Written by Alexa Heathorn, MS, CNS-c, Science Writer. Daily intake of 110 mg of quercetin glycosides for 40 weeks improved reaction time and preserved brain blood flow in older adults, suggesting quercetin may help support healthy cognitive aging.

Age-related cognitive decline is an escalating global health concern. According to the World Health Organization, dementia currently affects an estimated 50 million people worldwide, with approximately 10 million new cases diagnosed each year¹. Mild cognitive impairment (MCI), often considered a transitional stage between normal aging and dementia, progresses to dementia in 5–15% of cases annually¹. While genetics and aging play key roles, many contributing factors to cognitive decline are modifiable including diet, physical activity, sleep quality, and mental health¹. As such, early prevention strategies targeting these lifestyles are important for preserving cognitive health. A recent randomized, double-blind, placebo-controlled study explored one such strategy of daily quercetin glycoside supplementation on cognitive performance and cerebral blood flow in older adults¹.

Quercetin is a flavonoid found in onions, broccoli, and tea. It possesses antioxidant, anti-inflammatory, and vasoprotective properties, which may contribute to its role in supporting cognitive function². Research has shown that diets rich in flavonoids are associated with lower rates of cardiovascular disease, improved vascular health, and reduced oxidative stress, all factors closely tied to brain aging and neurodegeneration¹. Despite its potential, quercetin’s poor absorption and bioavailability have limited its clinical use. To overcome this, researchers developed quercetin glycosides, a modified form in which glucose is bound to quercetin, allowing it to be more efficiently absorbed in the small intestine. Previous studies suggest that quercetin supports vascular endothelial function, reduces amyloid-β accumulation, and modulates insulin-like growth factor-1 (IGF-1), all mechanisms that may protect against cognitive decline¹. This study aims to assess if the effects of improving cerebral blood flow (CBF) and oxygen delivery to the brain by quercetin glycosides could help maintain cognitive performance in aging populations¹.

The study enrolled 80 Japanese adults aged 60–80 years who were aware of age-related cognitive decline but had no diagnosis of cognitive impairment. Participants were screened to exclude those with neurological or psychiatric disorders, severe anemia, or irregular lifestyles, as well as those using supplements or medications that could affect cognitive function. Individuals who regularly consumed large amounts of onions or alcohol, or smoked excessively, were also excluded. Eligible participants were randomly assigned to one of two groups. The active group receiving 500 mL of barley tea containing 110 mg of quercetin glycosides (as isoquercitrin) or the placebo group receiving 500 mL of identical barley tea without quercetin. Both groups consumed their assigned beverage daily for 40 weeks. Cognitive function, cerebral blood flow, and quality of life were measured at baseline and at the end of the study to determine whether long-term quercetin intake could enhance brain function and blood flow compared to placebo¹.

After 40 weeks, participants who consumed the quercetin-enriched beverage showed several measurable improvements compared to the placebo group:

• Reaction Time: The quercetin group demonstrated a significant improvement in reaction time (mean +4.0 ± 10.7) compared to the placebo (+0.5 ± 8.6; p = 0.037), indicating enhanced processing speed and attention.
• Overall Cognitive Function: Within the quercetin group, composite scores for cognitive flexibility, executive function, and psychomotor speed improved from baseline, though between-group differences were not statistically significant.
• Cerebral Blood Flow (CBF): Measurements using near-infrared spectroscopy (NIRS) revealed that total hemoglobin (Hb) and oxygenated hemoglobin (O₂Hb) concentrations in the left frontal cortex—a region sensitive to cognitive stress—significantly declined in the placebo group but remained stable in the quercetin group, suggesting that supplementation helped preserve cerebral blood flow.
• Insulin-Like Growth Factor-1 (IGF-1): Serum IGF-1 levels significantly increased in the quercetin group, which may support neuronal growth and neuroprotection.
• Amyloid-β Accumulation: Both groups showed slight increases in amyloid-β (Aβ) ratios over time, but this change was less pronounced in the quercetin group, implying a potential protective effect against Aβ buildup.
• Quality of Life: Within-group analysis showed notable improvements in mental vitality and emotional well-being among quercetin participants, consistent with reduced stress and improved brain activity.

Potential limitations of the study include:

• The study population was limited to healthy Japanese adults aged 60–80, therefore results may not be generalizable to individuals outside of this age range, or to those with diagnosed cognitive disorders or advanced dementia.
• The trial was conducted during the COVID-19 pandemic, a period associated with heightened stress and lifestyle disruption, which may have influenced certain outcomes related to mood, cognition, or sleep.
• Participants generally had high baseline cognitive scores, which may have reduced the ability to detect between-group differences in overall cognitive performance.
• The sample size was relatively small, limiting statistical power, and while trends favored quercetin supplementation, some findings did not reach significance.
• Quality-of-life and stress-related outcomes were based on self-reported data, which may introduce bias or variability in individual responses.

Daily supplementation with 110 mg of quercetin glycosides as isoquercitrin for 40 weeks improved reaction time, preserved cerebral blood flow, and enhanced mental vitality in older adults experiencing age-related memory decline. These findings suggest that quercetin glycosides may help support healthy cognitive aging and maintain brain function through mechanisms involving improved vascular function, increased IGF-1 levels, and suppression of amyloid-β accumulation. Overall, quercetin glycosides appear to be a safe and promising nutritional intervention for sustaining mental performance and vitality in aging adults. However, larger and longer-term studies are needed to confirm these effects and to better understand their potential applications in individuals with mild cognitive impairment or early-stage dementia.

Source: Nakamura, Y., H. Watanabe, A. Tanaka, J. Nishihira, and N. Murayama. “Effect of quercetin glycosides on cognitive functions and cerebral blood flow: a randomized, double-blind, and placebo-controlled study.” European Review for Medical & Pharmacological Sciences 26, no. 23 (2022).

Click here to read the full text study.

Posted November 7, 2025.

Alexa Heathorn, MS, CNS-c, is a clinical nutritionist specializing in metabolic health, hormonal balance, and gastrointestinal restoration through root-cause functional nutrition. She earned her master’s degree in Nutrition from Bastyr University and is currently a Certified Nutrition Specialist (CNS) candidate. Alexa also works as a research writer and functional health consultant, translating complex science into actionable strategies for practitioners and wellness companies. Learn more at www.bloomedwellness.com.

References:

1. Nakamura Y, Watanabe H, Tanaka A, Nishihira J, Murayama N. Effect of quercetin glycosides on cognitive functions and cerebral blood flow: a randomized, double-blind, and placebo-controlled study. Eur Rev Med Pharmacol Sci. Dec 2022;26(23):8700–8712. doi:10.26355/eurrev_202212_30541
2. Chiang MC, Tsai TY, Wang CJ. The Potential Benefits of Quercetin for Brain Health: A Review of Anti-Inflammatory and Neuroprotective Mechanisms. Int J Mol Sci. Mar 28 2023;24(7)doi:10.3390/ijms24076328