MONDAY, May 9 (HealthDay News) -- Numerous studies have attempted to link specific behaviors and health conditions to the onset of Alzheimer's disease, but scientists still can't say for sure that anything you do or don't do will prevent the brain disorder, according to a new U.S. review of recent research.

The U.S. National Institutes of Health convened a conference last spring to analyze 18 studies of potential risk factors, such as poor eating habits, chronic illness, smoking or little exercise, and development of Alzheimer's disease.

"Although we are not dismissing the potential or important role that these major risk factors might play in the development of Alzheimer's disease, at this time, with what we have currently, we cannot confirm any risk associations," said study lead author Dr. Martha L. Daviglus, a professor of preventive medicine and medicine at the Northwestern University Feinberg School of Medicine in Chicago.

"So we need to conduct more research, if we want to have the evidence in hand," she added.

The study, which summarizes the NIH conference results, is published in the May 9 online edition and September print issue of the Archives of Neurology.

For now, older age is the leading known risk factor for Alzheimer's disease, the study noted. A gene variation is also tied to increased risk, it said.

An estimated 5.3 million Americans struggle with Alzheimer's, a figure projected to grow as the country's Baby Boomer population ages, the authors said. The disease is responsible for between 60 and 80 percent of dementia cases.

"What we're talking about here is something that is going to affect so many Americans in the years to come," said one expert, Catherine Roe, an instructor in neurology at Washington University School of Medicine in St. Louis. "In fact, there's going to be an explosion in the next 50 years, because everyone is living longer in general," she said.

The studies included in the NIH research review were conducted between 1984 and 2009 in English. Participants were at least 50 years old and living in developed countries.

Some of the studies looked into dietary influences, such as folic acid intake, Mediterranean diet and nutritional supplements. Others looked for a link between health problems, such as diabetes or high cholesterol, and Alzheimer's. Still others explored levels of physical activity or alcohol consumption and risk of Alzheimer's disease.

The NIH team found that, as a whole, the studies were "compromised by methodological limitations" that undercut the ability to draw a firm association between any particular behavioral habit and/or health condition and Alzheimer's.

The authors noted that such limitations resulted from the use of poor diagnostic criteria, poor knowledge of the inner workings of Alzheimer's disease itself, and/or the unreliability of patient-reported physical and mental health status.

Yet despite determining that the current quality of evidence is "inadequate" to draw causal linkages, Daviglus and her colleagues stressed that the general public should still focus on lifestyles that avoid behaviors already linked to other chronic diseases.

"People should follow a healthy lifestyle, which includes exercising, blood pressure control, not smoking, not becoming overweight, and trying to sleep properly," Daviglus said.

"And, of course, our recommendation is that it is very important that we make sure that, in the future, more well-constructed, well thought-out studies be conducted so that we can get better quality results that can confirm associations, when they exist, between risk factors that a large proportion of the population have and the onset of Alzheimer's," she added.

Roe agreed that "more quality research is needed," but added that, "I don't think it's a worse situation than in any other field of research. This is difficult and challenging work. And it costs a lot of money at a time when there's a funding crisis in science."

Still, a sense of urgency should prevail, Roe said. "Today the Baby Boomers are starting to hit the age where Alzheimer's comes into play," she noted. "And it's going to take a huge human toll and economic toll, if we don't find a way to treat it or slow it down. So it's very important that we do more and do it better."

More information

To learn more about Alzheimer's disease, visit the U.S. National Library of Medicine.