Free Testosterone Levels | The Ultimate Guide

Dr. Mike Jansen

Last Updated April 9, 2022

Dr. Mike Jansen

 April 9, 2022

What are healthy free testosterone levels?

Inside this detailed guide, we’ll breakdown everything you MUST know about free testosterone levels in men, including:

  • Free testosterone levels by age
  • Total-T vs. Free T
  • Why Free-T matters

…and so much more!…

Testosterone is one of the most important hormones in the human body. Testosterone plays a huge role for athletes who are trying to build muscle mass and strength. However, it’s also extremely important for your overall health.

If you do not produce enough testosterone then you may be at increased risk for cardiovascular disease, type 2 diabetes, metabolic syndrome, depression, and many other illnesses. Understanding the importance of healthy free testosterone levels may be one of the most important things you can do for your overall health.

Disclaimer: The contents of are for informational and educational purposes. We do not provide legal advice. Likewise, we do not provide medical advice, diagnosis, or treatment. Please consult your physician prior to consuming any over-the-counter supplements, like a natural testosterone booster, and/or getting a prescription for a pharmaceutical medication. Your access to is subject to our full disclaimer and terms of use.

What is Testosterone?

Testosterone is one of the most important hormones in the human body. Testosterone is the male sex hormone and is responsible for many of the physical characteristics that you see in men including facial hair and broad shoulders.

Testosterone is primarily produced in the testes in men, although women also produce some testosterone in their ovaries. Research has shown that normal testosterone levels are essential for optimal health. Men with low testosterone levels often suffer from low energy, sexual dysfunction, depression, and cardiovascular disease.

Men who are able to raise their testosterone levels through medical interventions including testosterone replacement therapy often see a rapid improvement in their overall health and well-being [13].

Unfortunately, testosterone levels are declining in most countries, especially in older and younger men [45]. Research shows that men’s testosterone levels have been declining about 1% per year every year sense 1950, and this trend shows no signs of slowing down.

There are many reasons for this: testicular failure, pituitary axis abnormalities and environmental toxins are three of the most common reasons identified by researchers [67]. Other reasons may include obesity, malnutrition, improper exercise, poor sleeping habits and increasing levels of stress.

Understanding testosterone (and especially free testosterone) is extremely important for anyone interested in optimizing their health, energy levels, sexual performance, or athletic abilities.

Free Testosterone Levels

What is Free Testosterone?

There are two ways of measuring testosterone levels: total testosterone and free testosterone.

Total testosterone is a measure of the total amount of testosterone that is floating around in your blood at a time. Free testosterone is a little different: it measures the amount of testosterone in your blood that can bind to the cells in your body and exert its physiological effects. In other words, free testosterone measures the amount of “active” testosterone in your bloodstream.

Free testosterone plays a huge role in men’s and women’s health. Research shows that advanced age, a poor diet, diabetes and hypertension are all associated with low free testosterone levels [89]. In fact, low free testosterone levels are associated with mobility restrictions, frailty, osteoporosis and reduced athletic performance [1011]. Many unwanted health conditions including cardiovascular disease, cancer and prostate disease are also caused by low free testosterone levels [1014].

Research has identified many benefits to having higher free testosterone levels. Some of the most obvious benefits include increased muscle mass, improved athletic performance and improved sexual function and fertility [1518]. Some of the less obvious benefits of free testosterone include improved cardiovascular health, decreased symptoms of depression and improved cognitive function [1924].

In fact, it’s hard to think of a bodily system that is not positively impacted by optimal free testosterone levels. This is one of the reasons medical treatments designed to raise your free testosterone levels including testosterone replacement therapy are becoming so popular in recent years.

Free Testosterone Levels in Men | Ultimate Guide

There are two main ways to measure your testosterone levels: total testosterone and free testosterone. Most people focus only on their total testosterone levels. Unfortunately, this is a mistake, as your free testosterone levels are probably even more important than your total testosterone levels. Let me explain.

Total testosterone measures all of the testosterone that is floating around in your bloodstream at any one time. The problem with the total testosterone measurement is about 98% of the testosterone in your bloodstream is bound to one of two proteins: sex hormone binding globulin (shgb) or albumin.

When your testosterone binds to one of these hormones, it becomes inactive. The other 2% of your testosterone that is not bound to one of these two hormones is called your “free testosterone” because it is free to bind to the cells in your body and exert its physiological effects.

