January 6, 2023

Testosterone is a hormone found in all humans – male and female. However, males have much higher amounts of testosterone than females when healthy. The testicles make this hormone in males, while the ovaries make it in much smaller amounts in females. 

While you need testosterone to stay healthy, the exact amount your body makes varies widely throughout your life. Testosterone increases a lot during puberty but decreases after age 30. This causes several health effects that aren’t always good. 

Let’s take a further look at what testosterone is, what it does, and how it may impact your health. 

What is Testosterone?

Simply put, testosterone is a hormone. Hormones are chemicals that tell your body what to do. Therefore, your body may not do what it’s supposed to without proper testosterone levels. In males, testosterone is directly tied to the development of male sexual characteristics. 

In other words, it’s what makes a man a man. 

However, women also produce testosterone to a much lower extent. In women, testosterone does much of the same things it does in males, such as controlling bone density and muscle strength. Still, it doesn’t play the significant reproductive role for women that it plays for men. 

How is it Produced?

In males, testosterone is produced by the testicles. Specifically, it is produced by special Leydig cells in the testicles – primarily, at least. In women, the ovaries produce testosterone. This isn’t surprising since the ovaries also produce a range of other hormones. 

While males make testosterone in the testicles, the amount of testosterone created is controlled by the brain and pituitary gland (found in the brain). This part of the brain tells the testicles how much testosterone to produce, which they then do to the best of their ability. 

However, there are several parts where this process can mess up. The message from the brain to the testicles can get lost, or the testicles may be unable to produce the proper amount. 

Let’s break down the role of testosterone by looking at its impact on our bodies.

1. Maturation and Development

Testosterone levels increase rapidly during puberty when it is involved in the development of several male features. During this time, males become fertile mainly because of the increased testosterone. After 30, it’s normal for a male’s testosterone to drop a bit each year (and it’s not necessarily a bad thing).

Technically, males produce more testosterone than females shortly after birth – around seven days after. This increase helps form the male genitals, of course. However, it also affects the brain and other systems. 

For instance, testosterone changes during puberty and directly impacts the male (and femal) developing brain. Therefore, this hormone literally changes how a male thinks during puberty. 

However, this relationship is very complex. We know a bit about how testosterone affects development, but we are still learning more. 

2. Libido Regulation

Testosterone has a significant impact on sexuality. Therefore, it only makes sense that it would impact libido. However, this relationship goes two ways. While higher testosterone often leads to increased sexual desire, sexual activity increases testosterone. Therefore, it’s a bit of a double-whammy effect. There is some evidence that testosterone works as a “use it or lose it” system in this regard. 

Low libido is often known as a sign of low testosterone. However, patient reports of low libido aren’t always lined up with low testosterone. Studies have found that relying on these self-reports alone is hit-or-miss

This confusion is likely due to the many factors that affect libido. Furthermore, because there is a bit of a give-and-take relationship, lower libido may lead to low testosterone due to a different underlying reason. Therefore, many doctors face a chicken-or-the-egg conundrum. It’s hard to tell if the libido was caused by low testosterone or led to low testosterone. 

3. Sperm Production

Men have to make a certain amount of quality sperm to be fertile. Many things affect sperm, but testosterone is one of the few factors that is very significant. If you have low testosterone, your sperm is likely affected. 

However, this does not mean that taking extra testosterone will make you more fertile. In fact, the opposite is true. The testosterone concentration is highest in the testicles, where it is created. This fact means sperm is exposed to very high testosterone concentrations.

When males are given a testosterone supplement (which only enters the blood), the body often stops producing as much testosterone to compensate. For this reason, the male’s blood testosterone will rise, and the concentration in his testicles may fall. This cycle leads to sperm being exposed to less testosterone as it develops.

There are now many studies involving the contraceptive effects of testosterone supplements. While testosterone may be necessary for sperm development, testosterone therapy limits fertility. 

4. Muscle Development

Testosterone is directly linked to muscle development in both males and females. Therefore, many men who take excessive amounts of synthetic testosterone are often concentrated on building muscle. As men age, building muscle may be harder due to lower testosterone. 

