Here’s a question for you. What’s the best way to live a longer, healthier life? Diet? Exercise? Both—eating healthy while doing jumping jacks? Welcome to the Nutrition Facts Podcast. I’m your host Dr. Michael Greger and I’m here to help you answer that question. We have tremendous power over our health destiny and longevity. The vast majority of premature death and disability is preventable with a healthy enough diet and lifestyle. And, I’m here to bring you the latest peer-reviewed research to give you the tools to put it into practice.
On today’s show we look to improve our most valuable assets—our brains. What can we do to maintain optimal brain health especially as we age.
In our first story we compare avocados, greens, and lutein and zeaxanthin supplements for improving cognitive function.
Dark green leafy vegetables are packed with a brain antioxidant called lutein. And so, increasing our greens intake could be an “important public health strategy for reducing the risk of visual or cognitive impairment.” Lutein is the dominant dietary pigment in the retina of the eye as well as the brain; and so, “not surprising that macular pigment,” the concentration of lutein in the center of the eye called the macula, “was found to be significantly correlated with levels in” the brain, which may explain the link between how much of these greens nutrients you can see in the back of the eye and cognitive function. The neuroprotection is assumed to be because lutein is such a powerful antioxidant, but it also has anti-inflammatory properties.
“This relationship between lutein and another greens nutrient called zeaxanthin and visual and cognitive health throughout the lifespan is compelling.” But that was based on observational studies, where you observe that higher lutein levels and brain function seem to go together, but you don’t know if it’s cause and effect until…you put it to the test. “Could lutein and zeaxanthin be supplemented as part of a lifestyle intervention to both improve [brain] function and reduce the probability of slipping into dementia?” The reason everyone is so excited about the possibility is because of the hopeful data from eye health studies that have convinced many ophthalmologists to start recommending people start increasing their lutein and zeaxanthin intake to prevent and treat macular degeneration, a leading cause of age-related vision loss. You don’t have to take pills, though. Adding as little as 60 grams of spinach a day for a month—that’s like one-fifth of a ten-ounce package of frozen spinach—can significantly boost macular pigment in most people.
And it not just good for treating diseased eyes. A randomized, placebo-controlled study found that these greens goodies can improve visual processing speed in young healthy people—that’s like when you’re trying to hit a fastball and your body has to start reacting before you even consciously register it, with real-world benefits outside the major leagues, improving, for example, visual performance during driving. Okay, but what about cognition?
A randomized, double-blind, placebo-controlled trial of adults, average age 73, given the equivalent of about a half-cup a day’s worth of cooked kale, or a full cup of cooked spinach, and got significant improvements in cognitive function compared to those randomized to the placebo.
It may even work in young adults too; average age 21. Daily supplementation with that same amount of lutein and zeaxanthin not only increased their macular pigment, but resulted in significant improvements in brain function—spatial memory, reasoning ability, and complex attention.
Have they ever tried putting whole foods to the test? Hard to get Americans to eat greens every day, but not so hard to get them to eat guacamole. “This study tested the effects of the intake of avocado on cognition. …a six-month, randomized, controlled trial.” What was the control? One avocado a day, or a potato, or a cup of chickpeas, and…those in the avocado group had a significant improvement cognitive function. But, to the Avocado Board’s chagrin…so did the tater and chickpea group. That’s the problem with having healthy placebos; maybe they should have used iceberg lettuce or something.
What about the impact on cognition of those who really need it: Alzheimer’s disease patients? Their vision got better; that’s good, but no significant changes in cognitive function. Now it’s possible that eating whole foods, like dark green leafies, might have worked better than just the pigments in pill form.
Yes, “oxidation and inflammation appear to be key” to both Alzheimer’s and macular degeneration, but “neither disease seems particularly amenable to late-stage treatments.” That’s why prevention is the key. Reducing oxidation and inflammation in the earliest stages may be “our most promising approach.”
In our next story, we discover how a half-teaspoon of dried rosemary can improve cognitive function.
In Hamlet, act IV, scene V, 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, and awakens the mind.” After all, plants can be considered little “chemical factories” that manufacture all sorts of compounds that could have “neuroprotective benefits.”
So, let’s cut down on processed foods; eat lots 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, I’ve found much of the aromatherapy literature scientifically unsatisfying. Like, there will be studies like this, offering subjective impressions. And so, fine, sure, sniffing an herbal sachet is indeed “easy, inexpensive, and safe,” but is it effective? They didn’t compare test scores, or anything.
Even when there is a control group, where researchers had people do a battery of tests in a room that smelled like rosemary, lavender, or nothing, and even when they did compare test results, the lavender appeared to slow them down, impair their performance, whereas the rosemary group seemed to do better. But, maybe that’s just because of the mood effects. Maybe the rosemary group did better just because the aroma kind of pepped them up? And, not necessarily in a good way, maybe kind of 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, along with objective changes in stress hormone levels. But is this all just because pleasant smells improve people’s moods? Like, if you created some synthetic rosemary fragrance with a bunch of chemicals that had nothing to do with the rosemary plant, would it still have the same effect? We didn’t know, until now.
