Can polyphenols prevent our brains from slowing down?

As the human body ages, its natural metabolic processes tend to create more oxidative stress^[1] while simultaneously losing the ability^[2] to dampen it. This imbalance can lead to^[3] chronic inflammation and tissue damage and is associated with chronic disease^[4] such as cancer, cardiovascular diseases, and neurodegenerative diseases.

While the cause of neurodegeneration is complex and likely involves many factors, multiple studies have suggested oxidative stress as a prominent factor and nutrition (specifically plant-based foods^[5]) as a preventive measure^[6] for age-related cognitive decline. Age-related cognitive decline^[7] manifests itself as a dwindling in memory, attention capacity, processing speed, and executive function (cognitive control of behavior)—all of which can be indicators of neurodegeneration^[8].

Polyphenols^[9], shown in Figure 1, are compounds that are generally not directly involved in the growth, development, or reproduction of plants, but confer protection against ultraviolet radiation, pathogens, and oxidation. They are commonly found in fruits and vegetables and their byproducts (e.g., red wine, dark chocolate, tea, etc.). Polyphenols have demonstrated potent antioxidant and anti-inflammatory activity and their intake is associated^[10] with a decreased risk of chronic diseases.

Figure 1: Polyphenols in a nutshell

References: Losada-Echeberría et al. Antioxidants (Basel). 2017 Nov.^[11] Phenol-Explorer: http://phenol-explorer.eu/

Recent studies have reported improvements in various measures^[12] of cognitive function^[13], as well as biomarkers of neuroplasticity^[14] and neuroinflammation^[15], from various sources of polyphenols. However, there are few studies on many different sources, doses, and durations of polyphenol supplementation and some studies have demonstrated somewhat^[16] conflicting results^[17] and relatively small sample sizes. This led the researchers of the study under review to conduct a systematic review and meta-analysis in an attempt to resolve the uncertainties regarding the impact of polyphenol intake on cognitive function in older people.

Greater oxidative stress is a prominent factor involved in age-related cognitive decline. Polyphenols are plant compounds with antioxidant and anti-inflammatory properties that may reduce the impact of aging on cognitive function. A high variety of polyphenol sources and cognitive tests, small sample sizes, and somewhat conflicting results in the existing literature led researchers to conduct a systematic review and meta-analysis in an attempt to resolve uncertainty regarding the impact of polyphenol intake on cognitive function.