This hormone increases muscle growth because it increases neurotransmitters. To put it simply, it enables the muscles to perform at a higher rate, making them grow faster. Testosterone also plays a role in protein synthesis, which is necessary to develop muscles. This should make it apparent that testosterone plays a significant role in muscle building in more ways than one. 

However, that doesn’t mean that every male needs to run out and take testosterone to get jacked. Increasing blood testosterone when your testosterone isn’t low can negatively affect fertility, mood, and other parts of your life. Excessive testosterone can be just as bad as low testosterone. 

5. Bone Growth and Density

Testosterone also makes bones grow thicker, decreasing the chances of fractures. This factor is one reason older individuals may be more likely to break bones; their T-levels are often lower than younger individuals. 

Simply put, this hormone increases bone growth, which translates to density in adults. You can thank this mechanism for those crazy puberty growth spurts, too. Testosterone also tells the bone marrow to make red blood cells. 

Therefore, men with low T often have an increased chance of fractures. However, because bones become brittle over time, you often have to have low-T for a very long time before the bones become noticeably brittle. 

Similarly, the red blood count may be low in men with deficient testosterone. Without testosterone encouraging the production of red blood cells, the body may not make enough. 

6. Mood Regulation

While it is less known than the other effects, testosterone also plays a role in mood regulation. Of course, human mood is hard to study and we know less about this effect than others. 

Testosterone can affect a male mood in many ways. For instance, it is tied to aggression and competitiveness. However, it may also increase self-esteem. Some men may become depressed when their T-levels are too high or too low. That said, there is no evidence that all men become depressed when their T-levels are off. 

In some cases, lower testosterone can also lead to other effects on the man’s life, sleep problems being one of those effects. In the end, these can lead to decreased mood, as well. 

While testosterone does play a role in mood, it isn’t the only factor by any means. Someone’s mood is a very complicated thing. 

7. Body Hair Growth

During puberty, males grow facial hair and more hair in general due to their increased testosterone. As a man’s testosterone increases, his body hair growth also increases. (Strangely enough, high testosterone has the opposite effect on women.)

Furthermore, when a man’s testosterone decreases, he may also find his body hair decreasing. Therefore, men may lose hair when they age, but the effect isn’t always significant—many men age with lowering testosterone without losing hair. 

Men with very high testosterone may have increased or decreased hair growth. However, that doesn’t mean you can use testosterone gel to reverse balding. Testosterone and hair growth has a bit of a complicated relationship. Too much testosterone can lead to an increase in DHT, which is often linked to balding. 

Therefore, taking testosterone to prevent balding isn’t recommended. It can very quickly have the opposite effect. Still, in case of low testosterone getting a boost may help with normalazing hair growth.

8. Weight Regulation

Testosterone affects muscle growth, which we’ve already discussed. Increased muscle mass also increases the number of calories your body burns. Since it also plays a role in fat burning, it isn’t a giant leap to claim that testosterone helps with weight regulation. 

While this is likely true to some extent, the evidence is much more complicated. Overweight men often have less testosterone so we’re stuck with another what-came-first question. Is it low testosterone that leads men to become overweight? Or is it the excess weight that led to the low testosterone?

Of course, if someone becomes obese and the excessive weight drops his T-levels, it will be much harder for him to lose weight. From a practical standpoint, what came first doesn’t matter much when trying to lose the weight you’ve already gained. 

There is evidence that obese men are more likely to lose weight and keep it off with testosterone therapy. However, this should only be done in men with low testosterone. Having excessive levels wouldn’t necessarily increase the amount of weight you’d lose. 


Testosterone plays a significant role in a man’s body. While it does affect sexuality and muscle mass, it can also affect mood, weight regulation, sperm production, and bone density. If a man’s testosterone levels are not typical, it can cause many health issues. 

Therefore, testing testosterone can be vital in determining the cause behind specific symptoms and conditions. 

About the Author Tim Rockwell

Tim Rockwell is a highly skilled and knowledgeable fitness expert. With a background in exercise science and years of experience in the fitness industry, Tim is passionate about sharing his expertise with others through his writing. He currently contributes articles to Eurasc, where he shares practical tips and strategies for leading a healthy, active lifestyle.

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