A provocative new analysis identifies the biggest risk factors for Alzheimer's disease - and concludes that more than half of all cases are potentially preventable through simple lifestyle changes, such as exercising, quitting smoking and losing weight.
It offers no magic bullet against the devastating disease, which kills brain cells and leaves people mute, incontinent and unable to care for themselves.
That's because no one has yet proven that changing these factors actually will reduce risk of the disease, which affects half of all people over age 85 - an estimated 5.2 million Americans. The cause of Alzheimer's remains unclear; like heart disease, it may be caused by a combination of factors.
But the San Francisco VA Medical Center study shows scientists where to start working.
"It's another brick in the wall suggesting that Alzheimer's doesn't have to be a passive thing that we wait to come get us. There are life modifiers that may reduce our risk," said William H. Fisher of the Alzheimer's Association.
It is an issue that has taken on increased urgency with the aging of baby boomers. An estimated 5.3 million people in the United States are diagnosed with the disease, and the number is expected to triple by 2050. Because caregiving is so expensive, experts predict the cost to Medicare and Medicaid will jump from $170 billion in 2009 to $800 billion in 2050 - more than the military budget.
The conclusions based on a statistical analysis of published data were presented Tuesday at the Alzheimer's Association International Conference in Paris and was published in the journal Lancet Neurology.
"It suggests these modifiable risk factors might make a huge difference in those projections," said VA researcher Deborah Barnes in a phone interview from France. "The next step is to do the clinical trials that ask, 'If we change a risk factor, will it reduce rates of dementia?' " There are many reasons to follow practices to improve general health - such as a good diet, exercising and keeping mentally engaged, Fisher noted.
Even if these steps don't guarantee protection against the degenerative brain disease, it might delay its onset.
But Fisher cautioned: "A lot of people are going to do everything right, and they'll still get Alzheimer's disease. We have to be careful not to blame the victim."
The study found that the biggest changeable factor in the United States is physical inactivity - accounting for 21 percent of the risk, followed by depression and smoking. When added together, these risk factors account for about 50 percent of the cases.
Even a 10 percent reduction in the seven risk factors, which also include diabetes, midlife high blood pressure and low education, could prevent 184,000 Alzheimer's cases in the United States and 1.1 million cases worldwide, according to the study.
The findings were based on complex mathematical analysis, not a new study of patients. They assumed a causal relationship between each risk factor and dementia. "What we need to do now is figure out whether that assumption is correct," said Barnes.
The best way to truly prove prevention is to run a controlled experiment that randomly assigns similar people to different lifestyle factors, like diet - then watch, asking: Do they get Alzheimer's, or not? But this takes money - and time.
Just two decades ago, many people thought dementia was a normal part of aging, so not much attention was paid. But in December, Congress voted unanimously to create a national plan to combat Alzheimer's disease with the same energy as the attacks on cancer and AIDS. The national plan will reinforce efforts to detect brain changes that occur years before people develop symptoms.
Last year, in disappointing news, a panel assembled by the National Institutes of Health surveyed the scientific literature, and found no research good enough to prove that Alzheimer's can be fended off.
But Molly Vanden, of Walnut Creek, Calif., already is taking prevention seriously, rather than waiting for a definitive link. She is only 27, but her father, Marc, was diagnosed at 54. He is now 61, and in the middle stages of the disease.
She walks around her neighborhood three times a week, and on weekends goes for longer five-mile hikes with her mother and her dog.
"Anything I can do will help," she said. "I recognize that scientists don't say it's a cure. But I'm hoping it will help. There are things I can do for a healthy lifestyle."
Duke University's Dr. James Burke, a member of the group that conducted the landmark NIH study, said the new analysis "attempts to answer an interesting and important question. What would happen to the prevalence of Alzheimer's disease if we reduced the occurrence of risk factors that may cause Alzheimer's disease?" So far, there is little evidence that these risk factors actually cause Alzheimer's disease, said Burke, who directs Duke's Memory Disorders Clinic. There are many examples in medicine where things that seemed linked weren't, he said.
But the magnitude of the problem makes it important to take steps now, rather than waiting for a definitive answer.
"Reducing smoking, obesity and increasing exercise will have huge benefits in quality of life independent of whether it reduces the number of people with dementia," he added.