Drink Fruit or Vegetable Juices and Avoid Alzheimer's

Summarized by Robert W. Griffith, MD
November 6, 2006

Summary

A glass of fruit or vegetable juice 3 or more times weekly may fend off Alzheimer's disease, due to their polyphenol content, rather than vitamin antioxidants.

Introduction

Oxidative damage is regarded today as one of the keys to the development of Alzheimer's. That's why many people take antioxidants in the hopes of delaying its onset. One of the targets of oxidative damage is the beta-amyloid peptide, and hydrogen peroxide has been suggested as a possible mediator. This has led to the use of polyphenols, which are described as being the most abundant dietary antioxidants, with stronger neuroprotection against hydrogen peroxide than antioxidant vitamins.

Polyphenols are usually found in the skin and peel of fruits and vegetables; when the produce is mechanically squeezed, the polyphenols pass into the juices. A study done in Japanese Americans, reported in the American Journal of Medicine, has explored the role of drinking juices in the development of Alzheimer's disease over a 9-year period. Here's a summary of the publication.

What was done

The Kame project is part of a larger study of dementia in Japanese people living in Japan and the USA. The Kame cohort consists of participants aged 65 and older living in Washington State, USA. There were 1836 subjects who were free of dementia at enrollment in 1992-1994.

At baseline the Cognitive Abilites Screening Instrument (CASI) was used to assess cognitive function; this was repeated every two years for a total of 4 times. A much broader neuropsychological exam was given to anyone scoring less than 87 out of 100 points on the CASI.

Food-frequency questionnaires were completed by 87% of the participants at baseline; the questions used were appropriate for Asian populations. The usual dietary intake of nutrients, including calories, vitamins C and E, and beta-carotene were calculated for each person.

Other baseline information included smoking, alcohol use, birthplace, education level, physical activity, usual eating preference (Asian or Western), and use of antioxidant vitamin supplements. The sense of smell was ascertained, and the apolipoprotein E (ApoE) gene status was determined.

The participants were classified three times according to their intake of tea, wine, and juices (fruit and vegetable). Each classification used three categories, or 'tertiles": "less than once a week", "once or twice a week", and "at least 3 times a week". These tertiles were used to analyze the risks, or Hazards Ratios, of subjects in each category of developing Alzheimer's disease.

What was found

The average age at enrollment was 72; just over half of the subjects were women. One in five of them possessed an ApoE4 gene, which means they were at increased risk of developing Alzheimer's. Over the follow-up period (average duration 6.3 years) 81 cases of Alzheimer's disease were diagnosed; 63 of these had provided food frequency data at baseline, and were included in the analysis.

Tea drinking, the most popular beverage in these studies, was not associated with Alzheimer's disease risk. Only a few participants drank wine, and although there may have been a trend towards a 'protective' effect of wine on the development of Alzheimer's, this was not statistically significant and so should be ignored. There was no association found for intake of vitamins E, C, or beta-carotene.

After adjusting for factors that might bias the results, such as smoking, education, physical activity, and fat intake, it was found that those reporting drinking fruit or vegetable juice once or twice a week were 16% less likely to develop signs of Alzheimer's; this result was not statistically significant. But those who drank juices three or more times a week were 76% less likely to develop the disease, a statistically significant finding. The 'protective' effect of drinking juices was somewhat greater in those participants who were inactive, had a history of smoking, and who carried an ApoE4 gene.

What these results mean

This study shows that Japanese Americans who drank fruit or vegetable juice 3 or more times a week were 76% less likely to develop the symptoms and signs of Alzheimer's in the next 6 years, compared with those who drank juices less than once a week.

Importantly, there was no such association with the intake of vitamins C, E, or beta-carotene, although these are abundantly present in fruit and vegetable juices; other studies have also failed to find any effect of these substances on the development of Alzheimer's. This suggests that some other constituents were responsible for the benefit shown by the juices. The obvious candidates are polyphenols, such as quercetin, which are able to cross the blood-brain barrier and get to the brain, and which have a nueroprotective effct against hydrogen peroxide. (The major polphenol in tea, catechin, is inneffective against hydrogen peroxide, which may explain why teas had no protective effect in this study.)

The researchers say their results require confirmation in more studies, especially ones designed to detect which polphenol is most effective, and which fruits and vegetables confer the greatest protection. In the meantime, while waiting for results, we suggest you include fruit and vegetable juices in your nutrition plan. They taste good, and carry numerous other health benefits, as well.

Source

• Fruit and vegetable juices and Alzheimer's disease: The Kame project. Q. Dai, AR. Borenstein , Y. Wu ,  et al., Am J Med, 2006, vol. 119, pp. 751--759

Related Links
Fruit and Vegetable Juicing Tips
Wikipedia: Polyphenols
About Nutrition: Quercetin

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