Quercetin is one of the most extensively distributed dietary flavonoids in vegetables and fruits. Quercetin has been shown to possess anti-inflammatory, antioxidative, anti-viral, and neuroprotective properties in both human and animal studies. 

According to a recent double-blind, placebo-controlled, randomized clinical trial published in Phytotherapy Research, quercetin supplementation had beneficial effects on antioxidant status, inflammatory factors, and quality of life (QOL) in post–myocardial infarction (MI) patients. This trial included 88 post-MI patients. Half of the patients received 500 mg/day of quercetin and the other half received a placebo for 8 weeks. After 8 weeks, the treatment group had significant increases in total antioxidant capacity (TAC) compared to a placebo. Tumor necrosis factor-alpha (TNF-α) levels and insecurity scores were significantly reduced in the quercetin group. However, no significant changes were seen between the treatment group and the placebo group for interleukin (IL)-6, high-sensitivity C-reactive protein, blood pressure, and other quality of life dimensions. These results suggest that quercetin may support those patients with cardiovascular conditions. 

Myocardial infarction, commonly known as a heart attack, is one of the leading causes of morbidity and mortality worldwide. This condition gives rise to a local and systemic inflammatory response that further perpetuates damaged myocardial tissue and increases the risk of recurrent ischemic events, along with myocardial cell apoptosis. 

Evidence from another recent comprehensive systematic review published this June in Phytomedicine indicates that quercetin supplementation may have positive effects on sepsis by mitigating oxidative stress and inflammation. These conditions and their symptoms are caused by the inability of the patient to respond properly to infection, and thus, the sepsis is often fatal. The results from the review showed that quercetin supplementation downregulates messenger RNA expression of toll-like receptors, which play a critical role in the innate immune response. The review results also indicated that activation of pro-inflammatory transcription factors, such as nuclear factor (NF)-κB, thereby modulate the immune response and attenuate sepsis-related organ dysfunction. Larger human clinical trials are needed to further support the use of quercetin in sepsis complications.

Due to the anti-inflammatory properties demonstrated by quercetin, supplementation may be helpful in supporting a healthy inflammatory response within other organ systems, such as the digestive system. Quercetin may also support individuals with inflammatory bowel diseases (IBD), such as ulcerative colitis.

In a mouse model of IBD, quercetin enhanced beneficial colonic microbial diversity and alleviated colitis severity by suppressing the production of pro-inflammatory cytokines, IL-17, IL-6, and TNF-α, and promoted the production of IL-10 (a cytokine with potent anti-inflammatory properties) in colonic tissue compared to control mice. The results of this animal study suggest that quercetin may help protect the gut’s mucosal immune system with IBD patients by altering the intestinal microbiome and reducing inflammatory factors that are linked to colonic damage seen in the pathogenesis of IBD.      

Fortunately, quercetin can be found abundantly in fresh fruits and vegetables, and supplementation is inexpensive. Rich dietary sources of quercetin include onions (especially red onion), apples, red grapes, dark berries, cherries, citrus fruits, green tea, and cruciferous and green leafy vegetables. It is recommended for patients with these inflammatory conditions to add quercetin to their daily supplements regimen to help support a normal immune and inflammatory response. 

By Caitlin Higgins, MS, CNS, LDN