It would seem that the old wives' tale "an apple a day keeps the doctor away" has borne fruit again in that a new study suggests that apples, bananas and oranges protect against neurodegenerative diseases, including Alzheimer's.

The study is published in the early online issue of the Journal of Food Science and was conducted by scientists based at Cornell University, Geneva, New York, and colleagues from several universities in Korea, including Gyeongsang National University, Kyung Hee University and Korea University in Seoul.

The most common fruits in both Western and Eastern diets are apples, bananas, and oranges, offering an important source of vitamins, minerals, and fibre, wrote the researchers.

In their study, they exposed PC12 cells, that are very similar to neurons, to phenolics extracted from the three fruits and then put the cells under oxidative stress using H2O2 (hydrogen peroxide).

The PC12 cells were bred using a mix of horse serum and fetal bovine serum. They extracted the fruit phenolics using ultrasound on dried fruit samples in an aqueous methanol solution.

Using a test called MTT reduction, the researchers discovered that the phenolic phytochemicals of the fruits had prevented a significant proportion of cells from succumbing to neurotoxicity from oxidative stress, with varying degrees of success.

MTT reduction measures the cell killing power of a toxin by comparing the amount of surviving mitochondrial enzymes with a control batch of cells not exposed to the toxin.

Of the three fruits, apples appeared to contain the most antioxidants, then bananas and then oranges.

Further tests with lactate dehydrogenase and trypan blue exclusion assays showed that the fruit extracts had reduced neuronal cell membrane damage induced by oxidative stress.

The researchers concluded that:

"These results suggest that fresh apples, banana, and orange in our daily diet along with other fruits may protect neuron cells against oxidative stress-induced neurotoxicity and may play an important role in reducing the risk of neurodegenerative disorders such as Alzheimer's disease."

Alzheimer's disease (AD) is a progressive disease characterized by loss of memory and reduced ability to think and process information. Many research studies have revealed that the brains of people who die of AD show signs of different types of cell damage from oxidative stress.

The authors wrote that fruits and vegetables contain many different antioxidant substances, including vitamin C and polyphenolic phytochemicals. However, the authors had suggested in a previous study that the main antioxidative effect of apples came from the "synergistic activities of phenolics rather than vitamin C".

In their conclusion they also referred to another study that showed apple juice with antioxidants protected brain tissue from oxidative damage and improved cognitive performance in mice that had been genetically induced with AD.

"Effects of Banana, Orange, and Apple on Oxidative Stress-Induced Neurotoxicity in PC12 Cells."
H.J. Heo, S.J. Choi, S.-G. Choi, D.-H. Shin, J.M. Lee, C.Y. Lee.
Journal of Food Science (Online Early Articles).
Published online on 24th January 2008.
doi:10.1111/j.1750-3841.2007.00632.x

Click here for Abstract.

Sources: journal article, Blackwell Publishing press release.

Written by: Catharine Paddock, PhD