientists assessed the impact of a vegetarian-based protein diet on serum levels of SHBG in middle-aged women. They recruited 21 middle-aged female omnivores and 19 middle-aged female vegetarians and observed them in a cross-sectional study over one year. The diets of the 19 vegetarians included vegans (consuming no animal products), lacto-vegetarians (consuming dairy products), and lacto-ovo-vegetarians (consuming eggs and dairy products). Subjects in both groups exercised for 0-3 hours a week and consumed similar quantities of protein per kilogram of body weight- though the vegetarians consumed more plant-based protein and the omnivores more animal-based protein.  Every three months, the researchers assessed the levels of serum sex hormones and SHBG in their blood. At the conclusion of the study, researchers observed similar levels of total testosterone in vegetarians and omnivores (respectively 1.79 nmol/L vs. 1.76 nmol/L) [9]. In contrast, the vegetarians had a 50% higher level of SHBG than did the omnivores (46 vs. 69 nmol/l) [9]. This suggests that a vegetarian-based protein diet increases SHBG without affecting total testosterone and ultimately leading to a decreasee in free testosterone.

Key Takeaways: A diet high in vegetable-based protein increases SHBG without decreasing total testosterone. However, women concerned with having low levels of free sex hormones should consider consuming more animal-based proteins.



Using SHBG to optimize your health                          

Sex Hormone-Binding Globulin is an overlooked biomarker that has a critical impact on your health and athletic performance. Do you need to start consuming a vegetarian diet to increase your SHBG and lower your risk of cardiovascular diseases? Or do you need to increase your calorie intake to unchain testosterone and fuel muscle growth after your exhausting exercise regimen? The only way to know is to discover your SHBG levels today and modify your lifestyle to take control of your health.

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List of References

[1] Allen NE, Key TJ, Dossus L, et al. Endogenous sex hormones and endometrial cancer risk in women in the European Prospective Investigation into Cancer and Nutrition (EPIC). Endocr Relat Cancer. 2008 Jun;15(2):485-97.

[2] Sarkar NN. Hormonal profiles behind the heart of a man. Cardiol J. 2009;16(4):300-6.

[3] Calderon-Margalit R, Schwartz SM, Wellons MF, et al. Prospective association of serum androgens and sex hormone-binding globulin with subclinical cardiovascular disease in young adult women: the “Coronary Artery Risk Development in Young Adults” women’s study. J Clin Endocrinol Metab. 2010 Sep;95(9):4424-31.

[4] Ahn, H. S., C. M. Park, and S. W. Lee. "The clinical relevance of sex hormone levels and sexual activity in the ageing male." BJU international 89.6 (2002): 526-530.

[5] Griggs, ROBERT C., et al. "Effect of testosterone on muscle mass and muscle protein synthesis." Journal of Applied Physiology 66.1 (1989): 498-503.

[6] Hoppé, Emmanuel, et al. "Sex hormone-binding globulin in osteoporosis." Joint Bone Spine 77.4 (2010): 306-312.

[7] Campbell, Kristin L., et al. "Reduced-calorie dietary weight loss, exercise, and sex hormones in postmenopausal women: randomized controlled trial." Journal of Clinical Oncology (2012): JCO-2011.

[8] Tanskanen, Minna M., et al. "Serum Sex Hormone–Binding Globulin and Cortisol Concentrations are Associated With Overreaching During Strenuous Military Training." The Journal of Strength & Conditioning Research 25.3 (2011): 787-797.

[9] Aubertin-Leheudre, Mylene, and Herman Adlercreutz. "Relationship between animal protein intake and muscle mass index in healthy women." British journal of nutrition 102.12 (2009): 1803-1810.

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