Specifically, scores for tests assessing orientation, visuospatial/executive and language, and recall were all improved when compared to the placebo. In addition, scores for quality of life and functional capacity also saw increases following supplementation.
“Therefore, the consumption of 50g of raisins produces a slight improvement in cognitive performance, quality of life, and functional activities in the elderly,” the ‘Nutrients’ published report concludes.
The researchers add: “This study can also affirm that flavonoids, present in raisins, may be related to better cognitive performance.”
It has been observed that diets rich in fruit and vegetables can result in a reduced prevalence of inflammatory and neurodegenerative diseases, due to their high phenolic contents. Such compounds, including polyphenols, are known to have potent anti-inflammatory and antioxidant activities.
Following this, studies have suggested that nutritional interventions with phenolic compounds may prevent cognitive decline associated with age, due to their influence on the pathological mechanisms underlying cognitive degeneration.
Grapes are noted to be particularly rich in such polyphenols, containing a diverse array of anthocyanins, flavanols, hydroxycinnamic acid, and flavonols, with previous studies noting the neuroprotective properties associated with their consumption.
Raisins offer a low glycaemic index alternative whilst providing satiety, yet little research has been conducted into their supplementation with regards to the effects on cognitive health. Thus, the researchers sought to investigate this potential relationship.
The clinical trial involved the recruitment of 80 participants aged over 70 years old, who were randomised into an intervention or a control group. The intervention group were administered 50g of Málaga muscatel raisins per day (equating to 9.48mg of polyphenols) in addition to their usual diet over a six-month period.
Cognitive performance was measured at baseline and at six months, which was assessed using the Montreal Cognitive Assessment (MOCA) and Mini Mental State Examination (MMSE) test. Recall responses were also assessed using the Rey Auditory Verbal Learning Test.
It was reported that scores from the MOCA test resulted in a 3.27 point difference in favour of the supplemented group. In addition, the MMSE test scores showed an improvement by 0.36 points after the 6-month period. These outcomes suggested an improvement in cognitive performance, visuospatial/executive capacity and language.
Furthermore, immediate and delayed recall responses also improved within the supplemented group, as well as improved scores for quality of life by 1.21 points and autonomy in instrumental activities of daily living by -0.21 after 6 months.
“The results of this study suggest that the supplement of 50g of Málaga muscatel raisins slightly improves cognitive performance, specifically orientation, visuospatial/executive capacity, language, the overall MOCA test score, and immediate and delayed recall,” the report concludes.
The researchers highlight the potential limitations of the study, such as the lack of participant blinding as well as the potential learning effect introducing bias. Therefore, they urge future studies to consider these factors, and further investigate the mechanism of action behind the effects of polyphenols on cognition.
They hypothesise: “The exact mechanism by which polyphenols provide such positive effects is not exactly known, but the consumption of compounds from the families of flavanols and stilbenes, present in a large number of foods of vegetable origin, such as tea, cocoa, grapes, and red wine, has been shown to improve the bioavailability of nitric oxide.
“This compound produces an increase in vasodilation and with it improves cerebral perfusion. Therefore, it is believed that they could counteract neuroinflammation. Underlying mechanisms involving the microbiota-gut-brain axis have also been described.”
“Effects of a Raisin Supplement on Cognitive Performance, Quality of Life, and Functional Activities in Healthy Older Adults—Randomized Clinical Trial”
by María José Rodrigo-Gonzalo, Susana González-Manzano, María Carmen Pablos-Hernández, Roberto Méndez-Sánchez, Begoña Ayuda Duran, Jesús González-Sánchez, Fausto Barbero-Iglesias, Ana María González-Paramás and José Ignacio Recio-Rodríguez