Nutritionists have long recommended strawberries as a great source of vitamin C, antioxidants and fiber that helps maintain a healthy metabolism. Despite their sweetness, strawberries also are naturally low in sugar — making them a preferred alternative to other treats that may increase the risk of diabetes.
A growing body of research shows that eating strawberries also may be effective at slowing cognitive decline and the progression of dementia among middle-aged adults. Those with mild impairment may see improved mental performance and sharper memory by making strawberries a regular part of their diets.
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At the University of Cincinnati, researchers sought to test whether strawberries have similar cognitive benefits to those they found in a study they did last year on blueberries. In that study, the researchers found evidence that blueberries may lower the risk of late-life dementia in middle-aged people. The benefits appear to be linked to the antioxidants that give the berries their distinctive colors.
"Both strawberries and blueberries contain antioxidants called anthocyanins, which have been implicated in a variety of berry health benefits such as metabolic and cognitive enhancements," said Robert Krikorian, professor emeritus at UC's medical school. "There is epidemiological data suggesting that people who consume strawberries or blueberries regularly have a slower rate of cognitive decline with aging."
In both studies, the researchers recruited groups of overweight, middle-aged people ages 50-65 to test whether adding the berries to their diets would improve their scores on cognitive tests.
The strawberry study included 30 people with complaints of mild cognitive decline, because this group tends to be at higher risk of dementia and other common conditions.
Mild cognitive impairment is an under-the-radar condition that often is a precursor to more serious declines in memory and the development of dementia. According to the Alzheimer's Association, an estimated 12-18% of people over 60 live with mild cognitive impairment. Symptoms include forgetfulness of basic daily experiences, conversations and plans that previously had been easy to recall. MCI also can affect the ability to make sound decisions and develop strategies to carry out tasks.
Many people with MCI may not get screened for it before the disease progresses. Once a diagnosis is made, about 10-15% of people with the condition go on to develop dementia within just one year, Yale Medicine reported last year.
The strawberry study participants were asked to abstain from eating any berries for 12 weeks – except for a daily packet of supplement powder to be mixed with water and taken with breakfast. Half of the participants got a powder that contained the equivalent of one cup of whole strawberries, the standard serving size. The other participants were given a placebo.
Those that ate the strawberry powder showed lower levels of memory interference, a type of cognitive impairment that makes it hard for people to recall specific information drawn from similar memories. In people with high levels of memory interference, similar long-term memories compete with one another and make it difficult to access information in the form of short-term recall. As this problem progresses, some long-term memories can be completely forgotten.
The study participants who took strawberry powder also had lower levels of depressive symptoms. The researchers believe this is related to overall better executive functioning in the brain that enables better emotional control, coping and problem-solving.
The researchers said the improvements in the strawberry powder group could be the result of reduced inflammation in the brain.
"Executive abilities begin to decline in midlife and excess abdominal fat, as in insulin resistance and obesity, will tend to increase inflammation, including in the brain," Krikorian said. "So, one might consider that our middle-aged, overweight, prediabetic sample had higher levels of inflammation that contributed to at least mild impairment of executive abilities. Accordingly, the beneficial effects we observed might be related to moderation of inflammation in the strawberry group."
The study builds on previous research that linked greater intake of strawberries and blueberries to slower rates of cognitive decline in older people.
Although the study group at the University of Cincinnati was small, Krikorian and his colleagues hope to expand their research in the future with more participants and varying doses of strawberry supplements.