Two new animal studies by researchers at the University of South Florida Center for Aging and Brain Repair and James A. Haley Veterans Hospital bolster a growing body of evidence that certain fruits and vegetables may protect the brain against the ravages of age. The complementary research papers appear in today's issue of the Journal of Neuroscience.
"If these pre-clinical findings translate to humans, it suggests that eating a diet high in antioxidant-rich fruits and vegetables may help reverse declines in learning and memory as you get older," Paula Bickford, PhD, lead author of both studies and a professor at the USF Center for Aging and Brain Repair.
In the first study, co-authored by USF's M. Claire Cartford, PhD, older rats fed a diet rich in spinach for six weeks showed a reversal in the normal loss of learning that occurs with age. The rats that ate rat chow containing 2 percent freeze-dried spinach learned to associate the sound of a bell tone with a subsequent puff of air faster than those fed regular rat chow, the study found.
The test measured how quickly the rats learned to blink, after hearing the tone, in anticipation of the oncoming puff of air -- a conditioned response shown to slow with age in rodents and humans.
Spinach is rich in antioxidants, which scientists say can counteract free radicals generated in the body during normal metabolism and exposure to environmental insults such as pollution, ultraviolet light and radiation. An excess of free radicals can damage cellular lipids, protein and DNA. Studies suggest that a lifelong accumulation of free radicals can slow mental processes in old age and may be a factor in Alzheimer's and Parkinson's diseases, Dr. Bickford said.
The second study, co-authored by Carmelina Gemma, PhD, of USF and James A. Haley VA Hospital, found that the benefit of a diet high in fruits and vegetables depends on the levels of antioxidant nutrients in the fruits and vegetables. Furthermore, the researchers suggest, the protective effect of antioxidants may be linked to their ability to reverse age-related accumulations of potentially harmful inflammatory substances in the brain.
The USF researchers compared three groups of older rats. One group ate a diet supplemented by spirulina, a blue-green algae high in antioxidant activity. The second group was fed a daily ration of apple, a food moderate in antioxidant activity, with their rat chow. The third group ate a cucumber-enriched diet, low in antioxidant activity.
Aged rats fed either spirulina-or apple-enriched diets for two weeks demonstrated improved neuron function, a suppression of inflammatory substances in the brain, and a decrease in malondialdehyde (MDA), a marker for oxidative damage. In fact, spirulina reversed the impairment in adrenergic neural function normally associated with aging. There was no improvement in rats fed a diet supplemented with cucumber.
"Not all foods are created equal," Dr. Bickford said. "Cucumbers taste good and have lots of fiber. But unlike spirulina and apples, they are not rich in phytochemicals that have antioxidant or anti-inflammatory effects in the brain."
The research has hopeful implications for the prevention of neurodegenerative disorders in an increasingly aging population, but still must be tested in humans, Dr. Bickford said.
Until then, the USF neuroscientist recommends that daily diets include a variety of richly colored fruits and vegetables -- the most colorful ones tend to pack the greatest antioxidant punch. She favors spinach salads for lunch and routinely snacks on blueberries and strawberries.
"Studies like these are lending scientific credibility to what nutritionists, and our mothers, have been telling us for years," Dr. Bickford said. "Eat your fruits and vegetables. They're good for you!"
Researchers at the University of Colorado Health Sciences Center and Denver Veterans Affairs Medical Center contributed to the study on diets enriched with spirulina, apples and cucumbers.