According to a new study, after the age of forty, men with low levels of the male sex hormone testosterone may have a higher risk of death over a four-year period than those with normal levels of the hormone.

The hormone testosterone is linked with virility and energy, and unlike women undergoing menopause, middle-aged men generally do not experience a dramatic decrease in the production of the sex hormones.

Testosterone levels gradually decline as a man ages, decreasing approximately 1.5 percent per year after age 30 and the effects of low testosterone levels include decreased muscle mass and bone density, insulin resistance, decreased sex drive, less energy, irritability and feelings of depression.

For the study Dr. Molly M. Shores and colleagues at the VA Puget Sound Health Care System and University of Washington, Seattle, studied the relationship between hormone levels and death in a total of 858 male veterans older than age 40 years.

All participants had their testosterone levels checked at least twice between 1994 and 1999, with at least one week and no more than two years elapsing between tests. The men were followed for between four and eight years until 2002.

The researchers found that men in the lowest of three categories of testosterone levels were at least 68 percent more likely to die in the following 4-1/2 years than those in the “normal” category.

Of the 858 veterans, 166 had below normal testosterone levels and 35 percent died during the study period compared to a 20 percent death rate for subjects with normal testosterone levels.

Dr. Shores says levels of testosterone drop when serious illness strikes and recovers when the illness passes, or does not if health fails to improve.

Even when the researchers considered other variables that may influence risk of death, such as age, other illnesses and body mass index, the association between low testosterone levels and death persisted.

The study is published in the Archives of Internal Medicine.