The researchers found that higher levels of free testosterone seemed to protect men from Alzheimer's. The team reports that for every 50% increase in free testosterone in the blood, there was a 26% reduction in the risk of developing the disease.
Testosterone usually declines with age, but the team found that men who later developed Alzheimer's had testosterone levels that fell dramatically, in most cases below what is considered normal. By the end of the study, men with Alzheimer's had blood levels of testosterone that were half the levels of the men who remained healthy.
In some cases, the drop in testosterone was detected up to a decade before the men were diagnosed with Alzheimer's.
The researchers found a possible correlation between testosterone drops and the diagnosis of Alzheimer's type dementia. The journalist found that higher testosterone is "protective" (though I bet the researchers hinted strongly that this was so).
It's tiresome and annoying. I put the blame on editors and reviewers of academic journals. They should insist that authors expunge leaps to causation and insert text making it harder for journalists to "sex up" the results.
Alzheimer's appears to be a longterm, maybe lifelong, degenerative process. If there really is an association with a decline in free testosterone I suspect the decline is a manifestation of the same disease process. If high testsosterone reduces the risk of Alzheimer's, I suspect it would be related to some increase in mortality among people with early Alzheimer's -- such as risk taking behavior coupled with declining judgement.