June 6, 2007 — -- Low testosterone may lead to a greater risk of death, according to a study presented Tuesday at the annual meeting of the Endocrine Society in Toronto.
Men with low testosterone had a 33 percent greater death risk over their next 18 years of life compared with men who had higher testosterone, according to the study conducted by Dr. Elizabeth Barrett-Connor and colleagues at the University of California at San Diego.
"It's very exciting and potentially a groundbreaking study," said Barrett-Connor. "But it needs to be confirmed."
The study tracked nearly 800 men, 50 to 91 years old, living in California. Their testosterone level was measured at the beginning of the study, and their health was then tracked over the next 20 years.
Testosterone normally declines as men get older. However, a clear definition of "low" testosterone does not yet exist.
"No one knows what low really is," said Dr. Joel Finkelstein, endocrinologist and associate professor at Harvard Medical School. "The study authors defined it at 250 [nanograms per deciliter], which is a definition, but no one has figured out what low is."
Barrett-Connor and her colleagues found that nearly 30 percent of the men they studied met their criterion score of 250 or lower for low testosterone.
They noted that many men with this definition of low testosterone were "healthy men in the community who would not know that they had low testosterone."
Symptoms of low testosterone depend on how low the level is. At the lowest levels, men will have hot flashes, much like those experienced by women during menopause.
"At levels not quite that low, men have decreases in their libido, erectile dysfunction, fatigue and physiological changes many will not immediately recognize," Finkelstein said, adding that these could include loss of strength, decrease in bone density and decreased muscle mass.
However, absent symptoms, there is no reason to get testosterone treatment.
"The indication for testosterone is having a low testosterone level in the presence of symptoms, or physiological consequences such as low bone density," said Finkelstein. "Doctors should not prescribe testosterone because a level is low, or because patients think it will make them live longer."
Barrett-Connor agrees. "Don't take testosterone just because you want to feel like you're 30 again."
And higher levels of testosterone aren't necessarily a good thing, either. The study authors found that for those with medium to high levels of testosterone, there was no added benefit for those with boosted levels.
Some of the side effects of testosterone treatment include sleep apnea, thickened blood and a possible increase in prostate disease for certain patients.
For those who actually need testosterone treatment, though, the hormone can be given in a few different ways, including injection and a in gel absorbed through the skin.
"Testosterone injections are given every one to two weeks and can be administered by the patients themselves," said Dr. Larry Lipshultz, professor of urology at Baylor College of Medicine. "Gels are applied daily."
Men with low testosterone in the study were also more likely to have larger waist girth. These men also appeared to be at higher risk for cardiovascular disease and diabetes.
How testosterone would cause these effects is not yet well understood.
"I don't know that anybody has worked that out at the molecular level yet," said Finkelstein.
Researchers say that caution is warranted, as many other factors still remain unknown.
"Men are going to be very excited by this news," said Barrett-Connor. "But I want people to realize that it's only an epidemiological study. It's very good but not definitive."
Indeed, the study suggested a statistical link — what scientists call an association — between low testosterone and mortality, but it did not prove that one caused the other.
"The next step will be a clinical trial," said Barrett-Connor. She and her colleagues hope to recruit men with low testosterone to participate in a more rigorous study over the next year.
For now, doctors agree that they still would not prescribe testosterone to patients who are otherwise well.
"It certainly will not change my practice," said Finkelstein. "I see it more as a challenge to the scientific community to determine if low testosterone really is a cause of increased death and if so, how that occurs."
Barrett-Connor agrees in proceeding with caution.