This is particularly frustrating because the course of the disease is long and slow (it can be present at subclinical levels for decades), but even if we can know that it is present and advancing, we don't know what to do about it.
The studies included research on nearly everything proposed to prevent the disease: exercise, mental stimulation, healthy diet, social engagement, nutritional supplements, anti-inflammatory drugs or those that lower cholesterol or blood pressure, even the idea that people who marry or stay trim might be saved from dementia. And they included research on traits that might hasten Alzheimer’s onset, like not having much of an education or being a loner. . . .
“Currently,” the panel wrote, “no evidence of even moderate scientific quality exists to support the association of any modifiable factor (such as nutritional supplements, herbal preparations, dietary factors, prescription or nonprescription drugs, social or economic factors, medical conditions, toxins or environmental exposures) with reduced risk of Alzheimer’s disease.”
Lots of studies show that various treatment options could be promising, but “the quality of the evidence was typically low.”
The Alzheimer’s Association tells people to exercise, challenge themselves mentally, remain socially engaged and keep their hearts healthy.
The plus of these recommendations is that they are good for physical health and not harmful, even if they don't prevent Alzheimer's, and hence can't be a bad thing to do in the absence of any more specific evidence of effective treatments.
The best available evidence pertained to things that didn't work:
In the end, it said it was highly confident in the findings for just one thing, the herb ginkgo biloba. But in that case the evidence pointed in only one direction: it did not prevent Alzheimer’s.
Moderate evidence, not totally convincing but not worthless, applied to only four factors studied.
Two were factors that increased risk. They were a particular gene, ApoE4, which, moderate evidence showed, increased risk about threefold, and menopause therapy with a combination of estrogens and progestins, which doubled risk.
The other moderate evidence indicated that certain things that had been hoped to be protective were not. For instance, there was moderate evidence that vitamin E, found in nuts, vegetable oils, green leafy vegetables and fortified cereals, had no effect on risk. There was also moderate evidence that cholinesterase inhibitors, drugs often used to treat Alzheimer’s symptoms, had no effect.
Other than that, evidence was poor.
The study also may provide some guidance as to how health dollars should be spent right now. It doesn't make sense right now to spend money trying to diagnose Alzheimer's for treatment purposes, although it may for other reasons, because a positive diagnosis doesn't tell you to take any action that wouldn't have been good advice anyway. Money is better spent looking for treatments that do work.