Olive Oil and Dementia: What a Major 2024 Harvard Study Found

Reviewed by the HealthyMag Editorial Team. Last updated: July 2026.

What the 2024 Harvard study actually found

In May 2024, researchers at the Harvard T.H. Chan School of Public Health published one of the largest analyses to date on olive oil and brain health. The study, “Consumption of Olive Oil and Diet Quality and Risk of Dementia-Related Death,” appeared in JAMA Network Open and was led by Anne-Julie Tessier, with senior author Marta Guasch-Ferré.

The team followed 92,383 U.S. adults — 60,582 women from the Nurses’ Health Study and 31,801 men from the Health Professionals Follow-Up Study — for 28 years. Participants reported their eating habits, including how much olive oil they used, every four years. Over that period, the researchers documented 4,751 dementia-related deaths.

The headline result: people who consumed more than about 7 grams of olive oil per day had a 28% lower risk of dementia-related death compared with those who never or only rarely used it. Seven grams is a small amount — roughly half a tablespoon, or what you might use to dress a salad or finish a dish.

The numbers behind the swap

One of the more useful details for everyday cooks came from the study’s substitution analysis. When the researchers statistically modeled swapping just 5 grams a day of certain foods for olive oil, they saw measurable differences. Replacing that amount of mayonnaise with olive oil was associated with a 14% lower risk of dementia-related death (95% confidence interval, 7%–20%), and replacing margarine was linked to an 8% lower risk (95% CI, 4%–12%).

Notably, swapping olive oil for butter or for other vegetable oils did not produce a statistically significant difference in this analysis. In plain terms: the clearest signal was in trading processed spreads like margarine and mayonnaise for olive oil — not necessarily in olive oil being magical on its own.

Why olive oil might help the brain

Researchers have several plausible biological reasons why olive oil could support brain health, though the 2024 study itself did not prove any single mechanism.

First, extra-virgin olive oil is rich in monounsaturated fat, a fat type generally considered heart-friendly. Because the brain depends on a healthy vascular system, anything that supports blood vessels and reduces the burden of stroke and small-vessel damage may plausibly protect cognition over time.

Second, olive oil — especially unrefined, extra-virgin oil — contains polyphenols and other compounds with antioxidant and anti-inflammatory activity. Chronic inflammation and oxidative stress are thought to play a role in the brain changes seen in dementia, so compounds that counter them are of active scientific interest. Study author Anne-Julie Tessier noted that olive oil’s monounsaturated fats and antioxidant compounds may play a protective role for the brain.

These mechanisms are biologically reasonable, but it is worth being clear that a food-frequency study like this one measures what people eat and what happens to their health — it cannot directly show a chemical pathway from the oil to the brain.

The Mediterranean-diet context

The olive oil finding does not stand alone. It fits within a much larger body of research on the Mediterranean diet — an eating pattern high in olive oil, vegetables, fruit, legumes, nuts, whole grains, and fish, and lower in red and processed meat. Years of studies, including large trials such as the Spanish PREDIMED research, have linked this pattern to better cardiovascular outcomes, and a growing set of observational studies has associated it with slower cognitive decline.

That broader context is part of why the olive oil result is taken seriously: it points in the same direction as decades of nutrition and cardiovascular science. At the same time, it is a reminder that olive oil is usually one ingredient inside a whole dietary pattern, and untangling the effect of a single food from everything else a person eats is genuinely difficult.

The honest caveats

This is where careful reading matters. The 2024 study was a prospective observational cohort, not a randomized controlled trial. That means it can show a strong, consistent association, but it cannot prove that olive oil causes lower dementia risk.

The biggest concern with nutrition studies like this is healthy-user bias. People who regularly use olive oil may also exercise more, smoke less, have more income, or make other healthier choices — factors that could independently lower dementia risk. The researchers adjusted for many of these variables and found the association held even after accounting for overall diet quality and genetic risk (including APOE status), which strengthens the case. But no statistical adjustment can rule out every hidden factor.

