The number of Americans living with Alzheimer’s will triple in the next 40 years, which means that 13.8 million will have the mind-robbing disease by 2050, researchers projected Wednesday.

Previous estimates of what many call “the tsunami of Alzheimer’s” hitting our society as the population ages have come up with similar numbers. This latest projection is notable because it is based on an analysis of more than 10,000 people 65 and older enrolled in the Chicago Health and Aging Project since 1993.

Researchers interview the volunteers every three years to monitor the number who develop Alzheimer’s as they grow older. Census data project that as the baby boom generation ages, the number of Americans ages 65 to 84 will approximately double by 2050. At the same time, the number of those 85 and older will increase almost four-fold to a total of nearly 14 million. The study estimates that 36.6 percent of that population will suffer Alzheimer’s.

Currently an estimated 4.7 million Americans have Alzheimer's, the most common cause of dementia.

“These projections emphasize the need to find either prevention or treatment for Alzheimer’s disease dementia in order to decrease the burden of future disease on individuals, families and the medical care system,” the team at Rush Hospital in Chicago writes in the journal Neurology.

What are the chances of better treatments any time soon? In a few words: not great. Drug companies and academic researchers are carrying out many trials and we can hope for an unexpected great success. But none is apparent.

The FDA has approved five drugs to treat Alzheimer’s. Most physicians say that in a minority of patients they relieve symptoms for a few months. But none stops the inevitable brain destruction.

Still, the drugs generated sales of $2.9 billion in 2011, according to IMS Health, a healthcare technology and information company. The best selling, Aricept from Pfizer, brought in $1.5 billion. Doctors admit that all too often they will give the patient the pills long after it is clear they have no benefit because they want to help, and families expect them to do something even if it affords no improvement.

Early diagnosis will be playing an increasing role in the effort to stop or slow down Alzheimer’s. Recent studies of people who carry gene variants that bring on Alzheimer’s at an early age found that brain changes leading to the disease began as early as 25 years before memory loss or other symptoms set in. Drug trials are now looking at people with the gene variant that predisposes them to Alzheimer’s, trying experimental drugs decades in advance to see if they can slow the process.

As part of the push for early detection, drug company Eli Lilly won approval from the FDA last April for a radioactive tracer that, used with a PET brain scan, measures the build-up of a substance called amyloid plaque that many experts believe is either the cause of Alzheimer’s or a critical marker for its progression.

The company says the product, called Amyvid, can help doctors diagnose Alzheimer’s and rule out other possible, mostly rare, causes of dementia. There is no evidence to date that it can help predict what will happen to people who do not have symptoms. The price of Amyvid, the PET scan and the doctors’ time adds up to $4,000 and federal advisers say Medicare and Medicaid should not pay for it.

So what can a person do to reduce the risk of dementia later in life? Dozens of studies have shown that exercise is very helpful.

One of the strongest pieces of research came out Monday from the Cooper Institute in Dallas. Looking at 25 years worth of records for more than 19,000 people who visited the institute, which specializes in preventive care through fitness, it found that those most fit in their late 40s were 36 percent less likely to develop dementia in their 70s and 80s. Exercise is neither new nor glamorous. But for much disease, including Alzheimer's, it remains a strong defense.

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