Flavones represent a specific category of naturally occurring compounds found in various plants. These compounds are secondary metabolites, meaning they are not directly involved in the primary growth or development of the plant but play roles in its defense and other functions. Present in many fruits, vegetables, and herbs, flavones are a subject of increasing interest due to their biological activities in humans.
Flavones Within the Flavonoid Family
Flavones belong to a larger, diverse group of plant compounds known as flavonoids, which are characterized by a 15-carbon skeleton consisting of two phenyl rings and a heterocyclic oxygen-containing ring. Flavones are specifically defined by their chemical backbone, known as 2-phenylchromen-4-one, which includes a double bond between positions 2 and 3 of their central C-ring and a ketone group at position 4.
This structural feature distinguishes them from other flavonoid subclasses, such as flavonols, which possess an additional hydroxyl group at position 3 of the C-ring, or flavanones, where the double bond between positions 2 and 3 of the C-ring is saturated. Isoflavones, another distinct subclass, have their B-ring attached at position 3 of the C-ring, unlike flavones where it is at position 2.
Natural Sources of Flavones
Flavones are widely distributed across the plant kingdom and can be found in numerous dietary and herbal sources. Common vegetables rich in these compounds include celery, parsley, red peppers, spinach, and carrots. Herbs such as chamomile, mint, thyme, oregano, and sage also contain notable amounts of flavones.
Specific examples include apigenin O-glycosides found in chamomile flower and peppermint, while luteolin is present in Chinese celery and kiwi fruit. Dried parsley is recognized for its particularly high concentration of flavones, significantly exceeding levels found in many other herbs or vegetables.
Biological Activities of Flavones
Flavones are recognized for their broad biological activities within the body, largely attributed to their antioxidant and anti-inflammatory properties. As antioxidants, flavones help neutralize reactive oxygen species (ROS), often referred to as free radicals. Their mechanisms of action include directly scavenging these radicals, inhibiting enzymes involved in their formation, and chelating trace metals that catalyze radical generation.
Beyond their antioxidant role, flavones demonstrate anti-inflammatory effects by influencing several biochemical pathways. They can modulate immune cytokines and inhibit enzymes like cyclooxygenase (COX) and lipoxygenase, which are involved in inflammatory processes. Furthermore, flavones may affect the function of protein kinases, enzymes that play a part in generating inflammatory responses, by binding to their catalytic sites.
Notable Flavones and Their Functions
Among the numerous flavones, apigenin and luteolin are two of the most extensively studied, each with distinct sources and recognized functions.
Apigenin is abundant in chamomile, parsley, and celery, contributing to the calming effects often associated with chamomile tea. This flavone has also been explored for its potential role in supporting brain neurovascular health and influencing glucose metabolism.
Luteolin is another well-known flavone found in diverse sources such as celery, carrots, parsley, and various herbs like oregano and thyme. It has shown neuroprotective properties, with studies indicating its ability to cross the blood-brain barrier, protect brain cells from oxidative stress, and potentially enhance nerve development. It also functions as a natural antihistamine by preventing mast cell degranulation, which can alleviate allergic symptoms.
Consumption and Supplement Safety
The most recommended way to obtain flavones is through a balanced diet rich in fruits, vegetables, and herbs. The estimated daily intake of flavones from a typical diet is relatively low, often less than 2 mg per day.
Regarding supplements, there are currently no official Recommended Daily Allowances (RDAs) established for flavones. The supplement market for these compounds is largely unregulated, and isolated flavones may have poor bioavailability compared to those consumed naturally in foods. Individuals considering flavone supplements should consult a healthcare provider, especially if they are pregnant or breastfeeding, have existing health conditions, or are taking medications like blood thinners, as potential interactions or adverse effects have not been fully established.