This study examines the association between long-term consumption of olive oil and the risk of dementia-related death, as well as the joint effect of diet quality and substitution for other fats. The research is based on data from two large US prospective cohorts: the Nurses' Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS). Participants were followed for 28 years, with a total of 4751 dementia-related deaths recorded. Olive oil intake was assessed every 4 years using a food frequency questionnaire and categorized into four groups. Diet quality was assessed using the Alternative Healthy Eating Index and Mediterranean Diet score. Key findings include: - Consuming at least 7 grams of olive oil per day was associated with a 28% lower risk of dementia-related death compared to never or rarely consuming olive oil. - The association remained significant after adjusting for diet quality scores, including adherence to the Mediterranean diet. - Replacing 5 grams of margarine or mayonnaise with olive oil was associated with an 8% to 14% lower risk of dementia mortality. - Substitutions of other vegetable oils or butter with olive oil were not statistically significant. The study suggests that higher olive oil intake is associated with a lower risk of dementia-related mortality, regardless of diet quality. These findings support dietary recommendations to include olive oil and other vegetable oils for cognitive health and longevity.This study examines the association between long-term consumption of olive oil and the risk of dementia-related death, as well as the joint effect of diet quality and substitution for other fats. The research is based on data from two large US prospective cohorts: the Nurses' Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS). Participants were followed for 28 years, with a total of 4751 dementia-related deaths recorded. Olive oil intake was assessed every 4 years using a food frequency questionnaire and categorized into four groups. Diet quality was assessed using the Alternative Healthy Eating Index and Mediterranean Diet score. Key findings include: - Consuming at least 7 grams of olive oil per day was associated with a 28% lower risk of dementia-related death compared to never or rarely consuming olive oil. - The association remained significant after adjusting for diet quality scores, including adherence to the Mediterranean diet. - Replacing 5 grams of margarine or mayonnaise with olive oil was associated with an 8% to 14% lower risk of dementia mortality. - Substitutions of other vegetable oils or butter with olive oil were not statistically significant. The study suggests that higher olive oil intake is associated with a lower risk of dementia-related mortality, regardless of diet quality. These findings support dietary recommendations to include olive oil and other vegetable oils for cognitive health and longevity.