Free testosterone is probably a better measurement of your testosterone levels because it only measures the “active” testosterone in your bloodstream. Some individuals can have high total testosterone but lower free testosterone. This shows how important it is to look at your free testosterone levels in addition to your total testosterone levels.

So what are normal free testosterone levels? Normal free testosterone levels in healthy, adult men range from 5.25 – 20.7 ng / dL, or nanograms per deciliter of blood [2531]. This is significantly lower from total testosterone, which ranges from 300 – 1200 ng / dL.

Here is what normal free testosterone levels look like for men of different ages [3239]:

  • Teenage males: 5.25 – 20.7 ng / dL
  • Men in their 20s: 5.25 – 20.7 ng / dL
  • Men in their 30s: 4.65 – 19.0 ng / dL
  • Men in their 40s: 4.26 – 17.1 ng / dL
  • Men in their 50s: 3.87 – 15.6 ng / dL
  • Men in their 60s: 3.47 – 13.9 ng / dL
  • Men in their 70s: 3.08 – 12.2 ng / dL

Free testosterone levels vary enormously from one individual to the next. Free testosterone levels tend to slowly decline as an individual gets older. This is a normal part of aging, but it is also associated with several negative health outcomes.

Free testosterone levels also vary significantly between individuals of the same age group. For example, two men in their 20s can have free testosterone levels of 20.7 and 5.25 ng / dL.

Both men are in the “normal” range for free testosterone levels. However, the second individual is much more likely to experience symptoms of low energy, depression, sexual dysfunction and a host of other signs and symptoms of low testosterone.

Many medical professionals consider the lower end of the free testosterone range as a sign of hypogonadism, or low testosterone levels. The good news is there are many strategies that you can use to raise your free testosterone if you are on the lower end of normal.

These interventions range from natural strategies to medical solutions like testosterone replacement therapy. These options will be covered later in this article.

Signs of Low Free Testosterone in Men

Men (and women) need require a normal amount of free testosterone for optimal health. Most people begin to experience negative signs and symptoms when their testosterone falls below the normal, healthy range. This is why it is so important to identify and treat hypogonadism, or low testosterone levels.

Some signs of low free testosterone such as reduced energy levels can be relatively mild. Others such as increased risk of cardiovascular disease are more serious.

Here are some of the top signs of low-T in men:

  • Reduced muscle mass [4041]
  • Male infertility and reduced sexual performance [4243]
  • Impaired cardiovascular health [1718]
  • Increased risk of depression [4445]
  • Obesity, diabetes and metabolic dysregulation [4445]
  • Reduced cognitive function [2122, 46]

One of the most common signs of low free testosterone levels in men is reduced muscle mass. Testosterone is one of the most important hormones for building muscle mass and strength. Athletes sometimes take supra-physiological doses of testosterone to speed up the muscle-building process.

Most individuals find that their overall muscle mass decreases as their free testosterone levels go down. Low free testosterone levels are one of the main causes of sarcopenia, a muscle-wasting disease. Another common sign of low free testosterone levels is impaired sexual function.

It is well established that low free testosterone levels make it more difficult to achieve or maintain an erection, as well as to conceive during sex [4243]. If your performance in the bedroom is not what it used to be then a decline in your free testosterone levels may be to blame.

Some of the lesser known symptoms of low free testosterone levels include depression and general cognitive decline [2122, 4446]. Finally, many life-threatening conditions including cardiovascular disease, type 2 diabetes and metabolic dysregulation are actually signs of low free testosterone levels, especially in men [1718, 4445].

How to Increase Free Testosterone Levels Naturally

Testosterone plays a critical role in everything from athletic performance to cardiovascular health to sexual performance. If you are suffering from hypogonadism, or low testosterone levels, then increasing your testosterone levels is one of the best things that you can do for your overall health and well-being.

The truth is there are many strategies that you can use right now to raise your testosterone levels. Here are a few of the most effective strategies:

  • Losing weight
  • Resistance training
  • Sexual activity
  • Sleep
  • Vitamin D
  • Ecdysterone

One of the fastest and simplest ways to raise your testosterone levels is to lose weight. Research shows that men who lose weight see a rapid improvement in their total and free testosterone levels. In fact, one study found that the incidence of hypogonadism went down by over 50% in a population that underwent a weight loss program [47]!

Weight loss is especially effective for raising your free testosterone levels because it reduces the size of your fat cells. Inside your fat cells is an enzyme called aromatase. This enzyme has one job: to take the hormone testosterone and convert it into the hormone estrogen.

