Chapter 126
Other Berries
Most studies on the cognitive effects of blueberries have been conducted in children or younger adults, but a few tried the berries in older people. One study found that, for some reason, fish oil and blueberries together cancel out the boost in memory performance. Another study suggests that the berries protect against postoperative cognitive dysfunction. General anesthesia can scramble the memory of older people. One quarter to one third of people over 60 experience impairment of their cognitive function after general anesthesia, and it can last for weeks or months. Older people who were randomized to drink a little more than half a liter of blueberry juice per day for two weeks before planned major surgery suffered significantly less postoperative memory impairment than the others. We do know, however, that with a control group that consumes nothing, placebo effects cannot be ruled out. For some researchers, it is still too early for “definitive conclusions”; for them, blueberries should not yet “be administered in routine clinical practice.” But how much evidence do you need when it’s a healthy food anyway?
Other Berries
When rats develop learning and memory impairments from a high-fat diet, raspberries can improve some of them, and cherries also have positive effects. In a trial in humans, by contrast, tart cherry juice could not significantly improve outcomes compared with control beverages when taking into account the large number of variables tested. Cranberry juice also came up short. As I discuss in see.nf/mindberries, various berries were able to improve cognitive abilities in both young and old people, although the longest intervention study lasted only 24 weeks.
To see whether short-term improvements in cognitive abilities affect the brain’s aging process, we have to rely on observational studies that followed participants for many years. One study tracked the cognitive abilities of hundreds of twins for ten years and found that the anthocyanins from less than a quarter cup of blueberries daily, or about a cup of strawberries daily, slowed cognitive aging by four years. These findings suggest that eating a handful of berries a day—a simple treat—can slow brain aging. That’s one of the reasons I eat them for breakfast every day.
Plant Nitrates
Of 18 different food groups, one was associated with the smallest gradual loss of brain volume: vegetables. Large cohort studies went into more detail and showed that dark green leafy greens within the vegetable category offer the strongest protection against cognitive decline. Those who ate green vegetables daily had a 78 percent lower likelihood of cognitive impairment. The Rush Memory and Aging Project compared cognitive decline over five years in men and women averaging 81 years old who ate leafy greens daily with others who ate less than one serving per week, and made an extraordinary discovery. Are you sitting down? I quote from the study: “Those who ate one to two servings per day were, in terms of their rate of cognitive decline, eleven years younger than those who rarely or never ate leafy green vegetables.” But now that you’re sitting… go ahead and treat yourself to a big salad!
In the Harvard Nurses’ Health Study, the only category that seemed to stand out relative to leafy greens in terms of cognitive function was cruciferous vegetables like broccoli, cabbage, and cauliflower. Kale and kohlrabi were counted twice because they belong to both groups. Broccoli sprout juice or pure sulforaphane, the magnificent plant compound in cruciferous vegetables, show in vitro a broad range of neuroprotective effects against all sorts of things, from arsenic and carbon monoxide to pesticides and drugs that erase memory. In various Alzheimer experiments in rats and mice, sulforaphane proved directly protective, but until recently it had not been tested in humans.
In the 2021 study, older men and women were randomized to receive, daily for twelve weeks, the sulforaphane precursor equivalent to the amount in three cups of broccoli. The study provided the first direct evidence that cruciferous vegetables can improve working memory and processing speed. Population studies, however, also highlight other vegetables besides crucifers—spinach, for example, has even been called an “anti-Alzheimer plant.” So couldn’t other components of vegetables play a role as well? For example, nitrates?
As we age, blood flow to the brain decreases, affecting cognitive decline and the development of neurodegenerative diseases. The reduction in the amount of blood flowing through the brain may be due to an age-related decrease in the production of nitric oxide, that “open sesame” molecule that dilates blood vessels and thereby increases blood flow. Nitrate-rich vegetables like leafy greens and beets, however, ramp up nitric oxide production, which is one reason they can improve athletic performance. And what about cognitive performance?
At see.nf/braingreens you can find all the studies. But in essence, nitric oxide may improve not only brain function but perhaps even brain structure—connectivity more similar to that of younger adults. This is considered evidence for the potential improvement of neuroplasticity in older brains through nitrate-rich vegetables.
The Window to the Brain
Dark green leafy greens are also a source of concentrated carotenoids and vitamin K. In 100-year-olds, a higher level of plant vitamin K (phylloquinone, or vitamin K1) is associated with better cognitive function, but this is not the case for a higher level of animal vitamin K (menaquinone-4, a form of vitamin K2). The higher K levels in mentally fitter 100-year-olds could therefore just be an indication of green vegetable consumption. For example, the amount of plant vitamin K in the blood correlated with that of lutein, a carotenoid in leafy greens that accumulates in the human brain.
Because of its high fat content and high metabolic activity, our brain is particularly vulnerable to attacks by free radicals. And of course, we don’t want our brain to go rancid. In my video see.nf/brainlutein I discuss the importance of lutein for brain health, some of which has been established in autopsy studies. If only we could look into a living brain! We actually can—with our own eyes.
The retina, the back part of the eyeball, is actually an extension of the central nervous system, an outpouching of the brain during its development. And right in the middle there is a yellowish spot. We doctors see it when we shine a bright light into your eye. The spot, called the macula, is our HD camera, the place where we see at the highest resolution, and it’s packed with lutein (from Latin luteus for “yellow”). Since the amount of lutein in the retina corresponds to that in the brain, the eyes can be a window to the brain. The “macular pigment,” which consists of lutein and other green-plant carotenoids such as zeaxanthin, is directly related to scores on cognitive tests and to improvements in brain function and structure.
Where is the lutein? Avocado and egg producers like to boast about how much of these macular pigments are in their products, but the true superstar is dark green leafy greens. Half a cup of cooked kale contains 50 times more lutein than a hard-boiled egg; a spinach salad contains more than an omelet made from 50 eggs. Even studies funded by the Avocado Board could show no benefit from guacamole, whereas adding just 60 grams of spinach—about one fifth of a 250-gram package of frozen spinach—can significantly increase macular pigment in most people within a month.
As you can see in see.nf/luteintrials, lutein/zeaxanthin supplements can improve vision and cognitive abilities. But although they can contribute to preventing and treating one of the leading causes of age-related vision loss (see the chapter “Preserving Vision”), they do not seem able to do anything more once Alzheimer’s is present.
Lion’s Mane