The nine-year study involved nearly 2,000 people and was led by Professor Qi Dai of Tennessee's Vanderbilt University.
It showed that the risk of developing Alzheimer's was cut by 76 percent among those who drank fruit or vegetable juice more than three times a week.
Alzheimer’s is a degenerative brain disease that affects a person's memory, thinking and mood.
Among those who drank juice once a week, the risk was reduced by 16 percent.
The study focused on 1,836 dementia-free people in Seattle, Washington beginning in 1991.
They were tracked by questionnaires on their lifestyle and eating habits, as well as by cognitive function tests that were conducted every two years.
The scientific community has long thought that antioxidant vitamins like vitamins C and E or carotene had protective benefits against Alzheimer's.
The study has confirmed their belief that "there was maybe something else," Professor Dai said, pointing to polyphenols, natural antioxidants found in juice, tea and wine.
"Animal studies and cell culture studies confirmed that some polyphenols from juices showed a stronger neuroprotective effect than antioxidant vitamins. So we are now looking at polyphenols," Professor Dai said.
The study did not indicate whether some types of juice were more beneficial than others.
The study was part of a larger research project examining Alzheimer's disease in Japan, Hawaii and Seattle. The illness affects more than 10 million people worldwide.