The bottom line is the more body fat you have, the more your body will convert your testosterone into estrogen and the lower your free testosterone levels will be. Another simple strategy for raising testosterone is to start a resistance training program.

Research shows that lifting weights and engaging in other forms of resistance training such as gymnastics, rock climbing or mixed martial arts has a positive effect on testosterone levels [48]. Another great way to naturally boost your testosterone levels is to engage in sexual activity.

There is plenty of evidence showing men’s testosterone levels increase following sexual activity [49]. This is true both in the short term, or immediately following sexual activity, and for several days after the event. If you are looking for more conservative ways to naturally increase your testosterone levels then improving your sleep habits or getting some extra sunlight are great options.

Research shows that getting at least 7 hours of sleep per night and optimizing your vitamin D levels are two powerful ways to raise your testosterone levels [5051]. Finally, there are some natural testosterone boosting supplements that you can use to raise your T-levels.

One of the most popular products available today is called ecdysterone. This natural substance has been shown in studies to dramatically increase strength and muscle mass in resistance training subjects [5253]. If you are looking for that extra “edge” in the gym, then ecdysterone may be just what you are looking for.

Free Testosterone Levels

How to Increase Free Testosterone Levels with TRT

Testosterone replacement therapy is a medical intervention designed to raise a patient’s total testosterone to the higher end of the normal range.

Testosterone replacement therapy, or TRT, is normally performed under the direct supervision of a doctor. It is completely different from something like steroids, where the goal is to raise one’s total testosterone to unsafe levels.

Here’s how it works: first, the patient discusses their signs and symptoms with their doctor to determine if they might be suffering from low testosterone levels. Next the doctor orders a blood test to determine the patient’s exact testosterone levels.

If the patient does have hypogonadism and is experiencing symptoms of low testosterone then the doctor may prescribe a testosterone medication. Usually this is an injectable form of testosterone or a testosterone gel that can be rubbed on the skin.

Testosterone replacement therapy is one of the fastest, most effective and safest ways to treat hypogonadism, or low testosterone levels, in younger and older men. In fact, multiple meta-analyses performed in 2021 showed that TRT is a safe and effective way to raise one’s total testosterone levels and to reduce or eliminate the symptoms of low T [5457].

Research shows that testosterone replacement therapy is effective for increasing muscle mass and strength, improving cognitive function, decreasing symptoms of depression, improving sexual function, and even reducing the risk of chronic diseases like cardiovascular disease and type 2 diabetes.

Remember, TRT is not about increasing your testosterone as high as possible (like some bodybuilders try to do). Instead, it is designed to replace the testosterone that your body used to produce on its own. The goal of TRT is for you to be at the mid-upper end of the normal range for total testosterone so that you can maximize your overall health and well-being.

Some men do not like the idea of using small insulin needles to administer the testosterone. Injectable forms of testosterone are still the gold-standard administration technique. However, more and more men’s health clinics are using testosterone creams and other treatment strategies with their patients [5859].

The bottom line is TRT is a powerful treatment option for men with low testosterone levels. It is a proven treatment strategy that has helped countless men optimize their health in a safe manner.

The BEST Online TRT Clinic

Testosterone replacement therapy is a very popular treatment option for men suffering from hypogonadism, or low testosterone. There have been many recent developments in how patients get started with TRT. One of the most exciting developments has been the growth of online TRT clinics, or telehealth medicine.

Online TRT clinics are a great option for anyone who thinks they are suffering from the signs and symptoms of low testosterone but does not want to go through the hassle of visiting an in-person clinic. This is very understandable. After all, not everyone wants to wait 30-60 minutes in a clinic when they can do everything from the comfort of their own home.

One of the most popular online TRT clinics is called Fountain TRT. This company was founded by Dr. Doron Stember, a board-certified urologist. The thing that makes Fountain TRT unique from other online clinics is their simple 3-step process that they use with all their patients.

The first thing you do is fill out a questionnaire to see if you have some of the symptoms of low testosterone. Your doctor will schedule a time with you to go over these results using zoom and other video calling services.

If your doctor agrees that you may be suffering from low testosterone then the next step is to perform a blood test to measure your hormone levels. Your doctor will schedule a time for you with one of their partnered lab facilities. He or she will also review the results of the blood test with you so that you understand exactly what your needs are.

