How much olive oil do you consume every day? If it’s more than seven grams — about half a tablespoon — you may be significantly less likely to die of dementia than those who eat little to no olive oil at all, a new study finds.
The paper from Harvard researchers followed more than 92,000 people over 28 years — and found a daily dose of the Mediterranean diet staple was associated with a 28 per cent lower risk of dementia-related death, regardless of the quality of the rest of one’s diet.
“I think there’s no such thing as a ‘superfood,’ and that olive oil should not be relied on to prevent dementia and mortality,” Anne-Julie Tessier, the first author on the paper and a postdoctoral fellow at the Harvard T.H. Chan School of Public Health, told the Star. “But certainly, using olive oil and including it as part of a healthy diet is the take-home message.”
Tessier and her team’s peer-reviewed paper was published Monday in journal JAMA Network Open. It is the first to examine the relationship between diet and dementia-related mortality, the authors say.
That said, Tessier warns there’s no evidence of a causal relationship between olive oil and dementia mortality, despite the correlation. That should be the subject of future research, she said.
Olive oil and brain health
The study participants were recruited from two large U.S. prospective cohorts — the Nurses’ Health Study I and the Health Professionals Follow-Up Study. The former included 121,700 U.S. female registered nurses ages 30 to 55; the latter was made up of 51,525 male health professionals ages 40 to 75. The average age was just over 56.
Starting in 1990 and once every four years after, the participants were sent questionnaires on how frequently they consumed certain foods — “including types of fats and oils used for cooking or added to meals in the past 12 months,” the study read.
Their overall diets were also assessed using the Alternative Healthy Eating Index and other dietary scores. The index ranks certain foods and nutrients on whether they’re predictive of chronic disease, essentially measuring the quality of one’s diet.
Over the course of the nearly 30-year-long study — which included more than two million person-years of follow-up time — 4,751 participants died of dementia.
Those who reported olive oil consumption of more than seven grams a day had a significantly reduced risk of dementia-related mortality, even when adjusted for diet quality — meaning unhealthy eaters who consumed plentiful olive oil also saw reduced dementia death rates.
This surprised Tessier, who noted that people who eat more olive oil generally have healthier diets and lifestyles, which may influence results. “It suggests that there may be a direct link between olive oil and brain health, and specifically dementia mortality,” she said.
That being said, those that ate healthy on top of consuming lots of olive oil had the lowest dementia mortality scores of them all, “suggesting that combining higher diet quality with higher olive oil intake may confer enhanced benefit,” the study read.
Meanwhile, participants who substituted just five grams of margarine and mayonnaise per day with olive oil were associated with an eight and 14 per cent reduction in dementia-related death risk, respectively.
How does olive oil affect the brain?
While it’s currently unclear exactly how olive oil affects the brain, studies have long associated its consumption with healthier brain structure, as well as reduced cognitive impairment, risk of Alzheimer’s disease and improved cognitive function.
For her part, Tessier theorized that antioxidants and nutrients in the oil may be directly affecting the brain: “We know that olive oil is rich in healthy fats like mono-unsaturated fatty acids, and it also contains compounds with antioxidant activity ... knowing that some of these compounds can actually cross the blood-brain barrier and reach the brain, we think it might have a potential direct effect on the brain.”
It’s also possible olive oil improves brain function by improving cardiovascular health, she noted. Multiple clinical studies have linked the oil, and particularly extra virgin olive oil, to improved heart and vascular health, as well as reduced inflammation while improving fat metabolism, blood coagulation, oxidative stress and more.
Meanwhile, studies suggest the onset of certain dementias is related to an increased permeability in the blood-brain barrier, possibly leading more toxins to enter the brain. Research shows compounds in olive oil can enhance the functionality of this barrier, potentially explaining the results Tessier and her team documented.
Although the researchers did not record the exact type of olive oil that participants used, Tessier hypothesizes extra-virgin olive oil may be responsible for the impacts seen. “We do think that extra virgin olive oil, that’s richer in polyphenols and other (antioxidant) compounds, might be the reason why we’re seeing this association,” she said.
Study limitations
Tessier warns that despite their striking results, we “cannot establish a causal effect of olive oil because this is not an intervention study.”
It will be the goal of future research to explore how the link between olive oil and brain health functions, and show whether olive oil really is making a direct impact on the brain.
“I’m thinking of designing an actual intervention study to build on these observations,” she said. “So future studies should definitely, for example, provide olive oil to participants to a specific group and assess its impact on cognitive function. Use cognitive testing and see if it has this direct effect.”
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