Proanthocyanidins (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.^1,2 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.³

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.⁴ However, a double-blind trial of a combination of smaller amounts of several carotenoids, vitamins C and E, selenium, and proanthocyanidins did not find significant UV protection compared with placebo.⁵ Similarly, in a controlled trial, a combination of selenium, copper, and vitamins was found to be ineffective.⁶

Proanthocyanidins (OPCs) are a group of flavonoids found in pine bark, grape seed, 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.⁷ 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.

Proanthocyanidins (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.^8,9 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.¹⁰

Proanthocyanidins (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.¹¹ In a double-blind trial using a total of 150 mg OPCs per day, French researchers reported reduced symptoms for women with CVI.¹² In another French double-blind trial, supplementation with 100 mg taken three times per day resulted in benefits within four weeks.¹³

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.^14,15 A preliminary study found that proanthocyanidins (flavonoids extracted from grape seeds), 150 mg per day, increased capillary strength in people with hypertension and/or diabetes.¹⁶ 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.¹⁷ Use of vitamin C with flavonoids, particularly quercetin, rutin, and hesperidin, is sometimes recommended for capillary fragility.¹⁸ Doctors often recommend 400 mg of rutin or quercetin three times per day or 1 gram of citrus flavonoids three times per day.

A small, preliminary trial found that supplementation with 150 mg of proanthocyanidins per day improved the function of leg veins after a single application in people with widespread varicose veins.¹⁹ Double-blind trials are needed to determine whether extended use of proanthocyanidins can substantially improve this condition.