Finally, if your doctor agrees that you are a good candidate for testosterone replacement therapy then you will be given a prescription for a testosterone cream. The cream will be delivered directly to your home and your doctor will walk you through step-by-step on how to administer it.

Fountain TRT prefers testosterone creams over the traditional testosterone injections because they are easy to administer and work for a wide variety of patients. If you are looking for a great online TRT provider then we strongly recommend Fountain TRT.

Get hormone therapy today with Fountain TRT...

Free Testosterone Levels | Overall

Testosterone is one of the most important hormones in the human body. In fact, maintaining healthy testosterone levels is one of the most important things that you can do for your overall health and well-being.

Testosterone plays a role in everything from building muscle mass and strength to regulating your sexual and reproductive systems to maintaining a healthy cardiovascular system.

There are two main ways to measure your testosterone levels: total testosterone and free testosterone. Most people focus on their total testosterone. However, your free testosterone is probably even more important. Free testosterone measures the amount of active testosterone in your bloodstream that can exert positive physiological effects.

There are many natural ways to increase your free testosterone including exercising, losing body fat, improving your sleeping habits, and getting enough vitamin D. However, if you are suffering from hypogonadism or clinically low levels of testosterone then testosterone replacement therapy may be a viable treatment option.

TRT has been shown to be safe and effective when performed under the supervision of a doctor. If you are looking for an online TRT provider then Fountain TRT is a great choice.


