Low testosterone in men takes a toll on your energy levels, well-being, heart health, and love life.

Worldwide, 10-40% of men suffer from testosterone deficiency, and many of them receive no diagnosis or treatment[1][2]. It’s more common in older men, but plenty of young men have low testosterone levels, too.

In this article, you’ll learn about the two types of testosterone deficiency, what causes them, and how to prevent your T levels from dropping in the first place.

What is Testosterone Deficiency?

Low testosterone means testosterone below the normal range.

A man with less than 300 ng/dL testosterone has low testosterone. Some men may also experience symptoms of low T if their levels drop below 500 ng/dL[3].

Symptoms of low testosterone in men include[4]:

  • Depression
  • Decreased muscle mass
  • Loss of vigor
  • Fatigue
  • Lower libido
  • Erectile dysfunction
  • Infertility

There are two different types of testosterone deficiency. And while both of these issues result in low testosterone in men, each occurs for different reasons.

Secondary hypogonadism refers to low testosterone caused by the hypothalamus, pituitary gland, or hormones like estrogen. In men with secondary hypogonadism, their brains or hormones are out of balance, but their testes can still produce testosterone.

Primary hypogonadism means low testosterone caused by testicular problems. Because the testes are unable to make testosterone, this type of deficiency can only be treated by testosterone replacement therapy (TRT). It is rarer and more difficult to treat than secondary hypogonadism.

Read on to learn the causes of secondary and primary hypogonadism and how you can reduce your risk of low testosterone.

The 6 Most Common Causes of Low Testosterone in Men

#1: Testicular Damage

If your testes are damaged, they can’t make testosterone. As a result, you’ll experience symptoms of low T like irritability, depression, loss of muscle mass, and low libido.

This type of testosterone deficiency is called primary hypogonadism. It’s the least common type and can only be treated with testosterone replacement therapy (TRT).

Damage results from testicular cancer, inflammation, poor diet, or cellular stress. Here’s how to avoid it:

  • Perform self-exams of your testicles each month–ask your physician if you don’t know how.
  • Avoid overheating your testes in hot tubs.
  • Never carry your cell phone in your pants pocket.
  • Don’t use a laptop in your lap.
  • Wear an athletic cup during contact sports.
  • Avoid processed foods, refined carbohydrates, and trans fats.

If your blood tests show low testosterone with high levels of LH and FSH, it may be primary hypogonadism. Your doctor or endocrinologist can run more tests so you know for sure.

Should you receive a diagnosis of primary hypogonadism, ask your doctor about TRT.

#2: Excess Body Fat and High Estrogen

If you don’t have testicular damage, you have secondary rather than primary hypogonadism. That means your testes are capable of making testosterone, but they aren’t receiving signals from your body to create it.

High body fat levels are one of the most common causes of low T due to secondary hypogonadism[5].

Men who are overweight tend to have higher estrogen levels. This is because fatty tissue produces an enzyme called aromatase that converts testosterone (the male hormone) into estrogen (the female hormone)[6].

Therefore, you “lose” testosterone as it converts to estrogen. Not only that, estrogen also acts as a “stop” signal that tells your body to make less testosterone. As a result, your production slows down, and your T levels drop.

Fortunately, research shows this condition is reversible[5][7]. By losing weight and getting healthier, you can lower your estrogen and boost your T levels.

If you lose the weight but your testosterone doesn’t increase, you can talk to your doctor about clomiphene or anastrazole. Short-term use of clomiphene can reverse low T after weight loss, while anastrazole inhibits aromatase to reduce estrogen levels, which also helps boost testosterone[8][9].

Under no circumstance should you attempt to treat low testosterone on your own using prescription drugs. Clomiphene and anastrazole are safe under medical supervision, but can make the problem worse if you don’t know what you’re doing.

#3: Low Vitamin D Levels

Your body needs vitamin D to make testosterone. So if you have a vitamin D deficiency, you’re also more likely to suffer from low testosterone.

One study of obese men with low testosterone discovered that over 90% of them also had low vitamin D levels[5].

Evidence shows that raising vitamin D levels can help reverse hypogonadism in nearly half of men[10]. And other research shows that taking approximately 3000 iu of vitamin D daily for a year increases men’s T levels by 30%[11].

The best way to obtain vitamin D is through direct sun exposure, but it’s clear that vitamin D supplements are also helpful to reverse low testosterone in men.

#4: Stress and Aging

In the past, doctors thought men’s testosterone levels declined due to aging. They called it “andropause.” This theory is no longer accepted, because unlike women, sex hormones in men don’t always drop off as men age[12].

Research now shows that while many men do have lower T the older they get, some men never experience low testosterone, even in their later years[13].

Why would testosterone levels decline in some men with age, but not others? The most likely answer is stress.

Studies show that any form of stress–like exams, hunger, lack of sleep, or job stress–instantly lowers testosterone levels in men[14][15][16]. Illness and surgery can also have the same effect[17]][18].

As you age, chronic stress can lower your T levels over time. Eventually, they stop bouncing back and you are stuck with low testosterone. But in men who aren’t stressed out, or who handle stress well, testosterone can remain relatively high for life.

Scientists discovered that in older men with health problems, testosterone deficiency was over 15 times more likely compared to healthy men the same age[19].

The takeaway? If you manage your stress levels and look after your health you can have healthy testosterone levels for life.

#5: Traumatic Brain Injury Causes Low Testosterone in Men

Concussions and head trauma are another cause of low testosterone in men.

Because your hypothalamus and pituitary are inside of your skull, brain injuries can prevent them from releasing signaling hormones that tell your body to release testosterone[20].

Sometimes it only lasts a few weeks, but in other cases the decrease can last for 3-6 months. And occasionally, it’s permanent[21][22].

If you’ve hit your head or played high-impact sports like boxing or football, it’s a good idea to have your testosterone levels checked just to be on the safe side. This is especially true if you have symptoms of low T.

#6: Anabolic-Androgenic Steroids and Supplements

Anabolic-androgenic steroids (AAS) are synthetic versions of male hormones. They’re sold in injectable as well as oral preparations.

Some men use AAS for bodybuilding, to gain muscle mass, or to enhance athletic performance.

Unfortunately, along with side effects like liver damage, acne, and gynecomastia (breast tissue growth), AAS can also cause low testosterone in men[23].

When you use steroids, they shut off your body’s natural testosterone production within several weeks[24]. Over time, your testes shrink because they’re not in use[25]. And even after you stop, there’s no guarantee your levels will rise on their own[26].

In some cases this leads to long-term dependence on steroids, and in others the result is low testosterone after stopping usage.

However, case studies show that the drug clomiphene, given under medical supervision, can sometimes reverse these effects[27][28].

It’s better to avoid steroids altogether, but if you’ve used them in the past, your best bet is to see your doctor for an appointment to have your levels checked and discuss treatment options. While a visit about prior steroid use can seem embarrassing, you’ll be much better off dealing with the issue directly.

Final Thoughts

If you think you have low testosterone, talk to a trusted physician first. The main symptoms–like fatigue, irritability, and erectile dysfunction–can also be caused by other health problems.

And if you do have a testosterone deficiency, the next step is to determine if it’s primary (from the testes) or secondary (due to hormone imbalance, head injury, or other non-testicular causes).

Low T is not an inevitable consequence of aging, and it’s highly treatable. There’s a good chance you can boost your levels by losing body fat, raising your vitamin D levels, reducing stress, and maintaining a healthy lifestyle.

But if your testosterone levels don’t respond to lifestyle changes, talk to your doctor about other treatment options. TRT is a last resort and is usually only required for men with testicular damage.