By Gwyneth Dickey, Science News
A combination of diet and lifestyle changes decreases Alzheimer’s-like symptoms in dogs more than either treatment does on its own, a new study shows. The findings show the importance of taking multiple approaches to arrest the disease in humans, the authors say. Their results also provide evidence supporting recent research that suggests plaque deposits in the brain are not the cause of Alzheimer’s.
Alzheimer’s disease usually strikes people over the age of 60 and causes memory loss, shrinking brain tissue and eventually death. People with the disease get plaques in their brains made up of a small protein called amyloid-beta, which clumps together and disrupts brain signals.
Research suggests diet and exercise can improve human brain function and defend against Alzheimer’s, but researchers aren’t sure why. Dogs naturally accumulate the same brain plaque, and though they don’t get Alzheimer’s, they do experience age-related cognitive decline. So scientists can study the animals to learn more about the human form of the disease.
In this study, 24 beagles 8 to 12 years old received one of four treatments over about 2 ½ years. Some dogs were fed a diet enriched with high-antioxidant foods, like spinach, tomatoes, grapes, carrots and citrus fruit. Other dogs were given behavioral enrichment, in which they socialized with other dogs, played with new toys, took long walks and learned new tasks. One group of dogs received both treatments, while the last group received none.
This is the first study to look at antioxidant and behavioral enrichment treatments in dogs that naturally accumulate amyloid-beta plaques, says neuroscientist Viorela Pop, who conducted the research as a graduate student at the University of California, Irvine. The results were published July 21 in the Journal of Neuroscience.
The researchers found that compared with controls, dogs given the combined treatment had the greatest benefit. Those dogs had the biggest improvement in cognition and moderately reduced plaques in their brains. Dogs given just antioxidants fared better than dogs that underwent only enrichment activities. “The combination treatment is a key component of this study,” says Pop, who is now a postdoctoral fellow at Loma Linda University in California. “If we were to try to slow down Alzheimer’s disease in humans, we would want to try a multifactorial treatment.”
Her study also adds to a growing body of research that suggests amyloid-beta plaques, once thought to be the cause of Alzheimer’s, are just a symptom of the disease. Beagles receiving both dietary and behavioral treatments showed major improvements in cognition, but only minor decreases in amyloid-beta plaques in their brains.
The results fit with evidence showing that humans and dogs immunized against amyloid-beta plaques have no clumps but continue to experience cognitive decline, says Alex Roher of the Banner Sun Health Research Institute in Sun City, Ariz. “Patients continue to deteriorate in spite of all treatments, which tells you the plaques are not the ultimate cause of the disease.”
That’s not to say amyloid-beta isn’t important. “It just doesn’t seem to be the main thing responsible for cognitive decline in dogs and Alzheimer’s disease in humans,” Pop says.
Researchers need to conduct more studies before these results can be generalized to humans, says psychologist Catherine Roe of the Washington University School of Medicine in St. Louis. “Going from dogs to people is a big jump,” she says, and researchers need to find links between enriched diet and environment in humans. “So far we haven’t found any association.”
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