  1. Al-Zoubi RM, Yassin AA, Alwani M, Al-Qudimat A, Aboumarzouk OM, Zarour A, Al Ansari A. A systematic review on the latest developments in testosterone therapy: Innovations, advances, and paradigm shifts. Arab J Urol. 2021 Aug 8;19(3):370-375. doi: 10.1080/2090598X.2021.1959260. PMID: 34552788; PMCID: PMC8451690.
  2. Kim SH, Park JJ, Kim KH, Yang HJ, Kim DS, Lee CH, Jeon YS, Shim SR, Kim JH. Efficacy of testosterone replacement therapy for treating metabolic disturbances in late-onset hypogonadism: a systematic review and meta-analysis. Int Urol Nephrol. 2021 Sep;53(9):1733-1746. doi: 10.1007/s11255-021-02876-w. Epub 2021 Jun 5. PMID: 34089171.
  3. Lunenfeld B, Mskhalaya G, Zitzmann M, Arver S, Kalinchenko S, Tishova Y, Morgentaler A. Recommendations on the diagnosis, treatment and monitoring of hypogonadism in men. Aging Male. 2015 Mar;18(1):5-15. doi: 10.3109/13685538.2015.1004049. Epub 2015 Feb 6. PMID: 25657080; PMCID: PMC4648196.
  4. Millar AC, Lau ANC, Tomlinson G, Kraguljac A, Simel DL, Detsky AS, Lipscombe LL. Predicting low testosterone in aging men: a systematic review. CMAJ. 2016 Sep 20;188(13):E321-E330. doi: 10.1503/cmaj.150262. Epub 2016 Jun 20. PMID: 27325129; PMCID: PMC5026531.
  5. Liu YJ, Shen XB, Yu N, et al. Prevalence of late-onset hypogonadism among middle-aged and elderly males in China: results from a national survey. Asian J Androl. 2021;23(2):170-177. doi:10.4103/aja.aja_59_20
  6. Golan R, Scovell JM, Ramasamy R. Age-related testosterone decline is due to waning of both testicular and hypothalamic-pituitary function. Aging Male. 2015;18(3):201-4. doi: 10.3109/13685538.2015.1052392. Epub 2015 Jun 15. PMID: 26075536; PMCID: PMC4816459.
  7. Swee DS, Gan EH. Late-Onset Hypogonadism as Primary Testicular Failure. Front Endocrinol (Lausanne). 2019 Jun 12;10:372. doi: 10.3389/fendo.2019.00372. PMID: 31244778; PMCID: PMC6581721.
  8. Cardarelli R, Singh M, Meyer J, Balyakina E, Perez O, King M. The Association of Free Testosterone Levels in Men and Lifestyle Factors and Chronic Disease Status: A North Texas Healthy Heart Study. J Prim Care Community Health. 2014 Jul;5(3):173-9. doi: 10.1177/2150131913520234. Epub 2014 Jan 26. PMID: 24468578.
  9. Zhang J, Li X, Cai Z, Li H, Yang B. Association between testosterone with type 2 diabetes in adult males, a meta-analysis and trial sequential analysis. Aging Male. 2020 Dec;23(5):607-618. doi: 10.1080/13685538.2018.1557139. Epub 2019 Jan 16. PMID: 30651030.
  10. Krasnoff JB, Basaria S, Pencina MJ, et al. Free testosterone levels are associated with mobility limitation and physical performance in community-dwelling men: the Framingham Offspring Study. J Clin Endocrinol Metab. 2010;95(6):2790-2799. doi:10.1210/jc.2009-2680
  11. Hyde Z, Flicker L, Almeida OP, Hankey GJ, McCaul KA, Chubb SA, Yeap BB. Low free testosterone predicts frailty in older men: the health in men study. J Clin Endocrinol Metab. 2010 Jul;95(7):3165-72. doi: 10.1210/jc.2009-2754. Epub 2010 Apr 21. PMID: 20410223.
  12. Hyde Z, Norman PE, Flicker L, Hankey GJ, Almeida OP, McCaul KA, Chubb SA, Yeap BB. Low free testosterone predicts mortality from cardiovascular disease but not other causes: the Health in Men Study. J Clin Endocrinol Metab. 2012 Jan;97(1):179-89. doi: 10.1210/jc.2011-1617. Epub 2011 Oct 19. PMID: 22013106.
  13. Watts EL, Appleby PN, Perez-Cornago A, Bueno-de-Mesquita HB, Chan JM, Chen C, Cohn BA, Cook MB, Flicker L, Freedman ND, Giles GG, Giovannucci E, Gislefoss RE, Hankey GJ, Kaaks R, Knekt P, Kolonel LN, Kubo T, Le Marchand L, Luben RN, Luostarinen T, Männistö S, Metter EJ, Mikami K, Milne RL, Ozasa K, Platz EA, Quirós JR, Rissanen H, Sawada N, Stampfer M, Stanczyk FZ, Stattin P, Tamakoshi A, Tangen CM, Thompson IM, Tsilidis KK, Tsugane S, Ursin G, Vatten L, Weiss NS, Yeap BB, Allen NE, Key TJ, Travis RC. Low Free Testosterone and Prostate Cancer Risk: A Collaborative Analysis of 20 Prospective Studies. Eur Urol. 2018 Nov;74(5):585-594. doi: 10.1016/j.eururo.2018.07.024. Epub 2018 Aug 1. PMID: 30077399; PMCID: PMC6195673.
