Olive oil could help reduce risk of dying from dementia, Harvard study says - UPI.com

1 of 2 | Consuming olive oil could help reduce the risk of dying from dementia, regardless of overall diet quality, a new Harvard study of U.S. adults suggests. Photo by Steve Buissinne/Pixabay

NEW YORK, May 6 (UPI) -- Consuming olive oil could help reduce the risk of dying from dementia, regardless of overall diet quality, a new study of U.S. adults suggests.

Results of the study, conducted at the Harvard T.H. Chan School of Public Health in Boston, were published Monday in JAMA Network Open.

Most earlier studies on olive oil intake and cognition occurred in Mediterranean countries, so measuring its effects on the U.S. population, where consumption tends to be lower, could shed unique light on this healthy source of fat, the researchers wrote.

"Olive oil is rich in monounsaturated fats and contains compounds with antioxidant activity that may play a protective role for the brain," the study's lead author, Anne-Julie Tessier, a registered dietitian and research associate at the Harvard T.H. Chan School of Public Health, told UPI via email.

In a Mediterranean diet, olive oil "appears to have a beneficial effect against cognitive decline," said Tessier, who has a doctorate in human nutrition. "Higher olive oil intake was previously associated with a lower risk of cardiovascular disease and mortality, but its association with dementia mortality was unknown."

For most forms of dementia, onset is gradual and progression is slow. As a result, Tessier noted, researchers find it challenging to study dementia-related death because it takes a long time for these cases to emerge.

However, in this investigation, researchers were able to assess 92,383 participants with an average age of 56.4, including 60,582 women (65.6%).

They extracted data spanning from 1990 to 2018 in the Nurses' Health Study and Health Professionals Follow-Up Study. The population included women and men without cardiovascular disease and cancer at the baseline.

Researchers evaluated olive oil intake every four years with a food frequency questionnaire. They categorized consumption as never or less than once per month; greater than 0 to less than or equal to 4.5 grams per day; greater than 4.5 grams per day to less than or equal to 7 grams per day; and greater than 7 grams per day.

During a 28-year follow-up, 4,751 dementia-related deaths occurred. People who inherited from both parents the apolipoprotein ε4 (APOE ε4) allele -- a risk gene tied to late-onset Alzheimer's disease -- were five to nine times more likely to die from dementia, the study showed.

Meanwhile, adults who consumed at least 7 grams of olive oil per day, or half of one tablespoon, had a 28% lower risk of dementia-related death compared with those who never or rarely ingested olive oil. The results held steady after the researchers adjusted for APOE ε4.

Researchers also found that substituting 5 grams of margarine and mayonnaise per day, or one teaspoon, with the equivalent quantity of olive oil had an 8% to 14% lower risk of dying from dementia.

"To our knowledge, this is the first study to examine diet, specifically olive oil, in relation to dementia mortality," Tessier said. The researchers "designed this analysis to be particularly robust," drawing on a significant sample size with extensive follow-up, which solidified confidence in their results.

In addition, "by repeatedly measuring diet and accounting for sociodemographic and lifestyle factors in our statistical models, we were able to isolate as much as possible the effect that olive oil consumption may have on dementia mortality," she said.

"For example, people who use olive oil for cooking or as a dressing typically have an overall better quality of their diet, but interestingly, we found the association to be regardless of this factor," Tessier added. "This suggests a specific benefit associated with olive oil consumption itself."

Lifestyle choices, including dietary decisions that people make in midlife, affect brain health, said Dr. Amalia Peterson, an assistant professor of neurology at Vanderbilt University Medical Center in Nashville. She was not involved in the new research.

"The large sample and long period of follow-up are strengths of this study," Peterson said.

Dr. Kostas Lyketsos, a professor of psychiatry and director of the Johns Hopkins Memory and Alzheimer's Treatment Center in Baltimore, said the research is reliable, but cautioned this is just one study.

"We like to have confirmation," Lyketsos said. "I don't believe we have that at this point."

The study only examined people's health and death records, as well as diet and food frequency questionnaires, in attempting to identify possible links between olive oil intake and risk of dementia-related death, Rebecca Edelmayer, senior director of scientific engagement at the Alzheimer's Association in Chicago, told UPI via email.

"What it's not is an intervention study where some people ate olive oil and some didn't -- the 'gold standard" for the way a treatment clinical trial is conducted," Edelmeyer said. "That means this study can show an association or connection between two things, but can't prove cause and effect."

The study also did not distinguish between intake of refined or unrefined, or virgin, olive oil, even though it's known that polyphenols -- bioactive substances believed to affect cognition -- vary among these different types, said Caroline West Passerrello, community coordinator and instructor in the dietitian nutritionist program at the University of Pittsburgh School of Health and Rehabilitation Sciences.

To improve total wellness and target disease prevention, Passerrello recommends limiting saturated fats, which are solid at room temperature, and more frequently incorporating olive oil and other unsaturated fats, which are liquid at room temperature, into one's diet.

"I will also consider this as one more tool in a giant toolbox for the pursuit of overall health, wellness and longevity," Passerrello, a spokeswoman for the American Academy of Nutrition and Dietetics, said of the new research.

The study "is good news for those of us who enjoy olive oil," said Thomas Laudate, a clinical neuropsychologist at Tufts Medical Center in Boston.

Moreover, "to maximize cognitive health and reduce risk of dementia," Laudate said, "the current best scientifically based evidence suggests we should also be eating a comprehensively healthy diet, such as MIND, Mediterranean or DASH, engaging in regular exercise as recommended by one's doctor, and staying socially and cognitively engaged."