Anthocyanins, a flavonoid subclass present in certain blue, purple and red fruits and vegetables, have potential neuroprotective properties due to their anti-inflammatory, antioxidant, and signalling effects (1). Clinical and epidemiological studies of anthocyanins provide promising evidence for attenuation of memory loss and improved cognitive function (2). We investigated the effects of anthocyanins, provided through diet or supplementation, on cognitive function and related parameters (3). A multi-centre, 24-week randomised, parallel 3-arm clinical trial was conducted in participants aged 60-85y with self-reported memory complaints and scoring ≤13 on the Memory Index Score within the Telephone Montreal Cognitive Assessment (T-MoCA). Participants were randomised to high anthocyanin diet, freeze-dried product derived from blackcurrants (250mg anthocyanins/day), or control (placebo). The primary outcome was auditory episodic memory functioning. Secondary outcomes were additional cognitive functions, subjective memory complaints and self-reported depression symptoms, blood pressure, inflammatory biomarkers, lipid profile, vascular and microvascular endothelial function tests, and gut microbiota. Mixed linear modelling evaluated changes over time. Gut microbial abundance (alpha diversity) was measured using Shannon Simpson’s Index and association between anthocyanin intake and taxa level was assessed using the MaAsLin2 multivariable regression model. Of 110 participants enrolled (mean age 69.2 y SD 6.7; 36 males, 74 females), 94 completed the study. Median anthocyanin intake increased by 76.7 mg, 252.1 mg, and 2.9mg in the diet, active powder, and control groups, respectively. There was no treatment*time effect on any primary or secondary outcomes. A time effect was observed for the majority of psychometric tests. At baseline, participants with habitual anthocyanin intake ≥10mg/day performed better on a number of cognitive tests compared to those with higher intakes (P<0.05). They also had a clear difference in microbial abundance with Bacteroides sp. enriched in the higher anthocyanin group, compared to Enterococcus sp. enriched in the lower anthocyanin group. The active powder group had an increase in alpha diversity (P = 0.074) at follow-up which was more pronounced in in participants with a low habitual anthocyanin intake at baseline. In conclusion, this clinical trial found no significant effect of dietary or supplemental anthocyanins, on any of the investigated outcomes in older adults with self-reported memory complaints, except potential improvements in the gut microbiome in the active powder group. We postulate that the potential anti-inflammatory, antioxidant, and signalling effects of anthocyanins were insufficient to significantly modulate any outcomes due to participants’ overall good health and lack of relevant cognitive decline. We recommend future interventional studies focus on subjects with low habitual anthocyanin intakes, those with diagnosed cognitive impairment, such as Mild Cognitive Impairment and dementia, and those with more severe comorbidities, particularly chronic inflammatory conditions.
Trial Sponsor: National Health and Medical Research Centre (NHMRC) Dementia Collaborative Research Centre.