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Could munching on fruits and veggies reduce the risk of age-associated dementia (AAD) and improve cognitive performance?
Dementia, a disease associated with progressive cognitive dysfunction and behavioral disturbances, affects roughly 10% of Americans over the age of 65 and about 50% of those ages 85 and older.
Evaluation criteria for AAD and related vascular dementia include impaired intellectual functioning that interferes with normal activities and relationships and diminished ability to solve problems and maintain emotional control. Clearly, these symptoms are not disease-specific. They reflect a constellation of neuropsychiatric pathologies.
Studies suggest dietary and lifestyle modifications may reduce age-related cognitive decline, while other investigations suggest the vegetable-fruit association with cognitive change is less compelling. Before considering the public health implications and reexamining the standard of care, it should be noted that many of these studies assess nonspecific outcomes that do not necessarily reflect clinical assessment of dementia or cognitive performance.
Clinical experience has demonstrated time and again that no stand-alone test is adequate and that convergent validity with another evaluation is essential in drawing any conclusions about the status of neuropsychiatric plasticity, function, and cognition. The challenge of discriminating between “state” and “trait”—i.e., poor attention and concentration vs primary cognitive deficit—demonstrates the importance of achieving convergent validity with psychometric instruments that are more “full-bodied” windows on complex and interrelated domains of cognitive-emotional function.
Methodological caveats such as these notwithstanding, it has been reported that there are 10 dietary and lifestyle interventions that may improve everyday memory and interrupt progressive memory loss (Nelson, 2006). One of these interventions is maintaining a healthy diet that includes fruits and vegetables.
In 2007, the FDA’s Division of Neurology Products encouraged similar interventions (http://www.fda.gov/consumer/features/memoryloss0507.pdf). These interventions included adopting a diet that reduces the risk of vascular diseases, such as heart disease and hypertension; avoiding smoking and alcohol abuse; and maintaining regular exercise.
Both of the preceding publications note that excessive stress may contribute to poor learning (impaired attention and concentration) and impaired memory, and thus, diminished cognitive performance. Recent research conducted at Cornell University describes possible mechanisms by which some fruits may reduce oxidative stress–induced neurotoxicity, using a neuronal cell culture model (Heo et al., 2008). In this research, the PC12 cells from the rat adrenal medulla are a model system for neurosecretion and neuronal differentiation and, in many cases, function as a neurotoxic model for many neuropathies. The researchers noted that extracts of banana, orange, and apple reduced H2O2-induced cytotoxicity, which was ascribed to innate antioxidant phenolics.
Similarly, Shukitt-Hale et al. (2008) reported that a review of neurodegenerative diseases and dietary intervention in rodent models suggests other mechanisms to explain possible beneficial effects—including enhanced cognitive performance—from fruit consumption. Those mechanisms included enhanced neuronal cell signaling, modulation of calcium flux, increased secretion of neuroprotective stress shock proteins, and reduced stress signals in regions of the brain that affect cognitive performance. These intriguing findings support observations by Rogers et al. (2004) that indicate that apple juice concentrate may improve cognitive performance among transgenic mice lacking apolipoprotein E and deprived of folate and vitamin E.
Despite these interesting observations, the critical pathways and traditional absorption and distribution studies have not been conducted. In addition, the usefulness of these observations in public health policy and clinical intervention has not been demonstrated (Rosenberg, 2007). Equally important, it seems that some of the earlier-developed psychometric tools may not be applicable or adequate in the present battery to assess cognitive function following nutritional intervention. Thus, it is incumbent that food scientists, nutritionists, physicians, psychometricians, and psychologists team up to enhance the way we approach the question of nutrition and central nervous system function, including cognitive performance.
References for the above studies are available from the authors.
by Roger Clemens, Dr.P.H.,
Special Projects Advisor, ETHorn, La Mirada, Calif.
by Peter Pressman, M.D.,
Attending Staff, Internal Medicine, Cedars-Sinai Medical Center, Los Angeles, Calif.