In a recent study published in the journal JAMA Network Open, researchers used a large prospective cohort study to investigate the long-term associations between olive oil consumption and dementia mortality risk. Their cohort comprising 92,383 American adults revealed that consuming seven or more grams of olive oil per day was associated with a 28% reduction in dementia-related death compared to participants devoid of olive oil consumption. This study highlights the importance of diet in age-associated cognitive decline and mortality. It suggests that olive oil intake may present an efficient strategy to combat dementia mortality risk among Americans.

Study: Consumption of Olive Oil and Diet Quality and Risk of Dementia-Related Death. Image Credit: ifong / Shutterstock

Food may affect age-associated cognitive decline

Dementia, the umbrella term for a spectrum of diseases affecting one’s ability to recall details and events, process data, or make rational decisions, affects more than 55 million individuals and accounts for more than 33% of all adult deaths globally. While recent advances in medicine have resulted in overall decreases in cardiovascular disease (CVD)-related mortality (strokes and heart disease), trends in dementia prevalence and dementia-associated mortality are alarmingly on the rise, with more than 10 million new cases reported every year.

Extensive research, especially during and immediately following the Coronavirus disease of 2019 (COVID-19) pandemic, has revealed the complex yet undeniable association between good health behaviors (particularly sleep, physical activity, and diet) and chronic disease outcomes, with dietary interventions increasingly being investigated for their beneficial impacts on cardiovascular and age-associated cognitive outcomes. The Mediterranean dietary pattern and its derivatives (e.g., DASH – Dietary Approaches to Stop Hypertension), inspired by the traditional eating habits of citizens of southern Spain, southern Italy, and Crete, has been gaining global traction given its observed anti-inflammatory and neuroprotective benefits.

Olive oil is a fundamental part of the Mediterranean diet and is the primary source of oil and fat in that diet. This oil is known to be rich in monounsaturated fatty acids, vitamin E, and polyphenols, compounds rich in antioxidants, which in turn have been observed to delay dementia onset and reduce Alzheimer’s disease risk. Previous studies on olive oil consumption have revealed that its regular intake, when combined with a healthy diet high in fresh fruits and vegetables and low in processed fats and meats, can effectively improve cognitive outcomes compared to its sporadic or non-intake. Unfortunately, most studies investigating the potential benefits of olive oils have been conducted in Mediterranean countries, with a dearth of evidence from other countries.

About the study

In the present study, researchers investigated the long-term effects of olive oil consumption on a large American cohort to elucidate any potential improvements in dementia-associated mortality outcomes within this population. They further examine how these outcomes change based on diet quality (healthy diet adherence) in tandem with regular olive oil consumption. Their prospective study enrolled participants (N = 92,383) from two preexisting long-term association studies – the Nurses’ Health Study I (NHS; the female participant cohort) and the Health Professionals Follow-Up Study (HPFS; the male participant cohort).

Data for the study was collated over a 33-year-long period between 1990 and 2023 and consisted of biennial assessments of participants’ lifestyle habits and medical histories. NHS and HPFS enrollees with a clinical history of CVD, cancer, implausible daily calorific intakes, or incomplete olive oil consumption data were excluded from the subsequent analysis. The questionnaire (‘Food frequency questionnaire’ [FFQ]) was validated by experts in a smaller test cohort and included more than 130 items. A modified version of the Alternative Mediterranean Index (AMED) score was used for diet quality assessments.

“Participants were asked how frequently they consumed specific foods, including types of fats and oils used for cooking or added to meals in the past 12 months. Total olive oil intake was determined by summing up answers to 3 questions related to olive oil consumption (ie, olive oil used for salad dressings, olive oil added to food or bread, and olive oil used for baking and frying at home).”

Since the apolipoprotein E ε4 (APOE ε4) allele has been almost ubiquitously implicated in increased dementia risk, especially for homozygous carriers, blood (or buccal) samples from a subset of participants (N = 27,296) were collected for APOE genotyping. Deaths and covariates (smoking status, body weight, physical activity levels, menopausal status, medicine, and dietary supplement use) were obtained from the National Death Index and the biennial questionnaires, respectively. Age-stratified Cox proportional hazard models were used for statistical validation to compute the relationship between olive oil intake and dementia-associated mortality.

Study findings and conclusions

Of the 92,383 participants (65.6% women) included in the study, 4,751 dementia-associated deaths were reported over the 33-year follow-up period. Mean olive oil intake across cohorts was found to be 1.3 g//d, with Mediterranean diet adherence estimated at 4.5 and 4.2 points for the NHS and HPFS cohorts, respectively.

“Olive oil intake was inversely associated with dementia-related mortality in age-stratified and multivariable-adjusted models. Compared with participants with the lowest olive oil intake, the pooled HR for dementia-related death among participants with the highest olive oil intake (>7 g/d) was 0.72 (95% CI, 0.64-0.81), after adjusting for sociodemographic and lifestyle factors.”

This study’s highlight is revealing that consistent olive oil intake, when consumed as a part of a healthy balanced diet (herein, the Mediterranean diet), can substantially reduce the risk of age-associated dementia-related mortality in Americans, particularly women. Surprisingly, consuming more than 7.0 g/d of olive oil was found to lower dementia risk even in the absence of the Mediterranean diet, suggesting its independent ability to delay the progression of cognitive decline.