Treatment with the hormone testosterone may help prevent Alzheimer's disease, according to a new study on mice published in the Journal of Neuroscience.
Researchers found that low levels of testosterone in mice caused a faster progression of Alzheimer's disease, so the symptoms came on more quickly.
On the flip side, treating the mice by boosting their testosterone levels appeared to slow their memory decline.
These findings raise the possibility that testosterone treatments could help treat or even potentially reduce the risk of Alzheimer's disease in humans, say the researchers from the University of Southern California and the University of California at Irvine.
But that hope might be a little premature.
Moving from animal studies to human research has never been an easy jump.
Despite the fact that humans have about 90 percent of their DNA in common with the mouse, most medical findings in mice do not translate well to humans.
Diseases in Mice, Humans Not the Same
One issue is that mice and humans simply do not suffer from all of the same illnesses, including Alzheimer's disease.
The mice in this study had to be genetically manipulated to show some of the signs of Alzheimer's disease, but didn't have the disease the same way humans do.
Also, the mice were castrated to create the low levels of testosterone. How well this translates to the human situation is not yet clear.
Will the apparent link between low testosterone levels and Alzheimer's disease prove to be one of the few medical findings that are true across species? Maybe, maybe not.
Right now, there is evidence that supports both sides of the argument.
In support of the theory, some research has shown that people with Alzheimer's disease, especially men, tend to have lower levels of testosterone.
For example, one study from the National Institute of Aging followed more than 500 men for 20 years and found that men with low levels of testosterone were at a greater risk for Alzheimer's disease.
Also, small studies have suggested that giving testosterone to older men can improve their thinking.
But the results are far from clear-cut.
A look back at the available evidence from the Institute of Medicine in 2004 found that overall verdict was mixed -- it's not really known whether boosting testosterone benefits the mind.
Also, it is not even clear that low testosterone is definitely linked to memory problems in men.
A large study published this year found no relationship between testosterone levels and risk of Alzheimer's disease in men.
Hope for New Treatments Must Come With Caution
Going forward, there is good reason to be cautious about the study's finding.
Doctors and scientists learned an important lesson from studies on women, hormones and memory.
While early animal research had suggested that taking female hormones like progestin and estrogen could lower a female's risk of dementia and Alzheimer's disease, when doctors actually tested the theory on humans, they found the opposite.
Hormones are linked to an increased risk of dementia in women.
The women taking hormones not only had more memory problems, but they also faced an increased risk of other health hazards such as stroke, blood clots and heart disease -- even though the hormones had helped animals in previous studies.
All of this is good reason for men to take a "wait and see" approach to these new findings.
The researchers in the current animal study agree that more study is needed before it is known whether testosterone treatment could help men fight Alzheimer's disease.