Contrary to what many men think, testosterone controls so much more than just the body’s sexual function. It plays a vital role in muscle growth, metabolism, behavior, and even cognitive processes like memory and focus.
Testosterone is one of the main androgens in the body, a group of compounds also known as male sex hormones. Among other things, testosterone is responsible for the proper development of the male reproductive system and secondary sexual characteristics like body hair, voice deepness, body fat distribution, and increased bone and muscle mass.
In addition to promoting the development of male sexual organs and characteristics, testosterone also activates the androgen receptors in muscle and skeletal tissue. When these receptors are triggered, they initiate protein synthesis in the muscles and increase the mineral uptake in the bones. The end result of these processes is increased muscle mass and bone density.
Around 95% of the testosterone in the male body is produced in the Leydig cells of the testicles. The remaining 5% is synthesized by the adrenal glands, a pair of organs sitting just above the kidneys. In women, testosterone is produced in the ovaries and in the adrenal glands—although, of course, in much lesser amounts than those in men.
The whole process of testosterone production starts in the brain’s hypothalamus. It releases a hormone known as the gonadotropin-releasing hormone (GnRH). This hormone triggers receptors in the pituitary gland that causes it to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH) into the bloodstream. When the luteinizing hormone makes it to the testicular Leydig cells, it prompts the cell to convert cholesterol to testosterone—specifically, free testosterone.
Once free testosterone is produced, it enters the bloodstream to get to various parts of the body. Free testosterone interacts with androgen receptors all around the body, in all cells that have this kind of receptors.
As the name suggests, free testosterone is free for the body to use. But, free of what, exactly?
Sex hormones like testosterone, estrogen, and dihydrotestosterone can be bound by certain proteins and become incapable of activating their respective receptors in cells. These proteins are called sex hormone-binding globulins (SHBG).
SHBG is produced in the liver and helps to regulate one's levels of androgens in puberty. After puberty, SHBG levels normally decline. However, this is not always the case—and that's one of the potential causes of low testosterone levels.
Like with any other hormone, when testosterone levels are not at their optimum, all sorts of negative effects may arise. For example, low testosterone levels may increase the risk of developing obesity metabolic syndrome, type 2 diabetes, depression, and prostate cancer.
With these potential consequences, it can be tempting to take synthetic medications (anabolic steroids, for example) to boost your testosterone levels. However, by filling up your body with testosterone from external sources, you force your body to dial down its natural production of testosterone. The logic is simple: if there's enough testosterone already, there's no point in producing more of it. In physiology, this principle is called a negative feedback loop and its main purpose is to prevent excess—excess hormone production, excess reflexes, excess anything.
Back to the matter at hand. When you stop taking exogenous testosterone, your body won't switch to making its own testosterone instantly. For some time, it won't produce any testosterone at all, as if lagging in its response to the new situation. As if that wasn't enough, using synthetic anabolic steroids causes a wide range of other side effects. These include high blood pressure, gynecomastia, abnormal behavior, and increased risk of cancer.
That's why the best way to increase testosterone levels is through natural means. Some of these natural strategies include: having a diet high in healthy fats, getting enough vitamin D3 and zinc from foods and supplements, and regular exercise.