Drinking apple juice helps slow the accumulation of the protein fragments that damage the brain in Alzheimer's disease, new research in mice shows.
The protein fragments, known as beta-amyloid, are the building blocks of the plaques that form in the brains of people with Alzheimer's disease.
The findings don't suggest that Alzheimer's disease can be treated by gulping gallons of apple juice, but they do point to the importance of long-term nutrition in preventing aging-related changes like those seen in Alzheimer's disease, Thomas B. Shea of the University of Massachusetts-Lowell, the co-author of the current study, said in an interview with Reuters Health.
He and his colleagues previously demonstrated that giving mice apple juice improved their performance in maze tests, while also preventing the decline in performance that typically accompanies aging; the juice also lowered the animals' beta amyloid production.
In the current study, Shea and his colleague Amy Chan looked at the production of amyloid-beta in normal mice as well as mice bred to lack the gene for apolipoprotein E, which normally helps protect cells from damage by harmful by-products of oxygen metabolism, as process known as oxidative stress. Humans with a variant of the gene, apolipoprotein E4, have an increased risk of Alzheimer's disease.
Shea and Chan fed some of the mice a diet deficient in folic acid and vitamin E, with a slight excess amount of iron, to induce oxidative stress. After a month on the diet, the formation of amyloid beta in the normal mice had roughly doubled, while it had also increased in the apolipoprotein-negative mice. But giving the rodents apple juice prevented levels of the protein fragment from increasing when both types of mice were on the deficient diet.
The researchers had previously shown that mice given apple juice produced less of a protein called presenilin 1, overexpression of which promotes the production of amyloid beta, so the juice could be working through this mechanism, the researchers say.
Oxidative stress plays a key role in the progression of Alzheimer's disease disease, and both genetic and nutritional factors influence the degree of oxidative stress a person experiences, Shea said. Aging increases oxidative stress, he added, while eating a healthy diet with plenty of fruits and vegetables decreases it.
"This is the kind of thing that may make Alzheimer's disease manifest and why it's so tricky to predict whether it's going to happen or not," he said.
The U.S. Apple Association and the Apple Products Research and Education Council fund Shea's apple juice research.
Shea agreed that his findings are an endorsement of the benefits of apple juice, but said that they were not influenced by his funding source, he said.
People who don't like apple juice can try grapefruit or other juices, he noted. "It's what you'll stay with that's important."