Testosterone! What is it? What does it do? What happens to it?
Testosterone is a hormone that affects a surprisingly large number of bodily functions. It plays a significant role in the overall health of both sexes, yet women only produce about 5 – 10% of the testosterone that men produce. It’s generally considered to be the male hormone. It’s what makes a man, a man.
OK, but what is testosterone? Let’s get some of the basic terminologies out of the way. Testosterone is a steroid hormone. Steroids are a class of compounds with a very specific molecular structure, usually 4-6 carbon rings. And a hormone is a signaling molecule that exerts influence on other organs of the body. But in the case of testosterone, we can say that it influences everything in the body. Testosterone is a sex steroid, which is also known as gonadocorticoids and gonadal steroids.
There are 3 types of sex steroids: androgens, estrogens, and progestogens. Androgens regulate the development and maintenance of male characteristics, while estrogens perform the same function on female characteristics. Testosterone is the primary androgen, and estradiol is the primary estrogen.
The primary role of progestogens is in the female reproductive system, and they have little to no role in feminization. As men grow older, their testosterone production peaks at about age 30 and, after the age of 40, begins to decline at a rate of about 1.6% per year. Given the number of bodily functions that are impacted by testosterone, a lot of the aspects of aging can be attributed to low testosterone.
So, what exactly are these functions that can be impacted by T? Well, they are broken down into two main categories: anabolic, or the repair and regeneration of tissue, and androgenic, which is the development of male sex characteristics.
The anabolic functions of testosterone are essentially building functions. So it controls muscle mass, it affects how much fat your carrying in your body, it controls bone mass, it impacts heart health, it affects your energy levels, it plays a role in the production of red blood cells, and it improves agility.
The androgenic functions of testosterone are those functions that promote male characteristics, including maintaining the reproductive system, sustaining sperm development and fertility, increasing libido and erectile function, it controls the register of your voice, and maintains the growth of body and facial hair.
Testosterone also has some psychological aspects. It can impact cognitive function. It affects your mood, your sense of self-esteem, and your self-confidence and competitiveness. That’s a lot of stuff!
OK, so how is it produced in the body? While small amounts are produced in the adrenal glands, which sit on top of the kidneys and even in our skin.
The lion’s share of the test is produced in the testicles. The whole process is kicked off when the hypothalamus detects that we need more T and secretes a hormone called gonadotropin-releasing hormone (GnRH). This hormone travels to the pituitary gland, located in the back of our brain.
When the pituitary gland detects GnRH, it starts secreting 2 hormones, known as gonadotropins, into the bloodstream. These 2 hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), travel down to the testicles. This whole hypothalamus, pituitary, testicle, or gonad, pathway is called the hypothalamic-pituitary-gonadal axis, or HPG.
Upon arriving in the testicles, the FSH starts producing more sperm, and the LH stimulates the Leydig cells in the testicles to create more testosterone. When testosterone is made in the human body, it is synthesized from another compound, known as a precursor. And the precursor for testosterone is cholesterol.
Testosterone is synthesized directly from cholesterol. That’s the good cholesterol, known as HDL cholesterol, or high-density lipids. The Leydig cells can convert cholesterol into testosterone, and if there’s not enough cholesterol in our blood, the testicles can create a bit more of it. But relying too heavily on cholesterol produced by the testicles can actually inhibit the production of testosterone in the Leydig cells. Once testosterone is produced, it goes back into the bloodstream.
When the hypothalamus detects that we have enough testosterone in the bloodstream, it signals the pituitary gland to stop LH production, and the testicles ramp down T production. Testosterone comes in a few different flavors, and only one of them is bioavailable, meaning in a form that we can use. On average, a man’s body produces about 7 mg of testosterone a day.
Almost immediately, about 40 to 65% of that testosterone is bound to a protein called sex hormone-binding globulin (SHBG). SHBG is produced in the liver and plays an important role in regulating the amount of free testosterone circulating through the bloodstream. Testosterone that is bound to the SHBG protein is biologically inactive, meaning that it’s unavailable to our bodies for building muscles or any of the other myriad ways that T is used. Another 30 – 35% of the testosterone in our system is bound to another protein called albumin.
Like SHBG, this protein is also produced in the liver, and its function is to stabilize extra-cellular fluid volumes. And like SHBG, albumin-bound protein is biologically inactive. However, unlike SHBG-bound testosterone, the bind between albumin and T is weak and can be easily broken in order to free up more testosterone as needed.
And finally, we get to free-testosterone. This is the stuff that works all the magic. It’s pure testosterone that isn’t bound to any proteins, and it’s the only testosterone that is bio-available to our bodies. Free testosterone can enter cells and activate receptors that will man you up and perform all of its wonders on your mind and body. But it only makes up about 2% to 3% of the total testosterone in the system. Because it constitutes such a tiny fraction of the total T, it’s relatively difficult to measure accurately. Now, a man’s body begins to produce less and less testosterone after the age of 30, between 1% and 1.6% less each year.
As a man starts to approach his 50’s, 60’s and 70’s, his testosterone levels can start to get really low, and this process is called andropause, kind of like menopause in women, except that it’s not a sudden decrease in hormones happening over a few months. It can and does take years, decades even, and is therefore much more insidious.
Once a man enters andropause and has low testosterone, the effects are essentially the opposite of what the effects of testosterone are. There’s an overall decrease in muscle mass and strength, bone density, erectile function and libido, red blood cells, and a sense of well being and cognitive function. They all decline. There’s also a change in body composition and an increase in body fat.
Testosterone levels for the average man have been declining for the last 2 or 3 generations. Researchers in the US are finding that testosterone levels are substantially lower than they were 15 years ago by about 15 to 20%. In Scandinavia, studies show that a 35-year-old man born in 1970 had about 20% less testosterone than a man of his father’s generation at the same age. And this from an article written in 2007. So it’s already gotten much worse.
Men’s virility has been in decline since WWII, and we believe that nutritional and lifestyle changes, along with the presence of every more prevalent toxins in our environment, is to blame. That’s a pretty gloomy picture for modern, aging men. But hope is not lost. It is possible to boost your testosterone production to achieve optimal test levels, not average test levels but optimal test levels. And it is possible to do this naturally, without hormone supplementation and all the risks that entail.