If you're an older man, you may want to keep a close eye on the testosterone levels in your body. According to a long-term study, men age 50 and older with low levels of testosterone may have an increased long-term risk of death compared to men with normal testosterone.

"This is the first report linking low levels of testosterone with earlier death in relatively healthy older men,” said Gail Laughlin, study author and assistant professor at the University of California San Diego, in a news release. “These results do not suggest testosterone supplementation for all older men, because levels above average did not make a difference.”

The study involved nearly 800 men, ages 50 to 91, who were living in a Southern California community. All have been participants in the Rancho Bernardo Heart and Chronic Disease Study, which began in the early 1980s. In the beginning, almost one-third of the men had less than optimal blood testosterone levels for men their age.

Laughlin and her colleagues found the group with low testosterone levels had a 33 percent greater risk of death during the next 18 years than the men with higher testosterone. This difference was not explained by smoking, drinking, physical activity or pre-existing diseases.

“We want to emphasize that this is an observational study,” said Laughlin. “We cannot recommend that any man take testosterone based on these results. Only randomized clinical trials can determine whether testosterone supplements are safe and can promote longevity. In the meantime, lifestyle changes to prevent or decrease obesity may also extend longevity."

Approximately 30 percent of men age 60 and older are estimated to have low testosterone. It’s a condition that is often accompanied by symptoms such as low bone and muscle mass, increased fat mass, low energy and impaired physical, sexual, and cognitive functions.

The study is set to appear the Journal of Clinical Endocrinology & Metabolism (JCEM).