Strawberries may help reduce memory loss and depression in middle-aged adults who have an increased risk of developing dementia, according to a new study published in Nutrients.
Alzheimer’s disease is a common and incurable form of dementia often beginning in midlife with symptoms progressing over many years. Metabolic dysfunction is also prominent during the midlife period, leading to increased rates of insulin resistance, hyperinsulinemia (higher-than-normal blood insulin levels) and obesity.
Disturbances to metabolism creates an environment of inflammation in the brain, which is thought to be one mechanism contributing to Alzheimer’s disease.
Strawberries and other berry fruits are rich in anthocyanins, natural compounds that give them their red color. Studies have demonstrated anthocyanins reduce inflammation, as well as corrects metabolic dysfunction, and that strawberry supplements in general have improved metabolic function, cognitive performance, and overall health.
Consequently, researchers from the University of Cincinnati led by Robert Krikorian sought to investigate the effects of strawberry supplementation on cognitive function, mood, and metabolic health in middle-aged adults with increased risk for developing dementia – in particular, overweight individuals with insulin resistance and mild subjective cognitive complaints.
A randomized, double-blind, placebo-controlled trial was conducted with 30 participants aged 50 to 65 years old.
The participants were randomly assigned to receive either daily packets of 13 grams strawberry powder from desiccated, freeze-dried, and milled whole strawberries (15 participants), or placebo powder (15 participants) for 12 weeks. The participants were instructed to avoid consuming any other berry products during the study and to complete diet diaries before and after being given the powder.
The participants underwent an array of cognitive and mood assessments, blood tests to measure metabolism, and body measurements (e.g. height and weight) at the start of the study, and after 12 weeks.
The researchers discovered that strawberry supplementation did not affect executive ability (planning and execution of goals), lexical access (recognizing words from a ‘mental dictionary’ when wanting to use/understand the word), verbal memory (remembering words and language-based information), or visual-spatial memory (a ‘mental map’ that stores information on where objects are).
However, the strawberry powder was found to reduce memory interference and depressive symptoms compared to the placebo powder.
Memory interference refers to the difficulty in learning and remembering new information due to the presence of irrelevant or competing information. The researchers suggested that these benefits may reflect improved executive control, which allows suppression of the irrelevant information.
Depressive symptoms include feelings of hopelessness, irritability, and guilt. Krikorian and colleagues suggested that the group who received the strawberry supplements had “improved emotional coping capability and lower levels of stress. Such coping enhancement also can be understood as implying improved executive ability, i.e. better ability to manage everyday activities and social relationships and improved response control and greater flexibility.”
Strawberry supplementation did not affect metabolic health, as no differences were found between the groups for fasting glucose levels, insulin levels, HOMA-IR (assessment of the degree of insulin resistance), glycated hemoglobin (a marker of average blood glucose levels), triglycerides (fat) and high density lipoprotein cholesterol. Body weight, BMI, and waist circumference also did not differ between the groups.
The researchers noted that this finding was in contrast to their original hypotheses and suggested that perhaps “the cognitive and mood effects were not attributable to enhancement of metabolic function as we expected. It may be that anti-inflammatory actions of anthocyanins were effective in correcting aspects of neurocognitive deficit in the absence of improvement of metabolic health”.
The researchers speculated that the lack of effect on these measures may be due to the limitations of a small sample size, the short period of the study, or the relatively low anthocyanin dose provided by the strawberry powder compared to other fruits such as blueberries where doses are in higher quantities.
The study, “Early Intervention in Cognitive Aging with Strawberry Supplementation“, was authored by Robert Krikorian, Marcelle D. Shidler and Suzanne S. Summer.