Strawberries are known to contain anthocyanins, but they are also rich in ellagitannins and ellagic acid – polyphenols that have been associated with health benefits.
The research, published in the journal Nutrients, observed the effect of strawberry powder supplementation on middle-aged subjects and found diminished memory interference among strawberry-treated participants as well as fewer depressive symptoms – benefits consistent with improved executive ability.
Robert Krikorian, professor emeritus in the University of Cincinnati’s Department of Psychiatry and Behavioral Neuroscience, said: “Reduced memory interference refers to less confusion of semantically related terms on a word-list learning test. This phenomenon generally is thought to reflect better executive control in terms of resisting intrusion of non-target words during the memory testing.”
The strawberry-treated participants also reported a significant reduction in depressive symptoms, which Krikorian said could be understood to result from “enhanced executive ability that would provide better emotional control and coping, and perhaps better problem-solving”.
Berry health benefits extend to blueberries
The study, which was supported by the California Strawberry Commission, adds to previous findings from the same research group; in 2022, they found that adding blueberries to the daily diets of middle-aged populations may lower the chances of developing late-life dementia.
“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 Krikorian. “There is epidemiological data suggesting that people who consume strawberries or blueberries regularly have a slower rate of cognitive decline with ageing.”
Rates of insulin resistance, commonly known as prediabetes, vary worldwide but are increasing; in the US, about 50% of individuals develop insulin resistance around middle age, which has been shown to be a factor in chronic diseases.
Strawberry consumption has been studied previously for its metabolic and cardiovascular benefits, but there have been relatively few studies on its cognitive effects, according to Krikorian.
“This study assessed whether strawberry consumption might improve cognitive performance and metabolic health in this population and, if so, whether there might be an association between cognitive enhancement and reduced metabolic disturbance,” he said.
Strawberry-supplemented group report fewer memory problems
Thirty overweight patients, aged between 50 and 65 years, with complaints of mild cognitive decline were enrolled in the study. Krikorian said this population has an increased risk for late-life dementia and other common conditions.
Participants were asked to abstain from berry fruit consumption of any kind for 12 weeks apart from a daily packet of supplement powder, to be mixed with water and consumed with breakfast. Half of the group received powders containing the equivalent of 13 g whole strawberries (the standard serving size), while the others received a placebo.
Subjects were tested on cognitive abilities such as long-term memory; the researchers also tracked their mood, intensity of depressive symptoms, and metabolic data over the course of the study.
Those in the strawberry powder group reported diminished memory interference, and a reduction in depressive symptoms.
“This controlled trial showed that daily supplementation with 13 g whole fruit strawberry powder reduced interference in memory and depressive symptoms in overweight middle-aged individuals,” the authors wrote. “These findings were understood as manifestations of improved executive control.”
While more research is needed, Krikorian said strawberry supplementation may have improved cognitive function by reducing 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,” he 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.”
Unexpected lack of effect on metabolic health
Other research on strawberries has found improvement in metabolic measures, including lower insulin levels, but no effect on the patients’ metabolic health was found in this study.
“Those studies generally used higher dosages of strawberry powder than in our research, and this could have been a factor,” Krikorian said.
Future research trials should include larger samples of participants and differing dosages of strawberry supplementation, he suggested.
