A type of plant pigment, quercetin is a flavonoid naturally present in many food and drink products which can also be taken in supplement form. This antioxidant is known to have anti-inflammatory properties, which could help reduce swelling, regulate blood sugar and protect against heart disease. Additionally, studies suggest that it might also aid in brain health, immune function and weight management.
Quercetin is beneficial for heart health in many ways. Not only can it decrease systolic and diastolic blood pressure, but it can also reduce pressure on arteries. High blood pressure can damage arteries and increase the risk of heart disease. Additionally, it has been demonstrated to decrease total cholesterol and triglycerides, which in excess, can pose a threat to heart health. Furthermore, it can also counteract oxidation, a process that changes “bad” LDL cholesterol and stiffens arteries. Finally, it can regenerate blood vessels to improve blood flow and support healthy heart function.
Few human studies have been conducted to assess the potential of quercetin in treating obesity; yet, the findings are encouraging. In a study with 6 men and 30 women who were overweight or obese, it was revealed that the quercetin group had considerable drops in weight, body mass index, waist, hip and thigh measurements, as well as in overall body fat percentage (particularly in the arms). To confirm the potential of quercetin in weight control and to understand its role in a weight management program, more research is required, with a greater number of participants.
Alzheimer’s disease (AD) is the most frequent form of dementia among seniors. It can lead to an impairment of memory and thinking skills over time.9 Flavonoids, the family of antioxidants to which quercetin is a member, have been studied for their antioxidant and anti-inflammatory activities. These are both beneficial for the prevention of AD.10 It has been demonstrated that flavonoids in general may help in the prevention or retardation of AD.
A study was conducted on humans, looking at the effect of quercetin-rich onion powder on cognitive function in 70 Japanese adults between 60 to 79 years old. The participants were divided into two groups, one of which received 11 grams of air-dried, high-quercetin onion powder each day for 24 weeks, while the other group was given a placebo.4 The results showed that quercetin-rich onion powder may be instrumental in delaying cognitive deterioration in elderly individuals with early stage AD.4 Moreover, the quercetin group experienced cognitive function scores, lessened depressive symptoms, and heightened motivation overall.
Although findings on quercetin and its impact on immune function have been inconsistent, there is some indication that it can support the immune system. In a trial of 1,002 participants, 500mg or 1000mg of quercetin or a placebo was taken each day for 12 weeks. There was no notable difference between the quercetin and placebo groups in terms of upper respiratory tract infections (URTI). However, those aged 40 and older who rated themselves as physically fit had fewer sick days and decreased severity of URTI symptoms. Furthermore, a separate small study among athletes revealed that supplementing with 100mg of quercetin per day did not have an effect on several measures of immune function after three days of intense exercise, but did reduce the risk of URTI. Notably, only one out of 20 participants in the quercetin group became ill during the two-week time frame following the exercise sessions, compared to nine of 20 in the placebo group.
A number of clinical trials have been conducted to evaluate the capability of quercetin in the prevention and treatment of COVID-19. One such study focused on 152 infected individuals, and discovered that the product made of quercetin and sunflower lecithin, which increases the rate of quercetin absorption by as much as 20 times, could lead to improvements in early symptoms and a lower risk of serious COVID-19 outcomes, such as hospitalization. Nevertheless, further investigations are necessary to securely determine the effectiveness of quercetin supplements against COVID-19. The NIH has included quercetin in its assessment of supplements for this virus, but there is not enough information to either support or deny the use of any supplement when preventing or treating COVID-19.
Even though a recommended daily intake for quercetin has yet to be established, it is suggested that adults consume 1.5 to two cups of fruit and two to three cups of vegetables per day. The US Food and Drug Administration also states that quercetin is safe in foods and drinks up to 500mg per serving. For those taking quercetin in supplement form, its safety and effectiveness of long-term use hasn’t been established, with only up to 1 gram a day for 12 weeks being considered safe.