  14. Li, Tian & Sun, Xiangzhou & Chen, Liheng. (2019). Free testosterone value before radical prostatectomy is related to oncologic outcomes and post-operative erectile function. BMC Cancer. 19. 10.1186/s12885-018-5148-1.
  15. Alyssa N Varanoske, Lee M Margolis, Stefan M Pasiakos, Effects of Testosterone on Serum Concentrations, Fat-free Mass, and Physical Performance by Population: A Meta-analysis, Journal of the Endocrine Society, Volume 4, Issue 9, September 2020, bvaa090,
  16. Shigehara K, Izumi K, Kadono Y, Mizokami A. Testosterone and Bone Health in Men: A Narrative Review. J Clin Med. 2021 Feb 2;10(3):530. doi: 10.3390/jcm10030530. PMID: 33540526; PMCID: PMC7867125.
  17. Epidemiology and etiologies of male sexual dysfunction. (2022). UpToDate.
  18. Corona G, Isidori AM, Buvat J, Aversa A, Rastrelli G, Hackett G, Rochira V, Sforza A, Lenzi A, Mannucci E, Maggi M. Testosterone supplementation and sexual function: a meta-analysis study. J Sex Med. 2014 Jun;11(6):1577-92. doi: 10.1111/jsm.12536. Epub 2014 Apr 4. PMID: 24697970.
  19. Corona G, Rastrelli G, Di Pasquale G, Sforza A, Mannucci E, Maggi M. Endogenous Testosterone Levels and Cardiovascular Risk: Meta-Analysis of Observational Studies. J Sex Med. 2018 Sep;15(9):1260-1271. doi: 10.1016/j.jsxm.2018.06.012. Epub 2018 Aug 23. PMID: 30145097.
  20. Goodale T, Sadhu A, Petak S, Robbins R. Testosterone and the Heart. Methodist Debakey Cardiovasc J. 2017 Apr-Jun;13(2):68-72. doi: 10.14797/mdcj-13-2-68. PMID: 28740585; PMCID: PMC5512682.
  21. See CK, Turnbull D, Ritson F, Martin S, Tully P, Wittert G. Association of endogenous testosterone concentration with depression in men: a systematic review protocol. JBI Database System Rev Implement Rep. 2019 Sep;17(9):1894-1900. doi: 10.11124/JBISRIR-2017-004035. PMID: 30925504.
  22. Zarrouf FA, Artz S, Griffith J, Sirbu C, Kommor M. Testosterone and depression: systematic review and meta-analysis. J Psychiatr Pract. 2009 Jul;15(4):289-305. doi: 10.1097/01.pra.0000358315.88931.fc. PMID: 19625884.
  23. Corona G, Guaraldi F, Rastrelli G, Sforza A, Maggi M. Testosterone Deficiency and Risk of Cognitive Disorders in Aging Males. World J Mens Health. 2021;39(1):9-18. doi:10.5534/wjmh.200017
  24. Androgen deprivation therapy and risk of cognitive dysfunction in men with prostate cancer: is there a possible link? (2021, March 9). ScienceDirect.
  25. Lee DM, O’Neill TW, Pye SR, Silman AJ, Finn JD, Pendleton N, Tajar A, Bartfai G, Casanueva F, Forti G, Giwercman A, Huhtaniemi IT, Kula K, Punab M, Boonen S, Vanderschueren D, Wu FC; EMAS Study Group . The European Male Ageing Study (EMAS): design, methods and recruitment. Int J Androl. 2009;32(1):11–24
  26. Wu FC, Tajar A, Beynon JM, Pye SR, Silman AJ, Finn JD, O’Neill TW, Bartfai G, Casanueva FF, Forti G, Giwercman A, Han TS, Kula K, Lean ME, Pendleton N, Punab M, Boonen S, Vanderschueren D, Labrie F, Huhtaniemi IT; EMAS Group . Identification of late-onset hypogonadism in middle-aged and elderly men. N Engl J Med. 2010;363(2):123–135.
  27. Splansky GL, Corey D, Yang Q, Atwood LD, Cupples LA, Benjamin EJ, D’Agostino RB Sr, Fox CS, Larson MG, Murabito JM, O’Donnell CJ, Vasan RS, Wolf PA, Levy D. The Third Generation Cohort of the National Heart, Lung, and Blood Institute’s Framingham Heart Study: design, recruitment, and initial examination. Am J Epidemiol. 2007 Jun 1;165(11):1328-35. doi: 10.1093/aje/kwm021. Epub 2007 Mar 19. PMID: 17372189.
  28. Orwoll E, Blank JB, Barrett-Connor E, Cauley J, Cummings S, Ensrud K, Lewis C, Cawthon PM, Marcus R, Marshall LM, McGowan J, Phipps K, Sherman S, Stefanick ML, Stone K. Design and baseline characteristics of the osteoporotic fractures in men (MrOS) study–a large observational study of the determinants of fracture in older men. Contemp Clin Trials. 2005 Oct;26(5):569-85. doi: 10.1016/j.cct.2005.05.006. PMID: 16084776.
