This one food slashes your dementia risk by a third - if you're a woman

By Brett Arends

If you're female and want to avoid dementia, stock up on this

If you're female and you want to avoid dementia in your golden years, you'd better head down to the store and stock up on some extra-virgin olive oil.

A massive scientific study has found that women who consumed about half a tablespoon of olive oil per day over many years were 33%, or one-third, less likely to die with dementia than women who consumed little olive oil or none at all.

And this was independent of other factors, such as whether they smoked, took regular exercise, or even consumed olive oil as part of a broad "Mediterranean"-style diet.

The study said men also saw a benefit from consuming olive oil, but it was much smaller: Those who consumed an average of seven grams, or about half a tablespoon, a day were 13%, or about one-eighth, less likely to die with dementia than those who didn't take it at all.

Statistically, wrote the authors, the association between olive-oil consumption and a lower risk of dying with dementia "was significant in both sexes but did not remain in men after full adjustment of the model."

Naturally, as with most scientific studies, this can only prove a statistical association between olive-oil consumption and lower dementia risk. It cannot prove that one causes the other.

The study was based on a huge sample of nearly 100,000 middle-aged people who took part in one of two studies: the Nurses Health Study, and the Medical Professionals' Follow-Up Study. Both were in the U.S. and took place over 28 years, from 1990 to 2008.

Analysis was conducted by an international team of researchers, from Harvard University and Brigham and Women's Hospital in Massachusetts, to Copenhagen, Denmark and Hangzou, China. It was published in the Journal of the American Medical Association.

"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," the authors wrote.

Probably the most remarkable thing about the study, other than the differences by sex, is that consumption of olive oil seems to have a health benefit all on its own - even if it isn't part of a broader, so-called Mediterranean diet, meaning lots of fish, fruits, vegetables, nuts and whole grains.

I asked Harvard's Anne-Julie Tessier, the lead author on the study, about this. "Typically, people who use olive oil for cooking or as a dressing have a higher-quality diet, but we found that the association was present regardless of this factor," Tessier told me.

But, she added, this doesn't mean that broader diet is irrelevant. "The lowest risk was observed in people who had both a high intake of olive oil and a high diet quality," Tessier said.

Notably, this was a rare research study that looked at the effects of olive-oil consumption in the U.S., where it isn't the standard salad dressing or cooking oil.

The researchers said most of the previous studies about the benefits of a Mediterranean diet have been conducted in, er, Mediterranean countries. This raises obvious concerns - for instance, how much are the results showing the benefits of the local diet versus the region's famous "Montalbano" lifestyle? And how easy was it to find a good control group of people who don't eat fish, leafy green vegetables, fresh fruit, olive oil, nuts and whole grains?

How do you find a good olive oil? I asked expert Paula Noukas, who has been running Off The Eaten Path, food tours of Boston's historic Italian neighborhood, the North End, for over a decade. She tells me U.S. consumers need to watch out for fake olive oil on the shelves. "Right now EVOO [extra virgin olive oil] is one of the most fraudulent food items because of the increasing demand on supply," she says. For example, "Italy currently exports more oil than it can produce."

Noukas adds: "I tell my guests to make sure their oil is cold pressed, single vineyard (to keep consistent quality), and always, always check for dates of harvest as it only lasts for two years before it goes rancid."

"Also," she adds, "beware of oils that say 'packaged' in Italy. You want to see 'product of Italy' ."

(Oh, and if you fancy buying something off the top shelf, she sent me a helpful list here.)

The latest study adds to the growing pile of evidence in favor of some types of food - and, critically, against others. It is now well established in scientific literature that a Mediterranean diet is associated with lower risks of cognitive impairment or dementia - so much so, actually, that it makes up the major part of the so-called MIND diet that is specifically recommended for brain health.

The MIND diet is based on eating lots of vegetables, berries, nuts, whole grains, fish, legumes, poultry and - of course - olive oil. Among the vegetables, you want to go big on green, leafy ones like spinach and kale, and light on starchy ones like potatoes.

When it comes to olive oil, researchers consistently rate the higher-quality, extra-virgin type, which hasn't been heated or processed. The American Chemical Society says EVOO has specific properties that may account for its effect in helping ward off dementia.

There remains another key issue: When healthy eaters benefit from their diet, how much is it because of the things they eat, and how much is it because of the things they don't eat?

There is, for example, another growing pile of evidence - one linking the "Western" (i.e. American) diet, with its bad fats and processed foods, to dementia and other negative health outcomes. That includes junk foods generally (see here and here and here), processed meats, lots of salt, lots of sugar and refined carbohydrates, and soda (see here and here).

For instance, the Japanese saw a sharp rise in dementia rates as they moved from their own traditional diet to a more Western one.

The MIND diet isn't just about eating healthy foods but also avoiding key unhealthy ones: fried foods, pastries, candy, red meat, cheese, butter and margarine.

And someone who consumes lots of healthy foods is going to have less room for unhealthy ones. So which is more important?

Either way, the "kale effect" is irrational and counterproductive, but I can't be the only one who falls for it: The belief that if I've eaten something healthy like kale, I have somehow earned the right to eat some junk food, as well. The kale counteracts the cheesecake, right?

Do you have questions about retirement, Social Security, where to live or how to afford it at all? We want to hear from you. Join the conversation in our Facebook community: Retire Better with MarketWatch.

-Brett Arends

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05-20-24 1216ET

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