If you had asked a doctor 10 years ago about bumping testosterone into the high-normal range to enhance one's physique, chances are slim you would have gotten a positive response. "Testosterone is bad for you, " he would probably say. "It will shrink your grapes to raisins, give you liver disease and make you backhand your Grandma!"
Enter 1996 and the legal availability of androstenedione (a-dione) and other prohormones. For the first time, "steroids" were legally available over the counter and testosterone became user-friendly. It could not only enhance strength and muscle size, but also improve body composition, bone density, libido, and immunocompetence. Some research even suggested T could make you smarter! Unfortunately, as supplement sales skyrocketed, so did marketing hyperbole. And so, too, did the bull about which company had the most potent prohormone concoction and how effective these "legal steroids" were.
If you are tired of being confused by "diones", "diols" and "19-nor" something-or-others - and want to know the real benefits and risks associated with testosterone boosting - read on. The information presented may just clear some of that fog in your noggin'.
Testosterone is a 19-carbon steroid hormone produced primarily by the Leydig cells of the testes (in men) and the ovaries (in women). Smaller amounts are produced in the adrenal glands of both sexes. As a "steroid", testosterone belongs to the androgen class of hormones that also includes dihydrotestosterone (DHT), dehydroepiandrosterone (DHEA), androstenedione, and androstenediol. Six other classes of steroid hormones exist, including estrogens (the bane of male bodybuilders), progestins (some female contraceptives are made of these), mineralocorticoids (which help control water balance), glucocorticoids (mainly anti-inflammatory compounds), vitamin D, and bile acids.
In men, approximately seven mg of testosterone is produced each day, and blood levels range between 300 and 1000 ng/dL (10-28 nmol/L). Females, on the other hand, produce about 1/15th of this amount, leading to average blood levels of only 25 to 90 ng/dL (1-2.5 nmol/L). All steroid hormones are derived from the sterane ring structure, composed of three hexane (6 carbon) rings and one pentane (5 carbon) ring.
In healthy humans, the "rate-limiting" step in testosterone biosynthesis is the conversion of cholesterol into a hormone called pregnenolone. This hormone is then first converted to either DHEA or progesterone before being further degraded in a stepwise fashion to testosterone. Schematically, the two possible pathways look like this: (Enzymes have been omitted for clarity.)
Cholesterol » pregnenolone » progesterone » androstenedione »
Cholesterol » pregnenolone » DHEA » androstenediol »
After testosterone is secreted into the bloodstream, 96-98 percent is bound to proteins called albumin and globulin. This binding is thought to serve three purposes: 1) it makes testosterone soluble for transport within the blood, 2) it protects testosterone from degradation by the liver and kidneys, and 3) it serves as a reservoir or storage depot that can be used to dampen fluctuations in plasma testosterone.
The two to four percent not bound to plasma proteins is known as "free testosterone" and is thought to represent the biologically active fraction of the hormone; in other words, the amount that is capable of interacting with cells to cause physiological changes. And although recent data suggest this is most likely an oversimplification, we'll leave that discussion for another time.
Regulation of testosterone levels is governed by two factors: the total amount of testosterone in the blood, and the binding capacity of the plasma proteins. Obviously, as binding capacity goes up blood levels of free testosterone go down. Not surprisingly, certain drugs (anabolic-androgenic steroids, insulin, etc.) and perhaps nutritional supplements (like avena sativa, urtica dioica, etc.) can reduce the binding capacity of the blood and result in higher free-testosterone levels. (Editors' Note: Nutrition is also a factor in testosterone regulation; see our March discussion on this topic in Experiments vs. Experience.)
There is also mounting evidence that some types of pollution and pesticides can do the opposite. So much for running sprints in downtown Detroit! Also, testosterone production from the testes occurs the entire period of fetal development until about 10 weeks after birth. Then the gears screech to a stop until puberty - a time when men know all-too well their T levels are screaming.
This is a time when young men really blow past their female counterparts in body weight and muscularity - and get drawn toward sports like high school football, along with other aggressive pastimes. Sadly in many ways, testosterone levels begin to decline between the third and fourth decade of life. And by 80 (if we make it that long) we are only one-third the man we used to be, testosterone-wise.