Alzheimer’s Risk Curbed by Antioxidants in Fruit and Vegetable Juice
By: Craig Weatherby
Colorful polyphenols in juices outstrip their antioxidant vitamins; Kame Project study in Seattle and Japan separates effects of diet from genetic influences.
Only fear of cancer rivals the anxieties generated by the threat of Alzheimer’s disease, due to its devastating impact on victims and their families.
Consequently, the results of a sizable, 10-year epidemiological study from the Seattle area-part of joint Japanese-American health investigation called the Kame Project-could cause a run on bottled juices and home juicers.
These findings should prompt people to start using more seasonings, too, since the benefits of juices seem to stem from their polyphenol antioxidants, which are even more abundant in culinary herbs and spices like oregano, rosemary, thyme, bay leaf, turmeric, and cayenne pepper.
The new results suggest that drinking fruit and vegetable juices frequently could reduce the risk of Alzheimer’s disease dramatically:
- Participants who drank juices at least three times per week enjoyed an amazing 76 percent drop in the risk of Alzheimer’s disease, compared with those who drank juice less than once a week.
- Participants who drank juices one to two times a week experienced only a 12 percent risk reduction, compared with those who drank juice less than once per week.
The risk reduction was strongest among the study participants who possessed the gene linked to the most common (late-onset) form of Alzheimer’s disease, and in the most sedentary subjects (Dai Q et al 2006).
As the researchers said, “Fruit and vegetable juices may play an important role in delaying the onset of Alzheimer’s disease, particularly among those who are at high risk for the disease. These results may lead to a new avenue of inquiry in the prevention of Alzheimer’s disease.”
And it looks like the constituents most responsible for the preventive effects are the polyphenol-type antioxidants in juices, rather than their antioxidant vitamins, since the researchers’ calculations took into account dietary intake of vitamins E, C and beta-carotene (a vitamin A precursor).
The recent Kame Project results are scientifically plausible for two reasons:
- Polyphenols retard the specific free radicals believed to cause much of the damage in Alzheimer’s patients’ brain cells.
- Polyphenols curb the kind of chronic, low-grade, brain-tissue-damaging inflammation that exacerbates Alzheimer’s disease and generates destructive free radicals.
A literature review published last year by psychiatrists at University of Buffalo School of Medicine reported that the published evidence indicates people can expect at least some degree of preventive benefit from any of eight supplements, beverages, or food factors: green tea, curcumin (the yellow pigment in turmeric), aged garlic extract, melatonin (a bodily antioxidant), resveratrol (found in grapes and red wine), Ginkgo biloba extract, vitamin C, and vitamin E (Frank B, Gupta S 2005).
Kame Project probes effects of nature vs. nurture on dementia risk
These noteworthy results come from the ongoing Kame Project; a collaborative effort of researchers at the University of Washington and the Japanese-American community in Seattle.
By comparing information collected from ethnic Japanese living in different cultures, researchers sought to examine whether differences in diet and lifestyle affect rates of Alzheimer’s disease among genetically Japanese people there and in the US. (This experiment would work with culturally distinct populations of any genetically identifiable racial/ethnic group.)
Between May 1992 and May 1994, more than 1,800 Americans of Japanese descent (54 percent women) enrolled in the project, and another 200 have signed up since. To be eligible they had to be over age 65, of at least 50 percent Japanese heritage, and free of any signs of dementia.
The mental status of study subjects in Seattle, Hawaii, and Japan were all assessed using the same test, administered when they enrolled in the Kame project and every two years subsequently.
Supporting the Kame researchers’ hypothesis that diet and lifestyle influence the risk of AD and other forms of dementia more strongly than genetics, their earliest findings confirmed that rates of Alzheimer’s disease (AD) are higher among Japanese-Americans than among similar people in Japan, and resemble the rates found among white Americans and Europeans (Graves AB et al 1996).
Polyphenols get credit for the positive results
The latest phase of the Kame Project was designed to test whether more frequent consumption of fruit and vegetable juices reduces the risk of Alzheimer’s disease.
The new findings stemmed from responses to diet questionnaires that did not differentiate among various types of juice.
But it appears very likely that the polyphenol-type antioxidants in juices deserve the credit.
The researchers pointed to evidence suggesting that the damage to brain cells seen in Alzheimer’s disease is mediated by a free radical called hydrogen peroxide, which is generated in the beta-amyloid protein plaques characteristic of Alzheimer’s disease. And, as they said, “Many polyphenols, the most abundant dietary antioxidants, possess stronger neuroprotection [powers] against hydrogen peroxide than antioxidant vitamins.”
To confirm this hypothesis, the researchers intend to test the subjects’ blood samples to see if high levels of polyphenols are linked to the same reduced risk of dementia associated with higher juice intake. If so, the juices highest in polyphenols should offer the most protection.
Among the most common juices, the highest levels of polyphenols occur in grape, apple, orange, and cranberry, while acai, pomegranate, berry, and cherry juices are even higher in phenols.
While more research is needed, the results of this sizeable, lengthy study mean that three out of four substantial epidemiological studies conducted to date suggest that fruits and vegetables packed with (often colorful) polyphenols exert strong protective effects:
- A six-year study in 5,395 Dutch people found that high intake of polyphenols or vitamins C and vitamin E was associated with lower risk of Alzheimer’s disease (Engelhart MJ et al 2002).
- A five-year study in 1,367 French people above 65 years of age found that the risk of Alzheimer’s disease fell along with higher consumption of flavonoids, which are one kind of polyphenol (Commenges D et al 2000).
- A 30-year study in 2,459 Japanese-American men native to Hawaii found no association between intakes of beta-carotene, polyphenols, or vitamins E and C and risk of dementia (Laurin D et al 2004).
The protective effects of vitamin E seen in the Dutch data are supported by a French population study (Larrieu S et al 2004), which suggests that it probably plays a supporting role, despite the lack of a protective link in the Kame Project results. This makes sense, since the term “vitamin E” actually describes a group of eight closely related polyphenol compounds called tocopherols and tocotrienols.
Surprisingly, the analysis found no association between higher tea intake and lower risk of dementia. It is hard to explain this negative result, since tea is high in polyphenols, the results of two recent cell studies indicate that tea should be preventive (Rezai-Zadeh K et al 2005, Ayoub S et al 2006), and in Asia, tea possesses an ancient reputation as an anti-aging brain tonic.
The results of the Kame and Dutch studies are certainly plausible given the proven powers of polyphenols against oxygen free radicals in general, and the Alzheimer’s-associated hydrogen peroxide radical in particular.