A new study by UCSF researchers finds that older men
with higher testosterone levels performed better on tests of cognition, which suggests
that older men who are prescribed testosterone supplements may reduce their risk of
cognitive decline, a precursor state to Alzheimer's disease.
Men's bodies tend to produce less testosterone as they age, and some doctors have begun
prescribing supplements of the hormone to increase libido and treat other age-related
problems in men.
"The men in the study with higher levels of bioavailable testosterone, the
testosterone that can reach the brain, did significantly better on these cognitive tests
than men with lower levels," said lead author Kristine Yaffe, UCSF assistant
professor of psychiatry, neurology and epidemiology and biostatistics, and chief of
geriatric psychiatry at San Francisco Veterans Affairs Medical Center.
However, Yaffe does not recommend that men begin taking testosterone to improve
cognition. "Our study only looked at natural testosterone levels and so it doesn't
prove that testosterone supplements can prevent cognitive decline. We will need results of
large randomized clinical trials in older men before we can confidently say that
testosterone supplements are beneficial and safe," she said.
Taking testosterone, or over-the-counter supplements that boost levels of the hormone,
can have side effects including increased risk of prostate cancer, increased cholesterol
levels, acne and male pattern baldness, Yaffe said.
Although some previous studies have suggested that testosterone might benefit the
brain, most of these studies were of younger men, she said.
The study, which was published in the April issue of the Journal of the American
Geriatrics Society, looked at 300 older men enrolled in a larger study of risk factors for
osteoporosis in men that included cognitive testing.
The cognitive tests measured concentration, memory, attention, language, and other
cognitive skills. When scores on these tests decline significantly, or are well below
average, this serves as a warning of a high risk of Alzheimer's disease, Yaffe said.
In addition to testosterone, the researchers measured estrogen and sex hormone-binding
globulin, a protein that binds these two hormones. Although testosterone was linked to
better scores on the tests, estrogen had essentially no effect on performance, Yaffe said.
Previous studies of women have shown that higher estrogen levels can reduce their risk of
Other research has shown that men have higher levels of both estrogen and testosterone
than women, and that women have a 30 percent greater risk of developing Alzheimer's
Disease, Yaffe said. Some researchers hypothesize that women's increased Alzheimer's risk
is related to lower hormone levels. This study doesn't explain how testosterone acts on
the brain, Yaffe said, but other studies of mice have shown that the parts of the brain
that handle learning and memory tasks are replete with receptors for testosterone.
In comparing scores, the researchers focused on bioavailable testosterone, which is not
bound to the proteins, Yaffe said, because when the hormone is bound to protein it has
essentially no effect on the brain.
Co-investigators on the study included: Joseph Zmuda, assistant professor of
epidemiology, and Jane Cauley, associate professor of epidemiology, both at the University
of Pittsburgh; and Lilly Lui, from UCSF Prevention Sciences Group.
Source: Kevin Boyd