Aromatic herbs do have volatile compounds that theoretically could enter the bloodstream by way of the lining of the nose or lungs, and then potentially cross into the brain, and have direct effects. But, this was the first study to put it to the test. They had people do math in a cubicle infused with rosemary aroma. And so, yes, they got that same boost in performance, but for the first time, showed that how much better they did correlated with the amount of a rosemary compound that made it into their bloodstream, just from being in the room. And so, not only did this show that it gets absorbed, but that such natural aromatic plant compounds may be playing a direct effect on changes in brain function.
If that’s just what smelling it can do, what about eating rosemary? We have the studies on alertness and 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 75, were given two cups of tomato juice, with either nothing, or a half-teaspoon of powdered rosemary, which is what one might use in a typical recipe, or a full teaspoon, two teaspoons, or over a tablespoon of rosemary powder. And, they even gave them some placebo pills to go with it, to even further eliminate any placebo effects.
“Speed of memory is a potentially useful predictor of cognitive function during aging.” And, what they found is that the lowest dose had a beneficial effect, accelerating their processing speed. But, the highest dose impaired their processing speed, maybe because the half-teaspoon dose improved alertness, while the four-teaspoon dose “decreased alertness.” So, “rosemary powder at the dose nearest to normal culinary consumption demonstrated positive effects on speed of memory”—the implicit take-home message being more isn’t necessarily better. Don’t take high-dose herbal supplements, extracts, 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 bush. So, explore herbs and spices in your cooking. Branch out; just leave the branches out.
Finally, we look at how the consumption of blueberries and strawberries is associated with delayed cognitive aging by as much as 2.5 years—because of brain-localizing anthocyanin phytonutrients. Here’s the story.
“A plant-based diet is thought to have played a significant role in human evolution and the consumption of whole plant foods…and even just extracts has repeatedly been associated with… decreased risk of aging-related diseases.” And, by healthy aging, I’m not talking preventing wrinkles. What about protecting our brain?
“Two of the most dreaded consequences of dementia with aging are problems moving around and difficulty remembering things. Dementia robs older adults of their independence, control, and identity.” What can we do about it?
Well, fruits and vegetables help reduce the risk of other chronic diseases. Might they work for brain diseases, as well? “There has been a proliferation of recent interest in plant polyphenols as agents in the treatment of dementia.” There are 4,000 different kinds found “ubiquitously in foods of plant origin.” But, berries are packed with them, possessing “powerful antioxidant and anti-inflammatory properties.” And, there’s a subset of a subset called anthocyanidins—natural blue-purple pigments “uniquely and specifically capable of both crossing the blood-brain barrier and localizing inside brain regions involved in learning and memory…” And, that’s where we need it.
The brain takes up less than like 2% of the body weight, but may burn up to 50% of the body’s fuel, creating a potential firestorm of free radicals. So, maybe these brain-seeking phytonutrients in berries could fight oxidation, inflammation, and increase blood flow. So, this raised a “thought-provoking idea.” Maybe a “nutritional intervention with blueberries may be [beneficial] in forestalling or even reversing the neurological changes associated with aging.”
So, did researchers give blueberries to people, and see what happened? No. they gave blueberries to rats. It would be a decade before the first human trial. But, it worked! Blueberry supplementation improves memory in older adults, suggesting that “consistent supplementation with blueberries may offer an approach to forestall or mitigate” brain degeneration with age.
What other blue/purple foods can we try? Concord grape juice had a similar benefit, improving verbal learning—suggesting that “supplementation with purple grape juice may enhance cognitive function in older adults with early memory decline.” Why use juice, and not whole Concord grapes? Because then, you couldn’t design a placebo that looked and tasted exactly the same, to rule out the very real and powerful placebo effect. And, also, because it was funded by the Welch’s grape juice company.
This effect was confirmed, though, in a follow-up study, showing for the first time an increase in neural activation in parts of our brain associated with memory using functional MRI scans. But, this brain scan study was tiny—just four people in each group. And, same problem with the blueberry study; it just had nine people in it.
Why haven’t large population-based studies been done? Because we haven’t had good databases on where these phytonutrients are found. We know how much vitamin C is in a blueberry, but not how much anthocyanidin—until now. The Harvard Nurses’ Health Study followed the cognitive function of more than 16,000 women for years, and found that “higher, long-term consumption of berries was associated with significantly slower rates of cognitive decline in this cohort of older women, even after careful consideration of confounding by socioeconomic status”—meaning even after taking into account the fact that rich people eat more berries. The first population-based evidence that “greater intakes of blueberries and strawberries…were highly associated with slower rates of cognitive decline,” and not just by a little bit. “The magnitude of associations…were equivalent to the cognitive differences that one might observe in women up to 2.5 years apart in age.” In other words, “women with higher intake of berries…appeared to have delayed cognitive aging by as much as 2.5 years.”
Why not just take some kind of anthocyanidin supplement? Because there hasn’t been a single study that found any kind of cognitive benefit just giving these single phytonutrients. In fact, the opposite. “Whole blueberries appear to be more effective than individual components, showing that the whole is greater than the sum of its parts. These findings potentially have substantial public health implications, as increasing berry intake represents a fairly simple dietary modification to test in older adults for maintaining brain function.”
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