Flavonoids: 5 things to know before taking supplements

Flavonoids are chemicals found in plants, but they have an array of curious effects on the human body. Research suggests they may be beneficial for our health and our mental health. And because they are so botanically ubiquitous, we are consuming them all the time.

But while they are common components of a balanced diet, some people choose to take flavonoid supplements to boost their intake. Here are five facts you need to know before you decide to reach for the pill bottle.

What are flavonoids?

Flavonoids are a diverse class of chemical compounds created by plants. They are considered to be “secondary metabolites,” as they are not directly involved in growth and development. Instead, they serve other purposes such as pigmentation, UV protection, and fighting off harmful microbes.

About 6000 varieties of flavonoid have been identified so far.

Extracted from plants, these chemicals are used to create pharmaceutical, medical, agricultural, and cosmetic products.

What foods have flavonoids?

Flavonoids are abundant in plant-based foods. They are divided into several subcategories, which include flavones, anthocyanidins, isoflavones, and flavanols.

You've probably read headlines about red wine and chocolate being good for you in small doses — the reason why may be because they both are rich in flavonoids.

Some common foods that contain flavonoids include:

• Fruits
• Vegetables
• Herbs such as chamomile, peppermint, and rosemary
• Olive oil
• Tea
• Cocoa
• Wine
• Soy and fava beans
• Rice bran
• Nuts
• Vinegar

What do flavonoids do in the body?

Shortly, a lot. Research suggests flavonoids have anti-inflammatory, anti-carcinogenic, and antioxidative effects, as well as positive effects on the cardiovascular system. Some flavonoids are being investigated as treatments for metabolic problems, diabetes, Alzheimer’s, antibiotic-resistant infection, and the H1N1 flu.

According to a review published in the Journal of Nutritional Science, their antioxidant effects — the ability to both reduce and scavenge harmful atoms called free radicals in the body — generate the most interest from the scientific community, and thus have the greatest evidence base.

“Almost every group of flavonoids has a capacity to act as antioxidants,” write the authors.

Free radicals are produced naturally by the body during oxygen metabolism, and can go on to damage cellular membranes and even destroy cells. Our bodies produce antioxidants to help neutralize these destructive wanderers. Researchers believe we can get even more antioxidant support from eating foods rich in flavonoids.

What do flavonoids do in the brain?

In November 2020, researchers published the results of a small study demonstrating that flavanols (a subcategory of flavonoids) improved cognitive function and elevated brain oxygenation levels in response to a stress event.

In the study, participants breathed air with carbon dioxide concentrations 100 times higher than found in normal air — essentially starving their body of oxygen. Before and after the test, participants drank a cocoa beverage. Each participant completed the test on two occasions. During one of the tests, the cocoa beverage contained low levels of flavanols, and the other contained high levels of flavanols. After the test, the participants completed a series of increasingly complex cognitive tests.

Participants who had ingested the high-flavanol beverage recovered from the carbon-dioxide stress test faster and better than those who consumed the low-flavanol drink. High-flavanol drinkers also completed the high complexity cognitive tests with increased speed and accuracy, completing the most complex tasks an average of 11 percent faster than low-flavanol drinkers.

Catarina Rendeiro is the lead author on the study and a Lecturer in Nutritional Sciences at the University of Birmingham's School of Sport, Exercise and Rehabilitation Sciences.

“We have known for many years that flavanols from cocoa in particular can improve vascular function in humans by improving vessel [and] arterial function," Rendeiro tells Inverse.

"These benefits are apparent even after only one single dose. However, the extent to which some of these benefits could translate into the brain vasculature were less clear. Hence the goal of this study,” she says.

The findings jibe with older studies investigating flavonoids and their effect on cognition, but more work is needed to tease out whether they improve cognitive function or perhaps stave off cognitive decline.

There is also some evidence to suggest flavonoids could help treat psychiatric conditions, including depression. In one 2017 paper, researchers found flavonoid supplements may act in compliment to traditional therapies for depression, but that more work was needed to fully understand what effect flavonoids have on the condition.

Do flavonoid supplements work?

Widely available flavonoid supplements include quercetin, curcumin, silymarin, green tea extracts, and rutin.

The science suggests flavonoid supplements are capable of having an effect on the body, but what those effects are, how desirable they may be, and whether they are better than food sources is disputed. Given that flavonoids encompass a class of 6000 compounds, it is not surprising that there is no generic statement to be made about the efficacy of flavonoid supplements.

“There isn’t enough research on flavonoid supplements, most of the research has been done in the context of food stuffs. Consuming these compounds within the context of foods (fruits and vegetables) is the safest and probably best way to do so,” Rendeiro says.

The authors of a 2011 review published in Advances in Nutrition which examined the effect of flavonoids in food versus in supplements, point out that flavonoids exist in a biochemical context inside of fruits and vegetables, which contain a mixture of secondary metabolites.

“This complex mixture of secondary plant metabolites cannot be simulated by single purified compounds as dietary supplements,” write the authors.

The Oregon State University Linus Pauling Institute Micronutrient Information Center warns that supplemental flavonoids may interact with certain prescription drugs. Such interactions have the potential to increase the toxicity of certain drugs or contribute to overdose.

As always, before you embark on any supplement regime, speak to your healthcare professional.