High olive oil consumption is associated with a significant decreased risk for dementia-related mortality, regardless of overall diet quality, a new study suggested.
Data from a prospective study of more than 92,000 people showed consuming at least 7 g of olive oil a day — about half a tablespoon — was associated with a 28% lower risk for dementia-related death.
Replacing one teaspoon of margarine and mayonnaise with the equivalent amount of olive oil was associated with an 8%-14% lower risk for dementia-related mortality.
"Opting for olive oil, a natural product, instead of more processed fats such as margarine and mayonnaise, is a safe choice and may reduce risk of fatal dementia," lead investigator Anne-Julie Tessier, RD, PhD, research associate, Department of Nutrition, Harvard T.H. Chan School of Public Health, Boston, told Medscape Medical News.
However, "intervention studies are needed to confirm causal effect and optimal quantity of olive oil intake," she added.
The study was published online on May 6 in JAMA Network Open.
A Spoonful of Olive Oil
A growing body of evidence has shown a link between the Mediterranean diet and preserved cognitive function and lower risk for cardiovascular disease (CVD). But its association with dementia mortality was unknown.
Investigators analyzed data on over 92,000 participants (66% women; mean age, 56 years) in the Nurses' Health Study (NHS) and Health Professionals Follow-Up Study (HPFS) who were free of CVD and cancer at baseline.
Both studies were conducted between 1990 and 2018, with olive oil intake assessed every 4 years using a food frequency questionnaire. Dementia-related mortality was ascertained from death records.
The researchers also evaluated the joint association of diet quality (particularly adherence to the Mediterranean diet and Alternative Healthy Eating Index score) and olive oil consumption with the risk for dementia-related mortality. And they estimated the difference in the risk for dementia-related mortality when other dietary fats were substituted with an equivalent amount of olive oil.
There were 4751 dementia-related deaths during the 28-year follow-up period. People with two copies of the apolipoprotein ε4 (APOE ε4) allele — a known risk factor for Alzheimer's disease — had a fivefold to ninefold greater likelihood of dementia-related death.
Compared with no or rare olive oil intake, consumption of ≥ 7 g of olive oil per day was associated with a 28% lower risk for dementia-related mortality (adjusted hazard ratio [HR], 0.72; P < .001), after adjusting for lifestyle and socioeconomic factors. The finding remained consistent even with further adjustment for the APOE ε4 allele.
Each 5-g increment in olive oil consumption had an inverse association with dementia-related death in women (HR, 0.88; 95% CI, 0.84-0.93) but not in men (HR, 0.96; 95% CI, 0.88-1.04).
No interaction by diet quality scores was found.
No Link With Diet Quality
"Typically, people who use olive oil for cooking or as a dressing have an overall better quality of their diet, but interestingly, we found the association between more olive oil and reduced risk of dementia-related death to be regardless of this factor," Tessier said.
Replacing 5 g per day of margarine and mayonnaise with the equivalent amount of olive oil was associated with an 8%-14% lower risk for dementia mortality. Substitutions for other vegetable oils or butter were not significant.
"Some antioxidant compounds in olive oil can cross the blood-brain barrier, potentially having a direct effect on the brain," Tessier said. "It is also possible that olive oil has an indirect effect on brain health by benefiting cardiovascular health."
The authors noted several study limitations, including the possibility of reverse causation, due to the observational nature of the study.
It is also plausible that higher olive oil intake could be indicative of a healthier diet and higher socioeconomic status, although the results remained consistent after accounting these factors, the authors noted.
The study population included only healthcare professionals and was primarily non-Hispanic White people, which could limit generalizability.
Causality vs Connection
Commenting on the findings for Medscape Medical News, Rebecca M. Edelmayer, PhD, senior director of scientific engagement for the Alzheimer's Association, cautioned that the study was designed to show correlation, not causation.
Other notable limitations include measuring prevalence or incidence of dementia from death records because dementia and Alzheimer's disease are often underreported as a cause of death.
Moreover, people in the highest olive oil consumption group also had better diet quality, higher alcohol intake, were more physically active, and less likely to smoke, Edelmayer said.
"All of these factors may have an impact on risk of cognitive decline and dementia, separately from or in addition to olive oil consumption," said Edelmayer, who was not involved with the study.
She echoed the authors' concerns that the study was conducted in predominantly non-Hispanic White people and noted that the protective benefits of olive oil were no longer statistically significant for men after adjusting for potential confounders.
It "would be wonderful if a particular food could delay or prevent Alzheimer's disease, but we do not have scientific evidence that these claims are true," Edelmayer said. "We need randomized controlled clinical trials to evaluate whether any foods have a scientifically proven beneficial effect."
This study is supported by a research grant from the National Institutes of Health to the senior author. The NHS, NHSII, and HPFS are supported by grants from the National Institutes of Health. Tessier is supported by the Canadian Institutes of Health Research Postdoctoral Fellowship Award. Senior author Guasch-Ferré is supported by a Novo Nordisk Foundation grant. Tessier reported no other relevant financial relationships. The other authors' disclosures are listed on the original paper. Edelmayer reported no relevant financial relationships.
Batya Swift Yasgur, MA, LSW, is a freelance writer with a counseling practice in Teaneck, New Jersey. She is a regular contributor to numerous medical publications, including Medscape Medical News and WebMD, and is the author of several consumer-oriented health books as well as Behind the Burqa: Our Lives in Afghanistan and How We Escaped to Freedom (the memoir of two brave Afghan sisters who told her their story).