Amy Borenstein from the University of South Florida said yesterday that her team had found a 75 per cent reduced risk of the disease among elderly people who drank fruit or vegetable juices at least three times per week compared with those who drank these juices less than once a week.
There was no apparent dementia-related benefit from dietary or supplemental vitamin E, C or beta-carotene intake, she added.
The research was presented at the US-based Alzheimer's Association's first conference on prevention of dementia, running in Washington this week (abstract 05-A-103-ALZ-PC).
There are nearly 18 million people with dementia in the world and the most common cause of this dementia is Alzheimer's disease. By 2025 this figure will rise to 34 million, with 71 per cent of these likely to live in developing countries, making the need for prevention of the uncurable disease crucial.
Ageing populations and increasing overweight are driving incidence of the disease upwards.
The Florida researchers studied more than 1,800 older Japanese American men and women from the Kame Project in Seattle, in which participants were dementia-free at the onset of the study and were followed for up to nine years.
Dietary consumption was determined using a food frequency questionnaire given at the beginning of the study that provided information on intake of fruits, vegetables, tea, wine, and fruit and vegetable juices.
The accumulation of reactive oxygen species in the brain are thought to exhaust antioxidant capacity and lead to the onset or progression of Alzheimer's.
Antioxidant vitamins, particularly vitamin E from dietary fruits and vegetables, has been associated with delayed onset of the disease, although there is little evidence to date that supplements can offer the same benefit.
But animal studies have found that a number of polyphenols from juices have stronger protection for neuronal cells against oxidation than vitamins E and C.
"These findings suggest that something as simple as incorporating more fruit and vegetable juices into our diet may have a significant impact on our brain health," Borenstein said.
The results could lead to a new avenue of inquiry in the prevention of Alzheimer's, the researchers added.
Another poster presentation at the conference found that moderate alcohol consumption could also influence onset of the disease, confirming previous studies showing a benefit from wine in particular.
Author Mark Sager from the University of Wisconsin-Madison medical school said: "These findings contribute to the growing body of evidence that health and lifestyle variables in middle age may be associated with the subsequent risk of developing Alzheimer's in later life."