Proanthocyanidins—also called "OPCs" for oligomeric procyanidins or "PCOs" for procyanidolic oligomers—are a class of nutrients belonging to the flavonoid family.
Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.
For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.
3 StarsReliable and relatively consistent scientific data showing a substantial health benefit.
2 StarsContradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1 StarFor an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.
This supplement has been used in connection with the following health conditions:
Chronic Venous Insufficiency
50 to 100 mg two to three times daily
Proanthocyanidins, a group of flavonoids, have been shown to strengthen capillaries in double-blind research.
(OPCs), a group of flavonoids found in pine bark, grape seed, grape skin, bilberry, cranberry, black currant, green tea, black tea, and other plants, have also been shown to strengthen capillaries in double-blind research using as little as two 50 mg tablets per day. In a double-blind trial using a total of 150 mg OPCs per day, French researchers reported reduced symptoms for women with CVI. In another French double-blind trial, supplementation with 100 mg taken three times per day resulted in benefits within four weeks.
100–400 mg per day
Grape seed extract may lower blood pressure in people with pre-hypertension and mild hypertension, especially in those with other metabolic disturbances.
Grape seeds contain polyphenolic compounds called proanthocyanidins that have powerful antioxidant properties. Grape seed extract has been found in clinical trials to improve blood vessel elasticity and reduce high blood pressure in those with pre-hypertension and mild hypertension. A meta-analysis of 16 randomized controlled trials with a combined total of 810 participants found grape seed extract can reduce high blood pressure, and the effect was stronger in younger individuals and those with metabolic disturbances like obesity.
150 mg daily
Proanthocyanidins, flavonoids extracted from grape seeds, have been shown to increase capillary strength in people with hypertension and diabetes.
Compounds called flavonoids may help strengthen weakened capillaries. In test tube and animal studies, they have been shown to protect collagen, one of the most important components of capillary walls. A preliminary study found that (flavonoids extracted from grape seeds), 150 mg per day, increased capillary strength in people with hypertension and/or diabetes. A double-blind trial found a combination of two flavonoids (900 mg per day of diosmin and 100 mg per day hesperidin) for six weeks reduced symptoms of capillary fragility. Use of vitamin C with flavonoids, particularly quercetin, rutin, and hesperidin, is sometimes recommended for capillary fragility. Doctors often recommend 400 mg of rutin or quercetin three times per day or 1 gram of citrus flavonoids three times per day.
150 mg daily
Proanthocyanidins, a group of flavonoids found in pine bark, grape seed, and other plant sources, may help slow the progression of diabetic retinopathy.
(OPCs), a group of flavonoids found in pine bark, grape seed, and other plant sources have been reported in preliminary French trials to help limit the progression of retinopathy. In one controlled trial, 60% of people with diabetes taking 150 mg per day of OPCs from grape seed extract had no progression of retinopathy compared to 47% of those taking a placebo.
1.1 to 1.66 mg per 2.2 lbs (1 kg) of body weight per day during periods of high sun exposure
Proanthocyanidins are a group of flavonoids found in pine bark, grape seed, and other plant sources that may increase the amount of ultraviolet rays necessary to cause sunburn.
Trials have tested combinations of several antioxidants. One preliminary study found that a daily combination of beta-carotene (6 mg), lycopene (6 mg), vitamin E (15 IU), and selenium for seven weeks protected against ultraviolet light. However, a double-blind trial of a combination of smaller amounts of several carotenoids, vitamins C and E, selenium, and did not find significant UV protection compared with placebo. Similarly, in a controlled trial, a combination of selenium, copper, and vitamins was found to be ineffective.
(OPCs) are a group of flavonoids found in , , and other plant sources. In a preliminary trial, volunteers were supplemented with Pycnogenol, an extract of French maritime pine bark rich in OPCs, in the amount of 1.1 mg per 2.2 pounds of body weight per day for the first four weeks, and 1.66 mg per 2.2 pounds of body weight per day for the next four weeks. Compared with ultraviolet sensitivity before supplementation, the lower amount of Pycnogenol was found to significantly increase the amount of ultraviolet rays necessary to cause sunburn, and the higher amount was significantly more effective than the lower amount.
Refer to label instructions
In a preliminary report, three patients with chronic pancreatitis who were treated with grape seed extract saw reduced frequency and intensity of abdominal pain.
In a preliminary report, three patients with chronic pancreatitis were treated with in the amount of 100 mg 2–3 times per day. The frequency and intensity of abdominal pain was reduced in all three patients, and there was a resolution of vomiting in one patient.
Refer to label instructions
One trial found that supplementing with proanthocyanidins improved the function of leg veins in people with widespread varicose veins.
A small, preliminary trial found that supplementation with 150 mg of per day improved the function of leg veins after a single application in people with widespread varicose veins. Double-blind trials are needed to determine whether extended use of proanthocyanidins can substantially improve this condition.
How It Works
How to Use It
Where to Find It
Proanthocyanidins can be found in many plants, most notably pine bark, grape seed, and grape skin. However, bilberry, cranberry, black currant, green tea, black tea, and other plants also contain these flavonoids. Nutritional supplements containing proanthocyanidins extracts from various plant sources are available, alone or in combination with other nutrients, in herbal extracts, capsules, and tablets.
Flavonoids and proanthocyanidins are not classified as essential nutrients because their absence does not induce a deficiency state. However, proanthocyanidins may have many health benefits, and anyone not eating the various plants that contain them would not derive these benefits.
Interactions with Supplements, Foods, & Other Compounds
Interactions with Medicines
Flavonoids, in general, and proanthocyanidins, specifically, have not been associated with any consistent side effects. As they are water-soluble nutrients, excess intake is simply excreted in the urine.
Last Review: 03-24-2015
Copyright © 2023 TraceGains, Inc. All rights reserved.
The information presented by TraceGains is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires December 2023.