The effects of Nordic berries on cognition and brain function: Connections with gut microbiota composition and cardiometabolic risk markers

An aging population is associated with an increased prevalence of cognitive decline and related diseases. Gradual cognitive decline is a natural feature of aging, but may also develop into a more severe loss of cognitive function, manifesting as mild cognitive impairment or severe cognitive disease. Currently, no medical treatments can fully prevent these conditions or diseases. One approach is to identify foods that have cognitive benefits to promote healthy aging in the population.

Emerging evidence suggests that consuming fruits high in polyphenols and fiber, such as berries, may help improve memory and cognitive function in humans and rodents. Nordic countries are abundant with wild berries, but the cognitive health benefits of these berries remain largely unexplored.

This thesis investigates the effects of Nordic berries on cognitive function in mice fed a high-fat (HF) diet, assessed by a series of behavior tests. The studies also aim to explore other health effects of berry supplementation, such as the impact on levels of cardiometabolic risk markers and gut microbiota composition. Additionally, this thesis also examines a potential probiotic – Prevotella copri DSM18205^T – and assesses its ability to utilize various carbon sources including the carbohydrate constituents in the berries investigated in the thesis.

The results suggest that lingonberry, bilberry, blackcurrant, cloudberry, and blueberry positively affect brain function in middle-aged HF-fed C57BL/6J mice, as demonstrated by improved performance in the T-maze alternation test. Additionally, a berry mixture containing lingonberries and bilberries significantly improved spatial and learning memory in C57BL/6J mice, as seen in their enhanced performance in both the T-maze and the Barnes maze tests.

Supplementation of the berry mixture to a HF diet may aid in reducing body weight, fasting insulin as well as neuroinflammation levels in C57BL/6J mice. In addition, in apolipoprotein E knockout mice (ApoE–/–) a HF diet including lingonberries significantly reduced body weight and improved glucose response. An additional finding is that berries strongly influence the composition of the gut microbiota, promoting the relative abundance of the bacterium Akkermansia muciniphila, which has previously been linked to protective effects on cognition. The work in this thesis also revealed the growth characteristics and cultivation techniques of P.copri DSM18205^T.

The significance of these findings provides recommendations for dietary strategies that incorporate berries, these strategies may aid in mitigating the growing prevalence of cognitive decline and diseases associated with the aging global population. Lastly, the knowledge gained on the growth and metabolite characteristics of P.copri DSM18205^T will provide a basis for future research on its potential uses.