However, men who are going through "the change" can experience symptoms, too.
Low testosterone, or "Low T," may be happening earlier and more often than expected.
As the body ages, hormone variations are normal, but when is it time to take action in men?
Low testosterone is estimated to affect up to 5 million men and can cause a host of mental and physical symptoms.
The uncertainty is whether it is a medical condition needing treatment or something men should learn to live with.
The symptoms in Michael Andruzzi were subtle.
"Lethargic, no energy - zero," said Andruzzi.
Only in his late 30's at the time, the fit and muscular Andruzzi knew something was up.
"To go to the gym was very difficult because just very tired, and just didn't feel like going. No motivation," said Andruzzi.
Not exactly signs of something life threatening, but Andruzzi mentioned the symptoms to his urologist at Northwestern Memorial Hospital.
Blood tests were done, and Andruzzi was shocked to learn he had extremely low levels of testosterone. Low testosterone can affect men of various ages.
Urologist Robert Brannigan of Northwestern Memorial Hospital thinks low testosterone, also known as hypogonadism, is under-diagnosed.
Part of the problem he says is many men with the condition don't recognize the symptoms.
They include low energy or fatigue, weight gain, reduced muscle mass or strength, decreased sex drive and mood swings.
"Depression is actually something that closely parallels or mimics low testosterone," said Brannigan. "So we see many men who have actually been treated clinically with antidepressants when in turn their underlying problem is low testosterone."
In many ways, testosterone is what makes men men, but as the body reaches middle age, levels will slowly drop by an estimated average of 1-2 percent per year.
Many are never really bothered by the change, but others can have problems.
Researchers are still trying to understand the long term health effects of low testosterone.
A rise in cases of low testosterone has some researchers scratching their heads.
"What we found which is interesting is that younger men have a much higher chance of having low testosterone then we thought about before," said Craig Niederberger of the University of Illinois at Chicago.
The reasons remain unclear, and what to do about it is also debatable - to learn to live with it or to take action.
Testosterone replacement therapy comes in many forms including patches, gels, implants and injections.
The marketing of these medications has exploded, but a recent medical journal review says treatment is questionable because it has risks and its efficacy is uncertain.
Brannigan says when taken in the prescribed doses, these treatments are generally safe and effective, but he stresses the therapy is not appropriate for all patients.
"For the patient where it's really interfering with the quality of life, I think sitting down with doc and having a discussion makes a lot of sense," said Brannigan.
Mike Andruzzi says treatment has changed his life. He has been doing testosterone replacement for a couple years now to help bring his levels to a more normal range. He says his energy level is up and so are his spirits.
"It doesn't make me feel better than the average person," said Andruzzi. "It makes me feel like the average person."
Guidelines were just revised on sex hormone treatments. The guidelines recommend against screening the general population.
The guidelines also say doctors should only make a diagnosis of low testosterone in men with consistent symptoms and signs and clear measurements of low levels.
Dr. Robert BranniganAcademic Office
Northwestern University, Feinberg School of Medicine
Department of Urology
303 East Chicago Avenue, Tarry 16-703
Chicago, IL 60611-3008
Fax (312) 695-7030
675 North Saint Clair Street, Galter 20-150
Chicago, IL 60611-2927
Fax (312) 695-7030
Dr. Craid Niederberger
UIC Medical Center