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A Half Teaspoon of Dried Rosemary May Improve Cognitive Function

In Hamlet, Act 4, Scene 5, Ophelia notes that rosemary is for remembrance, an idea that goes back at least a few thousand years to the ancient Greeks, who claimed that rosemary “comforts the brain…sharpens understanding, restores lost memory, awakens the mind…” After all, “plants can be considered as chemical factories that manufacture all sorts of compounds that could have neuroprotective benefits”. So, let’s cut down on processed foods and eat a lot of phytonutrient-rich whole plant foods, including, perhaps, a variety of herbs. Even the smell of certain herbs may affect how our brain works. Unfortunately, as I discuss in my video Benefits of Rosemary for Brain Function, I’ve found much of the aromatherapy literature scientifically unsatisfying. There are studies offering subjective impressions, for example, but while sniffing an herbal sachet is indeed “easy, inexpensive, and safe,” is it effective? The researchers didn’t even compare test scores.

However, even when there was a control group, such as one study where researchers had people perform a battery of tests in a room that smelled like rosemary, lavender, or nothing, and even when the researchers did compare test results, the lavender appeared to slow down the subjects and impair their performance, whereas the rosemary group seemed to do better. Perhaps that was just because of the mood effects, though, as I show at 1:36 in my video. Maybe the rosemary group did better simply because the aroma pepped them up in some way—and not necessarily in a good way, as perhaps the rosemary was somehow overstimulating in some circumstances?

Now, there have been studies that measured people’s brain waves and were able to correlate the EEG findings with the changes in mood and performance, as well as associate them with objective changes in stress hormone levels, as you can see at 2:05 in my video, but is that all simply because pleasant smells improve people’s moods? For instance, if you created a synthetic rosemary fragrance with a bunch of chemicals that had nothing to do with the rosemary plant, would it have the same effect? We didn’t know…until now.

Aromatic herbs do have volatile compounds that theoretically could enter the blood stream by way of the lining of the nose or lungs and then potentially cross into the brain and have direct effects. A 2012 study was the first to put it to the test. Researchers had people do math in a cubicle infused with rosemary aroma. The subjects got that same boost in performance, but for the first time, the researchers showed that their improvement correlated with the amount of a rosemary compound that made it into their bloodstream just from being in the same room. So, not only did this show that it gets absorbed, but that such natural aromatic plant compounds may have a direct effect on changes in brain function.

If that’s what just smelling it can do, what about eating rosemary? We have studies on alertness, cognition, and reduced stress hormone levels inhaling rosemary. “However, there were no clinical studies on cognitive performance following ingestion of rosemary”…until now. Older adults, average age of 75, were given two cups of tomato juice, with either nothing, a half teaspoon of powdered rosemary, which is what one might use in a typical recipe, a full teaspoon, two teaspoons, more than a tablespoon of rosemary powder, or placebo pills to go even further to eliminate any placebo effects.

“Speed of memory is a potentially useful predictor of cognitive function during aging,” and, as you can see at 4:08 in my video, researchers found that the lowest dose had a beneficial effect, accelerating the subjects’ processing speed, but the highest dose impaired their processing speed, perhaps because the half-teaspoon dose improved alertness, while the four-teaspoon dose decreased alertness. So, “rosemary powder at the dose nearest normal culinary consumption demonstrated positive effects on speed of memory…” The implicit take-home message is more isn’t necessarily better. Don’t take high-dose herbal supplements, extracts, or tinctures—just cooking with spices is sufficient. A conclusion, no doubt, pleasing to the spice company that sponsored the study. No side effects were reported, but that doesn’t mean you can eat the whole rosemary bush. In one study, an unlucky guy swallowed a rosemary twig that punctured through the stomach into his liver, causing an abscess from which two cups of pus and a two-inch twig were removed. So, explore herbs and spices in your cooking. Branch out—just leave the branches out.

That twig is like a plant-based equivalent of Migrating Fish Bones!


Interested in more on aromatherapy? See:

For more on spicing up your life, check out:

And, learn more about improving cognition and preventing age-related cognitive decline in:

In health,

Michael Greger, M.D.

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Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.


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