Between May 2022 and July 2023, researchers from the Harvard T.H.Chan School of Public Health analyzed data from 92,383 women and men who participated in the Nurses’ Health Study (NHS) and Health Professionals Follow-Up Study (HPFS), both conducted from 1990 to 2018. Subjects (65.6% women) had a mean age of 56 years and were cancer- and cardiovascular disease-free at enrollment.
Over the 28-year period, there were 4,751 dementia-related deaths as established by death records. Olive oil intake was assessed every four years using a food frequency questionnaire, and diet quality was based on the Alternative Healthy Eating Index and Mediterranean Diet score.
“In two large U.S. prospective cohorts of men and women, we found that participants who consumed more than 7 g/d of olive oil had 28% lower risk of dying from dementia compared with participants who never or rarely consumed olive oil,” the researchers wrote in the journal Jama Open Network. “This association remained significant after adjustment for diet quality scores including adherence to the Mediterranean diet.”
The study also estimated the difference in risk when other dietary fats like mayonnaise and butter were substituted with an equivalent amount of olive oil.
Olive oil and U.S. dementia mortality rates
Most studies to date have explored the association between olive oil consumption and cognition in Mediterranean countries. Studying populations in the U.S.—where olive oil consumption has traditionally been lower and where age-standardized dementia mortality rates are on the rise—could offer unique insights, according to the Harvard researchers.
They noted that while olive oil, as part of a Mediterranean diet, may exert anti-inflammatory and neuroprotective effects due to its high content of monounsaturated fatty acids and other compounds with antioxidant properties such as vitamin E and polyphenols, more research is needed to explore these associations outside of diet.
The research builds on another recent analysis of the same cohorts, which showed that olive oil consumption was associated with a lower risk of total and cause-specific mortality, including a 29% lower risk for neurodegenerative disease mortality in participants who consumed more than 7 g/d of olive oil compared with little or none. However, the methodology was not designed to examine the association of olive oil and diet quality with dementia-related mortality.
Considering sex differences and hydrogenated oils
In this latest study, the researchers reported that the association was significant in both sexes but did not remain in men after full adjustment of the model.
The multivariable-adjusted hazard ratios for dementia-related death for the highest compared with the lowest olive oil intake (greater that 7 g/d) was 0.67 for women and 0.87 for men. Olive oil intake in 5-gram increments was inversely associated with dementia-related mortality in women but not in men.
“Evidence from trials also showed sex- and/or gender-specific responses to lifestyle interventions for preventing cognitive decline, possibly due to differences in brain structure, hormones (sex) and social factors (gender),” the researchers wrote. “Olive oil intake may be protective of dementia and related mortality, particularly in women.”
In addition, the study found that using olive oil instead of margarine and mayonnaise, but not butter and other vegetable oils, was associated with a lower risk of dementia-related death. The NHS and HPFS, however, were conducted prior to the 2020 U.S. Food and Drug Administration ban on partially hydrogenated oils in foods.
“At the time of the study, margarine and mayonnaise contained considerable levels of hydrogenated trans-fats, which were strongly associated with all-cause mortality, CVD, type 2 diabetes and dementia, which may explain the lower dementia-related death risk observed when replacing it with olive oil,” the researchers wrote.
For future study, they suggested examining the effect of trans-fat-free margarine on cognitive-related effects and carefully considering the association between the sexes and olive oil outcomes.
Source: Jama Open Network
doi: 10.1001/jamanetworkopen.2024.10021
“Consumption of Olive Oil and Diet Quality and Risk of Dementia-Related Death”
Authors: Tessier et al.