The U.S. researchers reported an increase in the number of cases of mild cognitive impairment in the elderly people. This milder mental decline often precedes Alzheimer’s disease and is far more common than earlier thought to be. A Mayo Clinic study of Minnesota residents showed the new cases of older Americans who suffer from mild memory impairment to be a 5 % annual rate; this is not including the half a million Americans who develop Alzheimer’s or other such forms of dementia. Currently there are no treatments to either prevent this mental slide or to reverse it.

Dr. Ronald Petersen, the Mayo scientist who led the study said, "We're seeing that in fact there's a much larger burgeoning problem out there" referring to the people who are at risk of developing dementia.

In the Mayo Clinic Study of Aging, Petersen's team collected data on 1,786 people all cognitively normal between ages 70 to 89 years. After a year, 5.3 % of these had developed mild cognitive impairment, an intermediate stage between normal aging and the beginning of Alzheimer's. The rate of cognitive impairment increased with age, and 3.5 % of those between 70 to 79 developed cognitive impairment while those aged 80 to 89 saw 7.2% developing it. Men were twice as likely to develop mild cognitive impairment as compared to women.

"The rate of new mild cognitive impairment cases, in this group, was considerably higher than anticipated," Dr Petersen said in a news release. "If we extrapolate Alzheimer's incidence rates to MCI, we would expect perhaps 1 to 2 percent per year, but our findings were substantially higher than that." The findings were to be presented on Monday at the International Alzheimer's Disease Conference, in Chicago.

"These results underscore the urgency of developing new and better strategies to create disease-modifying therapies for Alzheimer's," Petersen said. "In addition, for public health purposes, we need to know how many people are cognitively impaired and potentially on the road to Alzheimer's."

Dr. R. Scott Turner, incoming director of the memory disorders program at Georgetown University Medical Center, said, "It's the iceberg under the tip, a prime goal is finding drugs to treat the mild impairment before Alzheimer's develops.”

Greg M. Cole, associate director of the Alzheimer's Disease Research Center at UCLA David Geffen School of Medicine, said that these findings do not augur well for the future. "The risk for Alzheimer's disease and dementia rises exponentially with age, so women have a higher risk of developing dementia and a higher prevalence of Alzheimer's in most studies simply because they tend to live longer," Cole said. "The corollary is that when men live longer from new medical advances that fail to prevent Alzheimer's disease, society as a whole and men in particular will be more at risk for dementia."