Strawberries may reduce dementia risk and boost mood in people whose age and metabolic health predispose them to cognitive decline.
A 12-week study found that middle-aged overweight people with signs of insulin resistence who ate the equivalent of one cup of strawberries each day had better memory and fewer depressive symptoms compared to a control group.
In addition to dementia, metabolic disturbances like insulin resistance, obesity, and related health issues are becoming more common. Lack of sensitivity to the insulin hormone affects nearly half of the US population over the age of 60, and it's a risk factor for dementia later in life.
"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," says neuroscientist Robert Krikorian from the University of Cincinnati.
Krikorian and his team in the US recruited 30 adults, mostly women, aged 50 to 65 with mild cognitive impairment and a body mass index (BMI) that placed them in the overweight category.
They were asked to avoid berry fruit consumption of any kind for two weeks prior to the study, while during the study they were given either a 13-gram supplement powder of real strawberries or a placebo to eat each day. Participants' executive abilities, word retrieval, long-term memory function, and mood were all assessed via cognitive tests before and after the study, and the researchers tracked metabolic data.
Those who were given the placebo didn't do as well on a delayed recognition test, which measures something called memory interference. However, memory interference was reduced in those given strawberry powder, suggesting that they were better able to ignore unimportant data.
"Reduced memory interference refers to less confusion of semantically related terms on a word-list learning test," Krikorian explains. "This phenomenon generally is thought to reflect better executive control in terms of resisting intrusion of non-target words during the memory testing."
Participants given strawberry powder also reported lower depressive symptoms, indicating improved emotional coping and executive capability; that is, better ability to manage everyday activities and social relationships and improved response control and greater flexibility.
The researchers note that age and insulin resistance are likely to have mildly impaired executive function in many of the participants, suggesting the 'treatment' corrected existing deficiency to some extent. They don't know if strawberries would improve function in those without impairment.
"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 adds.
"Thus, the beneficial effects we observed might be related to moderation of inflammation in the strawberry group."
A 2022 study by the same researchers and some colleagues found that in a similar cohort of people, those who ate blueberries every day had reduced levels of memory interference.
"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," says Krikorian.
"The unexpected absence of benefit with regard to metabolic function might reflect the lower dose of anthocyanins used in this study as compared with other trials investigating metabolic and cognitive function," the team writes.
Krikorian and team can't draw broad conclusions from their findings due to the small sample size, short duration, and limited regulation of the participants' diets. Studying the effects of foods – which are never consumed in isolation – on health is difficult, as our bodies are complex with intricate nutritional requirements.
Possible cognitive benefits aside, experts generally recommend a diverse and balanced diet – which can include strawberries as a great source of vitamin C – as the best approach to get the vitamins, minerals, and nutrients we need.
"These considerations highlight the need for further investigation of health and neurocognitive benefits associated with strawberry supplementation employing different dosages, larger samples, and intervention periods of varying lengths," the authors conclude.
The study has been published in Nutrients.