  29. Blank JB, Cawthon PM, Carrion-Petersen ML, Harper L, Johnson JP, Mitson E, Delay RR. Overview of recruitment for the osteoporotic fractures in men study (MrOS). Contemp Clin Trials. 2005 Oct;26(5):557-68. doi: 10.1016/j.cct.2005.05.005. PMID: 16085466.
  30. Lapauw BM, Taes Y, Bogaert V, Vanbillemont G, Goemaere S, Zmierczak H-G, De Bacquer D, Kaufman JM. Serum estradiol is associated with volumetric BMD and modulates the impact of physical activity on bone size at the age of peak bone mass: a study in healthy male siblings. J Bone Miner Res. 2009;24(6):1075–1085
  31. Lapauw BM, Taes Y, Bogaert V, Vanbillemont G, Goemaere S, Zmierczak HG, De Bacquer D, Kaufman JM. Serum estradiol is associated with volumetric BMD and modulates the impact of physical activity on bone size at the age of peak bone mass: a study in healthy male siblings. J Bone Miner Res. 2009 Jun;24(6):1075-85. doi: 10.1359/jbmr.081260. PMID: 19113912.
  32. Bhasin S, Pencina M, Jasuja GK, Travison TG, Coviello A, Orwoll E, Wang PY, Nielson C, Wu F, Tajar A, Labrie F, Vesper H, Zhang A, Ulloor J, Singh R, D’Agostino R, Vasan RS. Reference ranges for testosterone in men generated using liquid chromatography tandem mass spectrometry in a community-based sample of healthy nonobese young men in the Framingham Heart Study and applied to three geographically distinct cohorts. J Clin Endocrinol Metab. 2011 Aug;96(8):2430-9. doi: 10.1210/jc.2010-3012. Epub 2011 Jun 22. PMID: 21697255; PMCID: PMC3146796.
  33. Eskelinen S, Vahlberg T, Isoaho R, Kivelä SL, Irjala K. Biochemical reference intervals for sex hormones with a new AutoDelfia method in aged men. Clin Chem Lab Med. 2007;45(2):249-53. doi: 10.1515/CCLM.2007.042. PMID: 17311517.
  34. Sikaris K, McLachlan RI, Kazlauskas R, de Kretser D, Holden CA, Handelsman DJ. Reproductive hormone reference intervals for healthy fertile young men: evaluation of automated platform assays. J Clin Endocrinol Metab. 2005 Nov;90(11):5928-36. doi: 10.1210/jc.2005-0962. Epub 2005 Aug 23. PMID: 16118337.
  35. Tennekoon KH, Karunanayake EH. Serum FSH, LH, and testosterone concentrations in presumably fertile men: effect of age. Int J Fertil. 1993 Mar-Apr;38(2):108-12. PMID: 8097499.
  36. Boyce MJ, Baisley KJ, Clark EV, Warrington SJ. Are published normal ranges of serum testosterone too high? Results of a cross-sectional survey of serum testosterone and luteinizing hormone in healthy men. BJU Int. 2004 Oct;94(6):881-5. doi: 10.1111/j.1464-410X.2004.05051.x. PMID: 15476527.
  37. Salameh WA, Redor-Goldman MM, Clarke NJ, Reitz RE, Caulfield MP. Validation of a total testosterone assay using high-turbulence liquid chromatography tandem mass spectrometry: total and free testosterone reference ranges. Steroids. 2010 Feb;75(2):169-75. doi: 10.1016/j.steroids.2009.11.004. Epub 2009 Nov 17. PMID: 19925815.
  38. Haring R, Hannemann A, John U, Radke D, Nauck M, Wallaschofski H, Owen L, Adaway J, Keevil BG, Brabant G. Age-specific reference ranges for serum testosterone and androstenedione concentrations in women measured by liquid chromatography-tandem mass spectrometry. J Clin Endocrinol Metab. 2012 Feb;97(2):408-15. doi: 10.1210/jc.2011-2134. Epub 2011 Dec 7. PMID: 22162468.
  39. Yeap BB, Alfonso H, Chubb SA, Handelsman DJ, Hankey GJ, Norman PE, Flicker L. Reference ranges and determinants of testosterone, dihydrotestosterone, and estradiol levels measured using liquid chromatography-tandem mass spectrometry in a population-based cohort of older men. J Clin Endocrinol Metab. 2012 Nov;97(11):4030-9. doi: 10.1210/jc.2012-2265. Epub 2012 Sep 13. PMID: 22977273.
  40. Wong RMY, Wong H, Zhang N, Chow SKH, Chau WW, Wang J, Chim YN, Leung KS, Cheung WH. The relationship between sarcopenia and fragility fracture-a systematic review. Osteoporos Int. 2019 Mar;30(3):541-553. doi: 10.1007/s00198-018-04828-0. Epub 2019 Jan 4. PMID: 30610245.