A few other limits are worth naming. Diet was self-reported, which introduces some error. The participants were mostly white U.S. health professionals, so the findings may not translate perfectly to everyone. And the outcome studied was dementia-related death, not dementia diagnosis or day-to-day cognitive testing — a meaningful but specific endpoint. None of this makes the study weak; it simply means the honest word is “associated with,” not “prevents.”

The practical takeaway

So what should a reasonable person do with this? The safest interpretation is also the simplest. Using olive oil in place of margarine, mayonnaise, butter, or heavily processed spreads is a low-risk change that is consistent with strong cardiovascular evidence and now this dementia-related finding. You do not need large amounts — the study’s benefit appeared at roughly half a tablespoon a day.

What this study does not support is treating olive oil as a supplement, a cure, or a reason to ignore the fundamentals: not smoking, staying physically active, managing blood pressure and blood sugar, sleeping well, and staying socially and mentally engaged. Olive oil is a sensible part of an overall healthy pattern, not a shortcut around it. As always, this article is for general information and is not a substitute for personalized advice from your own doctor.

Frequently Asked Questions

Does olive oil prevent dementia?

No study has proven that. The 2024 JAMA Network Open study found that higher olive oil intake was associated with a 28% lower risk of dementia-related death, but it was observational and cannot establish cause and effect. Olive oil appears to be a healthy choice, but it should be seen as part of a broader lifestyle, not a guaranteed shield against dementia.

How much olive oil should I use?

In the Harvard study, the benefit appeared at more than about 7 grams a day — roughly half a tablespoon. There is no evidence that drinking large quantities does more good, and olive oil is calorie-dense (about 120 calories per tablespoon). A modest amount used in place of less healthy fats is the practical target.

Is extra-virgin olive oil better?

Extra-virgin olive oil is the least processed form and retains more polyphenols and antioxidant compounds than refined “light” olive oils, so it is generally considered the higher-quality choice. The 2024 study looked at total olive oil intake rather than comparing grades directly, so it cannot prove extra-virgin is superior for the brain specifically — but it is a reasonable pick.

Does cooking with olive oil destroy the benefits?

Heat can reduce some of olive oil’s delicate polyphenols, but extra-virgin olive oil is more heat-stable than many people assume and remains suitable for most home cooking, including sautéing and roasting. Using it raw — for dressings or drizzling — preserves the most antioxidant compounds. Everyday cooking does not strip away all of its value.

Butter vs olive oil for the brain?

In the 2024 study’s substitution analysis, swapping margarine and mayonnaise for olive oil was linked to lower dementia-mortality risk, while the butter comparison was not statistically significant. Olive oil is higher in monounsaturated fat and lower in saturated fat than butter, and broader heart-health evidence generally favors olive oil, so it remains the more supported everyday choice.

Does this mean olive oil cures Alzheimer’s?

No. There is no evidence that olive oil cures or reverses Alzheimer’s disease or any other dementia. The study measured an association with lower risk of dementia-related death across a large population over time — it did not test olive oil as a treatment. Anyone concerned about memory or cognition should speak with a physician.

Sources

• Tessier A-J, Cortese M, Yuan C, et al. (senior author Guasch-Ferré M). “Consumption of Olive Oil and Diet Quality and Risk of Dementia-Related Death.” JAMA Network Open. 2024;7(5):e2410021. Published May 6, 2024. Harvard T.H. Chan School of Public Health. Available at: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2818362
• National Institute on Aging (NIH). “Olive oil consumption linked with lower risk of dementia-related death.” Available at: https://www.nia.nih.gov/news/olive-oil-consumption-linked-lower-risk-dementia-related-death
• Harvard T.H. Chan School of Public Health. “Olive oil may reduce risk of death from dementia.” Available at: https://www.hsph.harvard.edu/news/hsph-in-the-news/olive-oil-may-reduce-risk-of-death-from-dementia/