The study, published in The Lancet, challenged warnings by advocacy groups and some public health officials who forecast a booming increase of baby boomers getting dementia at the same rate of older people today, The New York Times reported.
Study leader Dr. Carol Brayne of the Cambridge Institute of Public Health took advantage of a study involving 7,635 people, ages 65 and older in Britain from 1984-94 who were tested for dementia.
From 2008-11, the researchers assessed a similar randomly selected group of people living in the same areas.
The study found the dementia rate dropped to 6.2 percent from 8.3 percent.
Dr. P. Murali Doraiswamy, an Alzheimer's researcher at Duke University, in the United States, who was not involved with the study called the findings "terrific news," and the common assumption that every successive generation would have the same risk for dementia might not hold true.
In another study, researchers in Denmark found people in their 90s given a standard test of mental ability in 2010 scored substantially better than people who reached their 90s a decade earlier. The study, also published in The Lancet, found nearly one-quarter of those assessed in 2010 scored at the highest level, a rate twice that of those tested in 1998.
However, Maria Carrillo, vice president of medical and scientific relations at the Alzheimer's Association, an advocacy group, said she was not convinced the trends were real or that the United States would have a similar finding. She said the British study had a methodological flaw and that the Danish study might be affected because people in Denmark were generally healthier than those in the United States.
Research has showed dementia is lower among the better educated, as well as among those who control their blood pressure and cholesterol.