  41. Harada N. Role of androgens in energy metabolism affecting on body composition, metabolic syndrome, type 2 diabetes, cardiovascular disease, and longevity: lessons from a meta-analysis and rodent studies. Biosci Biotechnol Biochem. 2018 Oct;82(10):1667-1682. doi: 10.1080/09168451.2018.1490172. Epub 2018 Jun 29. PMID: 29957125.
  42. Leslie SW, Siref LE, Soon-Sutton TL, et al. Male Infertility. [Updated 2022 Feb 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from:
  43. Epidemiology and etiologies of male sexual dysfunction. (2022). UpToDate.
  44. Corona G, Guaraldi F, Rastrelli G, Sforza A, Maggi M. Testosterone Deficiency and Risk of Cognitive Disorders in Aging Males. World J Mens Health. 2021 Jan;39(1):9-18. doi: 10.5534/wjmh.200017. Epub 2020 Apr 1. PMID: 32378366; PMCID: PMC7752509.
  45. Androgen deprivation therapy and risk of cognitive dysfunction in men with prostate cancer: is there a possible link? (2021, March 9). ScienceDirect.
  46. Zhang Z, Kang D, Li H. Testosterone and Cognitive Impairment or Dementia in Middle-Aged or Aging Males: Causation and Intervention, a Systematic Review and Meta-Analysis. J Geriatr Psychiatry Neurol. 2021 Sep;34(5):405-417. doi: 10.1177/0891988720933351. Epub 2020 Jun 30. PMID: 32602403.
  47. Traish AM. Testosterone and weight loss: the evidence. Curr Opin Endocrinol Diabetes Obes. 2014;21(5):313-322. doi:10.1097/MED.0000000000000086
  48. Vingren JL, Kraemer WJ, Ratamess NA, Anderson JM, Volek JS, Maresh CM. Testosterone physiology in resistance exercise and training: the up-stream regulatory elements. Sports Med. 2010 Dec 1;40(12):1037-53. doi: 10.2165/11536910-000000000-00000. PMID: 21058750.
  49. Vignozzi L, Corona G, Petrone L, Filippi S, Morelli AM, Forti G, Maggi M. Testosterone and sexual activity. J Endocrinol Invest. 2005;28(3 Suppl):39-44. PMID: 16042359.
  50. Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA. 2011;305(21):2173-2174. doi:10.1001/jama.2011.710
  51. Pilz S, Frisch S, Koertke H, Kuhn J, Dreier J, Obermayer-Pietsch B, Wehr E, Zittermann A. Effect of vitamin D supplementation on testosterone levels in men. Horm Metab Res. 2011 Mar;43(3):223-5. doi: 10.1055/s-0030-1269854. Epub 2010 Dec 10. PMID: 21154195.
  52. Isenmann E, Ambrosio G, Joseph JF, Mazzarino M, de la Torre X, Zimmer P, Kazlauskas R, Goebel C, Botrè F, Diel P, Parr MK. Ecdysteroids as non-conventional anabolic agent: performance enhancement by ecdysterone supplementation in humans. Arch Toxicol. 2019 Jul;93(7):1807-1816. doi: 10.1007/s00204-019-02490-x. Epub 2019 May 23. PMID: 31123801.
  53. Parr MK, Botrè F, Naß A, Hengevoss J, Diel P, Wolber G. Ecdysteroids: A novel class of anabolic agents?. Biol Sport. 2015;32(2):169-173. doi:10.5604/20831862.1144420
  54. Bhasin, S. (2021, February 15). JCI – Testosterone replacement in aging men: an evidence-based patient-centric perspective. The Journal Of Clinical Investigation.
  55. Park HJ, Ahn ST, Moon DG. Evolution of Guidelines for Testosterone Replacement Therapy. J Clin Med. 2019;8(3):410. Published 2019 Mar 25. doi:10.3390/jcm8030410
  56. Twitchell DK, Pastuszak AW, Khera M. Controversies in Testosterone Therapy. Sex Med Rev. 2021 Jan;9(1):149-159. doi: 10.1016/j.sxmr.2020.09.004. Epub 2020 Dec 9. PMID: 33309270.
  57. Dubin, J.M., Fantus, R.J. & Halpern, J.A. Testosterone replacement therapy in the era of telemedicine. Int J Impot Res (2021).
  58. Skinner JW, Otzel DM, Bowser A, Nargi D, Agarwal S, Peterson MD, Zou B, Borst SE, Yarrow JF. Muscular responses to testosterone replacement vary by administration route: a systematic review and meta-analysis. J Cachexia Sarcopenia Muscle. 2018 Jun;9(3):465-481. doi: 10.1002/jcsm.12291. Epub 2018 Mar 15. PMID: 29542875; PMCID: PMC5989848.
  59. Borst SE, Yarrow JF. Injection of testosterone may be safer and more effective than transdermal administration for combating loss of muscle and bone in older men. Am J Physiol Endocrinol Metab. 2015 Jun 15;308(12):E1035-42. doi: 10.1152/ajpendo.00111.2015. Epub 2015 Apr 21. PMID: 25898953; PMCID: PMC6189635.
Table of Contents
    Add a header to begin generating the table of contents