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Higher olive oil intake was associated with a lower risk of dementia-related mortality, a prospective study of 90,000 healthcare professionals showed.

Eating at least 7 g of olive oil daily -- about a half tablespoon -- was tied to an adjusted 28% lower risk of dementia-related death (pooled hazard ratio [HR] 0.72, 95% CI 0.64-0.81) compared with never or rarely consuming olive oil (P for trend <0.001) over 28 years of follow-up, reported Anne-Julie Tessier, RD, PhD, of the Harvard T.H. Chan School of Public Health in Boston, and co-authors.

The relationship remained significant after adjusting for diet quality, including adherence to a Mediterranean diet, and after accounting for APOE4 gene status, the researchers reported in .

Replacing 5 g (about 1 teaspoon) of margarine and mayonnaise with the equivalent amount of olive oil daily was associated with an 8-14% lower risk of dementia mortality, they noted. Substitutions for other vegetable oils or butter were not significant.

Onset of most dementia types is gradual and progression is slow, making dementia-related mortality difficult to study, Tessier noted. "To our knowledge, this is the first study to examine diet, specifically olive oil, in relation to dementia death," she told MedPage Today.

"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 to be regardless of this factor," Tessier pointed out.

"Current dietary guidelines regarding fats are mainly based on evidence related to cardiovascular health," she added. "Our study contributes to supporting current dietary guidelines recommending choosing vegetable oils such as olive oil, but extends these recommendations to brain-related health."

A number of observational studies have found relationships between brain health and plant-based diets like the Mediterranean or MIND diet that include olive oil, though some research has suggested diet and dementia may not be related.

"As part of the Mediterranean diet, olive oil 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," Tessier and colleagues noted.

The researchers followed 60,582 women from the Nurses' Health Study and 31,801 men from the Health Professionals Follow-up Study from 1990 to 2018. Previous research from these cohorts showed that higher olive oil consumption was tied to lower cardiovascular disease risk and lower mortality.

Mean baseline age was about 54, and participants were free of cardiovascular disease and cancer at baseline. Dementia death was ascertained from death records.

Every 4 years, participants reported olive oil intake on food frequency questionnaires. Scores on the and scale were used to assess overall diet quality.

Mean olive oil intake was 1.3 g/day at baseline and went up over time. During 28 years of follow-up, 4,751 dementia-related deaths occurred.

The association between dementia-related death and olive oil intake was significant for women (adjusted HR 0.67 (95% CI 0.59-0.77), but not men (HR 0.87, 95% CI 0.69-1.09). Joint analyses showed that participants with high olive oil intake had a low risk for dementia-related mortality, regardless of diet quality scores.

In a subset of about 27,000 participants who were genotyped, the overall results were similar after adjusting for the presence of an APOE4 allele (adjusted HR comparing high vs low olive oil intake of 0.66, 95% CI 0.54-0.81, P for trend <0.001).

Olive oil consumption may lower dementia mortality by improving vascular health, Tessier and colleagues suggested, though incident cardiovascular disease, hypercholesterolemia, hypertension, and diabetes were not significant mediators of the relationship between olive oil and dementia-related death in this study.

The study had several limitations, including the possibility of reverse causation, the researchers acknowledged. While results remained consistent after accounting for socioeconomic status and important covariates, residual confounding may have occurred. The study population was predominantly white and results may not apply to others.

In addition, some margarine and mayonnaise contained considerable levels of partially hydrogenated oils during the course of the study, which the FDA warned about in 2013 and subsequently .

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