Low levels of the sex hormone testosterone — commonly referred to as "low T" — have been blamed for a host of health conditions, ranging from depression to increased breast size in men.
And because low T can be treated with prescription medication, it has become the health problem du jour for aggressive pharmaceutical marketing: The airwaves are now flooded with ads showing doughy, middle-age men turning into vigorous athletes and confident lovers.
Is low T a real condition that needs medical treatment — despite the potential risks associated with testosterone therapy — or is it just a pharma sales rep's dream come true? The answer may lie in determining what exactly constitutes a low testosterone level. [Macho Man: 10 Wild Facts About His Body]
What causes low T?
Testosterone is produced by a man's testicles and is key to the development of male sex organs, bone density, muscle mass and secondary sex characteristics such as facial and body hair. Women's ovaries also produce small amounts of testosterone, as do the adrenal glands, according to the National Institutes of Health (NIH).
Low levels of testosterone — referred to as hypogonadism by hormone specialists — can result from injury to the testicles, diseases including testicular cancer and mumps, certain drugs or therapies such as chemotherapy and radiation treatment.
The single greatest cause of low T, however, is the simple act of aging: Testosterone levels peak during adolescence and early adulthood. As a man ages, his testosterone levels drop about 1 percent each year after age 30, according to the Mayo Clinic. [7 Ways the Mind and Body Change With Age]
Given that fact, it's not surprising that the "normal" range for testosterone levels is quite broad: Doctors generally consider any level between 300 and 1,000 nanograms per deciliter (ng/dl) an acceptable blood level of testosterone for an adult male.
But there's disagreement over how low is too low, and how much importance to place on testosterone levels versus other symptoms. Meanwhile, health experts are alarmed at the rapid increase in hormone therapy among men: Between 2001 and 2011, the use of hormones among men over 40 increased by almost 360 percent, according to a 2013 report in the Journal of the American Medical Association.
And the criteria for determining if a man is suffering from the symptoms of low T are also broad: Any man who has a decreased sex drive, a lack of energy, a drop in strength or endurance, less enjoyment of life, decreased athletic ability, depression or anger — in other words, all the hallmarks of middle age — may think after watching a low-T commercial that he could be a candidate for hormone therapy.
"Those symptoms are true of everybody as they age, to a greater or lesser extent," Glenn Braunstein, an endocrinologist at Cedars-Sinai Medical Center in Los Angeles, told the Washington Post. As a result, testosterone therapy — often in the form of convenient skin patches or lotions — has been used in men with acceptable levels of testosterone.
"We're giving people hormones that we don't know they need, for a disease that we don't know they have, and we don't know if it'll help them or harm them," Dr. Lisa Schwartz, a professor at the Dartmouth Institute for Health Policy and Clinical Practice, told The New York Times.
Hormone therapy risks
Though testosterone therapy is generally well-tolerated by most men, there are risks, including polycythemia (a high blood cell count that can increase the risk of stroke and heart attack), infertility and prostate cancer.
And there's a dearth of studies into its long-term effects. "For a drug, testosterone's relatively safe," John Morley, an endocrinologist at St. Louis University School of Medicine, told the Post. "But no studies go longer than three years. What happens if you take it for 20 years?"
Concerns over the long-term impacts of testosterone therapy have prompted the Food and Drug Administration (FDA) to take action: Last week, the agency issued a press release announcing it was "investigating the risk of stroke, heart attack and death in men taking FDA-approved testosterone products."
In a cautionary note, the FDA also reminded health care professionals "none of the FDA-approved testosterone products are approved for use in men with low testosterone levels who lack an associated medical condition." Whether this advice will reduce the use of testosterone therapy, however, remains to be seen.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.